Iron supplementation in pregnant Danish women revisited: Effects on prepartum and postpartum iron deficiency,anemia,serum erythropoietin;including iron status,erythropoietin and anthropometrics in newborns. A randomized,placebo-controlled study

Abstract

OBJECTIVE:

To assess effects of iron supplementation, 66 mg elemental iron daily as ferrous fumarate, on iron status markers during normal pregnancies.

METHODS:

Randomized, double-blind, placebo-controlled study of 119 women (62 iron-, 57 placebo -treated) and their newborns. Hemoglobin (Hb), serum (S)-ferritin, S-transferrin saturation percentage (TSAT) and S-erythropoietin (S-EPO) were measured at 14–18, 24–27 weeks of gestation, prepartum, 1 and 8 weeks postpartum.

RESULT:

From 24–27 weeks gestation to 8 weeks postpartum, the iron group had higher Hb, S-ferritin and TSAT than the placebo group; prepartum, 11% had iron deficiency (ID) and 0% iron deficiency anemia (IDA) in the iron group, vs 60% and 18% in the placebo group; 8 weeks postpartum 1.6% in the iron group had ID and 1.6% IDA vs 14% and 7% in the placebo group. S-EPO levels in the iron group were lower than in the placebo group (p < 0.001). Mothers prepartum S-EPO values were correlated to newborns cord S-EPO values (p < 0.001). Newborns to iron treated mothers had higher cord S-ferritin levels than those to placebo treated mothers (p = 0.02). Newborn girls had higher cord S-ferritin levels than boys (p < 0.01). There was no impact of iron supplementation on the length of gestation, placental weight, or newborns birth weight. Birth weight was correlated only with mothers’ body weight, length of gestation and placental weight.

CONCLUSION:

Iron supplementation had a “positive” impact on iron status and Hb both during pregnancy and postpartum, with a low frequency of ID/IDA and also a “positive” influence on newborns iron status.

Keywords

Anemia iron deficiency birth weight erythropoietin fetal blood infant newborn iron supplement placebo-controlled study pregnancy

1 Introduction

During pregnancy, the physiologic needs for iron become extraordinarily high. The average requirements for absorbed iron increase gradually from 0.8 mg/day in the early first trimester to 7.5 mg/day in the third trimester, and the average requirement in the entire gestation period is approximately 4.4 mg/day [1 –3].

In Europe, including Denmark, a high percentage of women of reproductive age have a low body iron status with median serum ferritin levels ranging from 26–38μg/L, corresponding to mobilizable body iron reserves of 200–300 mg, and 45–55% have small or depleted iron stores (serum ferritin ≤30μg/L). Only about 20–35% have ferritin levels above 70μg/L, corresponding to mobilizable iron reserves of 500 mg or more, which appears to be sufficient to complete a pregnancy without iron supplementation and without developing iron deficiency (ID) or iron deficiency anemia (IDA) [4, 5]. However, in comparison with the high demands for iron in pregnancy, dietary iron intake in pregnant women in Europe, including Denmark is insufficient and markedly below the official national dietary recommendations [6]. Consequently, iron supplementation during pregnancy should be considered in women having serum ferritin levels below 70μg/L preconceptional or in early pregnancy [7].

The purpose of this paper, comprising healthy ethnic Danish women, is threefold: firstly to evaluate the frequency of prepartum and postpartum anemia, ID and IDA before and after normal pregnancy and delivery with and without iron supplementation; secondly to assess the correlation between iron status markers at different time points in pregnancy and postpartum, and thirdly to examine the influence of iron supplementation and the mothers iron status on the length of gestation, and the anthropometric development and iron status of the newborns.

2 Subjects and methods

The study was approved by the Regional Ethics Committee and oral as well as written informed consent was obtained from all participants. The study fulfilled the Declaration of Helsinki. The investigation was designed as a double-blind, placebo-controlled, block-randomized study of which the details have been published in a previous paper [8]. However, compared to the first publication [8] the data have been analyzed from a different aspect and in more details concerning 1) the impact of iron supplementation on iron status one and 8 weeks postpartum, 2) analysis of factors influencing gestational length, including placental weight and mothers iron status, 3) analysis of iron status in newborns and association with newborns’ gender, anthropometrics, and mothers iron status, 4) analysis of anthropometrics and gender in newborns and association with gestational length and iron status in newborns and mothers, 5) analysis of serum erythropoietin (S-EPO) and the association with iron status in newborns. These results have not previously been published.

2.1 Women

This study, which was performed from January 1st 1985 until August 25th 1986, included 119 healthy ethnic Danish women from both urban but mainly rural areas, who in 1985 consecutively attended the Birth Clinic at Herning Hospital in Jutland, Denmark, within 14–18 weeks of gestation [8]. All women had their iron status markers (hemoglobin (Hb), serum (S–) ferritin and S-transferrin saturation% (TSAT) as well as S-EPO monitored on a regular basis [8]. From the original series of 120 women [8], one woman was excluded due to severe obesity and polycythemia/polyglobulia. Women smoking more than 9 cigarettes/day were not included. Gestational age was determined by ultrasound. The final criteria for inclusion were: healthy pregnant women with a normal single pregnancy and a normal delivery with an estimated blood loss of less than 500 mL [8].

The women were randomly allocated into two groups; 62 women to take one tablet containing ferrous fumarate 200 mg (66 mg elemental iron) daily and 57 women to take a similarly looking tablet containing placebo daily. The women were not given instruction concerning the temporal intake of the tablets, so it is not known whether they took the tablets with a meal or between meals. After inclusion, the women were followed-up with blood samples at regular intervals during the remaining period of gestation, prepartum as well as one week and 8 weeks postpartum. Placental weight was recorded after delivery.

2.2 Newborns

Cord blood was obtained immediately after birth and serum immediately frozen at –25°C. Apgar scores and anthropometric measures were recorded.

2.3 Statistics

The original data from the initial study [8] were entered into the statistical program MedCalc® [9]. Data were checked for normality using the D’Agostino-Pearson test. In normally distributed variables, arithmetic mean±SD (standard deviation) is quoted, and Student’s t-tests for paired and unpaired values and Pearson’s correlation coefficient r were used. In non-normally distributed variables, median and 2.5–97.5 percentiles are quoted, and Mann-Whitney’s U test and Spearman’s rank correlation coefficient rho (r_s) were employed. Qualitative data were evaluated by Fisher’s exact test. Logarithmic (log₁₀) transformation was performed in the non-normally distributed variables S-ferritin and S-erythropoietin (EPO), which became normally distributed after this procedure. After calculation of the arithmetic mean and SD of log₁₀ values, the geometric mean and geometric SD were calculated as antilog₁₀ values of arithmetic mean and SD. A p-value of ≤0.05 was considered statistically significant. In the following text and tables, log₁₀ values are denoted “log” values.

2.4 Iron status markers

Blood samples were obtained by venipuncture in the non-fasting state. Hb was analyzed immediately on Coulter-S®; the intra-assay coefficient of variation was 0.5–0.6% [10]. Conversion between Hb units is: Hb in g/L×0.0621 = Hb in mmol/L. Serum samples were frozen immediately at –25°C and all samples were subsequently analysed together after closure of the study. S-ferritin was measured by a radioimmunoassay (Ferritin RIA Amersham®) [11]. The intra-assay coefficient of variation was 6.8% at a S-ferritin concentration of 13μg/L and 4.5% at concentrations > 30μg/L [11]. The assay was calibrated according to the WHO Human Liver Ferritin International Standard 80/602 [11]. S-EPO was measured by an in-house radioimmunoassay [12]. S-iron, S-transferrin and TSAT were analyzed by previously described methods [13].

2.5 Definition of iron status

S-ferritin values < 15μg/L are considered to indicate depleted or absent body iron reserves and indicative of ID [14, 15]. Ferritin values ≥30μg/L are indicative of body iron reserves with stainable hemosiderin in the bone marrow and values < 30μg/L indicate small or depleted iron reserves [14]. Hb values < 110 g/L (6.8 mmol/L) are considered consistent with anemia during pregnancy [16 –18]. The combination of Hb < 110 g/L and ferritin < 15μg/L are considered consistent IDA. At 8 weeks postpartum the discriminatory Hb value for anemia is < 120 g/L (7.4 mmol/L) [17, 18]. A TSAT < 15% is considered indicative of insufficient supply of iron to the tissues, including the erythropoietic tissue [19].

3 Results

3.1 Pregnant women

The two groups were comparable concerning gestational age at inclusion, body height, body weight, body mass index (BMI) and parity (Table 1). The number of tablets consumed per woman was higher in the iron group, mean 159±38 (SD) vs 93±43 in the placebo group (p < 0.001).

Table 1
Data on the 119 women included in the iron supplementation study. Gestational age at inclusion, age at inclusion, body mass index, parity, total length of gestation and placental weight. Values are arithmetic mean±standard deviation for normally distributed variables, median and observed range for non-normally distributed variables

Gestational age at inclusion days Age yrs BMI kg/m² Parity n Length of gestation days Placental weight g

Iron n = 62 114±20 26±4.5 20.9 2 281 633±127

14.6–31.2 1–3 256–297

Placebo n = 57 117±19 27±4.0 20.6 2 282 658±128

17.2–29.4 1–4 258–299

P-value ns ns ns ns ns ns

	Gestational age at inclusion days	Age yrs	BMI kg/m²	Parity n	Length of gestation days	Placental weight g
Iron n = 62	114±20	26±4.5	20.9	2	281	633±127
			14.6–31.2	1–3	256–297
Placebo n = 57	117±19	27±4.0	20.6	2	282	658±128
			17.2–29.4	1–4	258–299
P-value	ns	ns	ns	ns	ns	ns

BMI = body mass index; ns = not significant. ^*Student’s t-test for unpaired values in normally distributed variables; Mann-Whitney test in non-normally distributed variables.

3.1.1 Length of gestation, iron status and placental weight

In the entire series of 119 women, gestational age at delivery was median 282 days (range 256–299 days). Length of gestation and placental weight were not significantly different in iron and placebo treated women (Table 1). There were no correlations between the length of gestation and the iron status markers, Hb, S-ferritin, TSAT or S-EPO at any time point during gestation. Likewise, there were no correlations between placental weight and length of gestation, Hb, S-ferritin, TSAT and S-EPO at any time point during gestation.

3.1.2 Hemoglobin

There was no significant difference between the mean Hb concentrations in iron and placebo treated women at inclusion (Table 2); however, a significantly higher number of women in the placebo group vs the iron group had Hb values < 110 g/L (Table 3). In the iron group, Hb values declined to a nadir during gestational weeks 24–27 and subsequently increased until delivery (Table 2). Hb values prepartum and one week postpartum were similar and followed by a subsequent significant increase at 8 weeks postpartum. In the placebo group, a similar pattern of variation was observed; however, at every time point after inclusion, Hb values were significantly higher in the iron group compared to the placebo group, also including one week and 8 weeks postpartum.

Table 2
Blood hemoglobin concentrations in women at different time points during pregnancy, prepartum, 1 week and 8 weeks postpartum, according to iron supplementation. Values are arithmetic mean±standard deviation

Gestation Weeks 14–18 Weeks 24–27 PreP 1 week PostP 8 weeks PostP

Iron n = 62

Hemoglobin, g/L 122±8.8 117±7.5 128±8.8 128±13.4 134±7.2

P-value^* < 0.0001 < 0.0001 ns 0.0004

Placebo n = 57

Hemoglobin, g/L 119±8.8 114±7.5 116±9.8 118±11.7 128±9.1

P-value^* < 0.0001 0.06 ns < 0.0001

Iron vs placebo

P-value^** ns 0.03 < 0.0001 < 0.0001 0.0001

Gestation	Weeks 14–18		Weeks 24–27	PreP	1 week PostP	8 weeks PostP
Iron n = 62
Hemoglobin, g/L	122±8.8		117±7.5	128±8.8	128±13.4	134±7.2
P-value^*		< 0.0001		< 0.0001	ns	0.0004
Placebo n = 57
Hemoglobin, g/L	119±8.8		114±7.5	116±9.8	118±11.7	128±9.1
P-value^*		< 0.0001		0.06	ns	< 0.0001
Iron vs placebo
P-value^**	ns		0.03	< 0.0001	< 0.0001	0.0001

PreP = prepartum; PostP = postpartum. ^*Student’s t-test for paired values; ^**Student’s t-test for unpaired values; ns = not significant.

Table 3

Number of women with hemoglobin concentrations below the World Health Organization’s recommended cut-off levels for anemia at different gestational ages [16], prepartum and postpartum according to iron supplementation

Gestation	Weeks 14–18	Weeks 24–27	PreP	1 week PostP		8 weeks PostP
Hemoglobin, g/L	< 110	< 110	< 110	< 100	< 110	< 120
Iron n = 62	1/62 –1.6%	10/62 –16.1%	0/62 –0%	1/62 –1.6%	9/62 –14.5%	2/62 –3.2%
Placebo n = 57	9/57 –15.8%	16/57 –28.1%	14/57 –24.6	3/57 –5.3%	12/57 –21.1%	9/57 –15.8%
Iron vs placebo
P-value^*	0.007	ns	< 0.0001	ns	ns	0.03

PreP = prepartum; PostP = postpartum; ns = not significant. ^*Fisher’s exact test.

The observed changes in Hb concentrations exceeding±4% [10], from prepartum to one week postpartum were not significantly different in the iron and placebo group. In the iron group, Hb levels increased in 45%, were unchanged in 27.5% and decreased in 27.5% of the women; in the placebo group, the corresponding figures were 35.1%, 24.6% and 24.6% of the women, respectively, (p =0.7).

The frequency of anemia prepartum and 8 weeks postpartum was significantly lower in the iron group than in the placebo group (Table 3). Prepartum, none of the women in the iron group vs 25% in the placebo group were anemic. Eight weeks postpartum, 3% of women in the iron group were anemic vs 16% in the placebo group. In iron treated women, the Hb 2.5 percentile was 110 g/L (6.8 mmol/L) prepartum, and 100 g/L (6.2 mmol/L) one week postpartum, while the corresponding figures in placebo treated women were 97 g/L (6.0 mmol/L) and 94 g/L (5.9 mmol/L), respectively.

There were significant correlations between Hb levels at inclusion and levels at gestational weeks 24–27, prepartum, one week and 8 weeks postpartum, as well as between Hb levels prepartum and postpartum (Table 4). The correlations were overall slightly higher in the placebo group compared to the iron group.

Table 4

Correlations between womens hemoglobin concentrations at different time points during gestation, prepartum, one week and 8 weeks postpartum, according to iron supplementation

Women n =	All 119		Iron 62		Placebo 57
Hemoglobin	r	P	r	P	r	P
Weeks 14–18 vs weeks 24–27	0.69	< 0.0001	0.64	< 0.0001	0.72	< 0.0001
Weeks 14–18 vs PreP	0.45	< 0.0001	0.55	< 0.0001	0.33	0.01
Weeks 14–18 vs PostP 1 week	0.29	0.002	0.13	0.3	0.38	0.004
Weeks 14–18 vs PostP 8 weeks	0.43	< 0.0001	0.32	0.012	0.46	0.0003
PreP vs PostP 1 week	0.47	< 0.0001	0.20	0.13	0.51	0.0001
PreP vs PostP 8 weeks	0.42	< 0.0001	0.13	0.3	0.43	0.0009
PostP 1 week vs PostP 8 weeks	0.51	< 0.0001	0.35	0.006	0.54	0.0001

PreP = prepartum; PostP = postpartum; r = Pearson’s correlation coefficient.

3.1.3 Serum ferritin

There was no significant difference between the mean log S-ferritin concentrations in iron and placebo treated women at inclusion (Tables 5 6), and there was no correlation between S-ferritin at inclusion and BMI. At inclusion, 27.7% of the women had S-ferritin values < 30μg/L indicating small or absent hemosiderin iron reserves in the bone marrow [13], and 4.2% had S-ferritin < 15μg/L indicating ID [12]. In both the iron and placebo group, S-ferritin declined significantly from inclusion reaching a nadir prepartum and subsequently increased to a level at one week postpartum, which remained stable until 8 weeks postpartum (Table 5). At every time point after inclusion S-ferritin values were significantly higher in the iron group compared to the placebo group, including one week and 8 weeks post-partum.

Table 5
Serum ferritin concentrations in women at different time points during pregnancy, prior to delivery, 1 week and 8 weeks postpartum. Values are arithmetic mean±SD of log values, and geometric mean±geometric SD (antilog of arithmetic mean±SD)

Serum ferritin, μg/L

Gestation Weeks 14–18 Weeks 24–27 PreP 1 week PostP 8 weeks PostP

Iron n = 62

Arithmetic mean±SD 1.6613±0.3038 1.4416±0.2610 1.3644±0.2089 1.6290±0.2090 1.6626±0.3162

Geometric mean±SD 46±2.0 28±1.8 23±1.6 43±1.6 46±2.1

P-value^* < 0.0001 0.0026 < 0.0001 ns

Placebo n = 57

Arithmetic mean±SD 1.6326±0.3011 1.3043±0.2838 1.1291±0.1553 1.3745±0.2029 1.3600±0.1746

Geometric mean±SD 43±2.0 20±1.9 13±1.4 24±1.6 23±1.5

P-value^* < 0.0001 < 0.0001 < 0.0001 ns

Iron vs placebo

P-value^** ns 0.007 < 0.0001 < 0.0001 < 0.0001

	Serum ferritin, μg/L
Iron n = 62
Arithmetic mean±SD	1.6613±0.3038	1.4416±0.2610	1.3644±0.2089	1.6290±0.2090	1.6626±0.3162
Geometric mean±SD	46±2.0	28±1.8	23±1.6	43±1.6	46±2.1
P-value^*		< 0.0001	0.0026	< 0.0001	ns
Placebo n = 57
Arithmetic mean±SD	1.6326±0.3011	1.3043±0.2838	1.1291±0.1553	1.3745±0.2029	1.3600±0.1746
Geometric mean±SD	43±2.0	20±1.9	13±1.4	24±1.6	23±1.5
P-value^*		< 0.0001	< 0.0001	< 0.0001	ns
Iron vs placebo
P-value^**	ns	0.007	< 0.0001	< 0.0001	< 0.0001

PreP = prepartum; PostP = postpartum; SD = standard deviation; ns = not significant. Iron group: weeks 14–18 vs one week and 8 weeks PostP: ns. Placebo group: weeks 14–18 vs one week and 8 weeks PostP: p < 0.0001. ^*Student’s t-test paired values ^**Student’s t-test unpaired values.

Table 6

Number of women with serum ferritin concentrations below defined cut-off levels [12, 13] at different gestational ages, prepartum and postpartum, according to iron supplementation

Gestation	Weeks 14–18		Weeks 24–27	PreP	1 week PostP	8 weeks PostP
Ferritin, μg/L	< 15	< 30	< 15	< 15	< 15	< 15	< 30
Iron n = 62	2/62 –3.2%	18/62 –29.0%	4/62 –6.5%	7/62 –11.3%	0/62 –0%	1/62 –1.6%	23/62 –37.1%
Placebo n = 57	3/57 –5.3%	15/57 –26.3%	18/57 –31.6%	34/57 –59.7%	9/57 –15.8%	8/57 –14.0%	43/57 –75.4%
Iron vs placebo
P-value^*	ns	ns	0.0007	< 0.0001	< 0.001	0.013	< 0.0001

Iron group: weeks 14–18 vs one week and 8 weeks PostP: Ferritin < 15μg/L, p = 0.9 and ferritin < 30μg/L, p = 0.2. Placebo group: Weeks 14–18 vs one week and 8 weeks PostP: Ferritin < 15μg/L, p = 0.2 and ferritin < 30μg/L, p < 0.0001. PreP = prepartum; PostP = postpartum. ^*Fisher’s exact test ns = not significant.

The frequency of ID is shown in Table 6. Prepartum, in the iron group, 11.3% vs 59.7% in the placebo group had ID. One week postpartum, none in the iron group vs 15.8% in the placebo group had ID and these figures remained stable until 8 weeks postpartum. At every time point after inclusion the frequency of ID and of S-ferritin values < 30μg/L were significantly higher in the placebo group compared to the iron group, including one week and 8 weeks postpartum.

In the iron group, S-ferritin levels at inclusion were not significantly different from levels at one week and 8 weeks postpartum, whereas in the placebo group, ferritin levels at one week and 8 weeks postpartum were significantly lower than levels at inclusion.

In the entire series, as well as in the iron and placebo group, there were significant correlations between log S-ferritin levels at inclusion and subsequent log S-ferritin levels at gestational weeks 24–27, prepartum, one week and 8 weeks postpartum (Table 7). Likewise, log S-ferritin levels prepartum showed correlations with log ferritin levels one week and 8 weeks postpartum.

Table 7

Correlations between womens log₁₀ serum ferrritin concentrations at different time points during gestation, prepartum, one week and 8 weeks postpartum according to iron supplementation

Women n =	All 119		Iron 62		Placebo 57
Log₁₀ ferritin	r	P	r	P	r	P
Weeks 14–18 vs weeks 24–27	0.78	< 0.0001	0.78	< 0.0001	0.82	< 0.0001
Weeks 14–18 vs PreP	0.34	0.0001	0.48	0.0001	0.23	0.08
Weeks 14–18 vs PostP 1 week	0.39	< 0.0001	0.40	0.001	0.45	0.0004
Weeks 14–18 vs PostP 8 weeks	0.20	0.03	0.16	0.2	0.34	0.01
PreP vs PostP 1 week	0.64	< 0.0001	0.64	< 0.0001	0.30	0.2
PreP vs PostP 8 weeks	0.54	< 0.0001	0.45	0.0002	0.15	0.3
PostP 1 week vs PostP 8 weeks	0.63	< 0.0001	0.63	< 0.0001	0.28	0.04

PreP = prepartum; PostP = postpartum; r = Pearson’s correlation coefficient.

In the separate iron and placebo groups there were no consistent correlations between log S-ferritin and Hb levels during pregnancy. However, in the entire series there were significant positive correlations between log S-ferritin and Hb values prepartum (r = 0.41, p < 0.0001), one week postpartum (r = 0.42, p < 0.0001) and 8 weeks postpartum (r = 0.34, p = 0.0002) but not at other time points.

3.1.4 S-transferrin saturation

There was no significant difference between TSAT levels in iron and placebo treated women at inclusion (Tables 8 9). At every time point after inclusion TSAT values were significantly higher in the iron group compared to the placebo group, including one week and 8 weeks postpartum. At inclusion, none of the women had TSAT values < 15% indicating insufficient iron supply to the tissues. In both the iron and placebo group, TSAT declined significantly from inclusion reaching a nadir one week postpartum and subsequently increased to a higher stable level at 8 weeks postpartum (Table 8). In the iron group, TSAT at 8 weeks postpartum were similar to levels at inclusion (p = 0.6), while in the placebo group, levels at 8 weeks postpartum were significantly lower than levels at inclusion (p = 0.003). The frequency of TSAT levels < 15% was significantly lower in the iron group both prepartum (6.5%) and one week postpartum (21%) than in the placebo group (54.4% and 64.9%, respectively).

Table 8
Serum transferrin saturation in women at different time points during pregnancy, prior to delivery, 1 week and 8 weeks postpartum, according to iron supplementation. Values are arithmetic mean±standard deviation

Serum transferrin saturation%

Gestation Weeks 14–18 Weeks 24–27 PreP 1 week PostP 8 weeks PostP

Iron n = 62

TSAT% 36±10 30±8 28±10 20±7 35±14

P-value < 0.0001 < 0.0001 < 0.0001 < 0.0001

Inclusion vs 8 weeks PostP: ns

Placebo n = 57

TSAT% 33±10 22±8 15±6 15±6 29±10

P-value < 0.0001 < 0.0001 ns < 0.0001

Inclusion vs 8 weeks PostP: p = 0.003

Iron vs placebo

P-value^* ns < 0.0001 < 0.0001 < 0.0001 0.009

Serum transferrin saturation%
Iron n = 62
TSAT%	36±10		30±8		28±10		20±7		35±14
P-value		< 0.0001		< 0.0001		< 0.0001		< 0.0001
Inclusion vs 8 weeks PostP: ns
Placebo n = 57
TSAT%	33±10		22±8		15±6		15±6		29±10
P-value		< 0.0001		< 0.0001		ns		< 0.0001
Inclusion vs 8 weeks PostP: p = 0.003
Iron vs placebo
P-value^*	ns		< 0.0001		< 0.0001		< 0.0001		0.009

PreP = prepartum; PostP = postpartum; TSAT% = serum transferrin saturation%; ns = not significant; ^*Fisher’s exact test.

Table 9

Number of women with serum transferrin saturation below the standard cut-off level at different time points during pregnancy, prior to delivery, 1 week and 8 weeks postpartum, according to iron supplementation

Serum transferrin saturation %
Gestation	Weeks 14–18	Weeks 24–27	PreP	1 week PostP	8 weeks PostP
Iron n = 62
TSAT < 15%	0/62 –0%	0/62 –0%	4/62 –6.5%	13/62 –21.0%	3/62 –4.8%
Placebo n = 57
TSAT < 15%	0/57 –0%	11/57 –19.3%	31/57 –54.4%	37/57 –64.9%	5/57 –8.8%
Iron vs placebo
P-value^*	ns	< 0.001	< 0.0001	< 0.0001	ns

PreP = prepartum; PostP = postpartum; TSAT% = serum transferrin saturation%; ns = not significant; ^*Fisher’s exact test.

3.1.5 Iron deficiency anemia

The frequency of IDA is shown in Table 10. At gestational weeks 24–27 and prepartum, the iron treated women had significantly lower frequencies of IDA than the placebo treated women.

Table 10
Number of women with iron deficiency anemia (hemoglobin < 110 g/L and serum ferritin < 15μg/L) at different time points of gestation, prepartum and postpartum, according to iron supplementation

Hemoglobin < 110 g/L and Ferritin < 15μg/L

Gestation Weeks 14–18 Weeks 24–27 PreP 1 week PostP 8 weeks PostP^*

Iron n = 62 1/62 –1.6% 0/62 –0% 0/62 –0% 0/62 –0% 1/62 –1.6%

Placebo n = 57 0/57 –0% 5/57 –8.8% 10/57 –17.5% 3/57 –5.3% 4/57 –7.0%

Iron vs placebo

P-value^** ns 0.023 0.0004 ns ns

Hemoglobin < 110 g/L and Ferritin < 15μg/L
Iron n = 62	1/62 –1.6%	0/62 –0%	0/62 –0%	0/62 –0%	1/62 –1.6%
Placebo n = 57	0/57 –0%	5/57 –8.8%	10/57 –17.5%	3/57 –5.3%	4/57 –7.0%
Iron vs placebo
P-value^**	ns	0.023	0.0004	ns	ns

PreP = prepartum; PostP = postpartum; ns = not significant ^*Hemoglobin < 120 g/L ^**Fisher’s exact test.

3.1.6 Serum erythropoietin

S-EPO values, which became normally distributed after logarithmic transformation, are shown in Table 11. At inclusion, S-EPO levels were not significantly different in the iron and placebo treated groups. In both the iron treated and the placebo treated group, S-EPO increased significantly during gestation reaching a peak prepartum, and subsequently declining moderately one week postpartum, followed by a further, significant decline to 8 weeks postpartum. Prepartum, iron treated women had significantly lower S-EPO levels than placebo treated women, while the levels one week postpartum were slightly, although not significantly lower (Table 9); 8 weeks postpartum levels were almost similar in the two groups.

Table 11
Serum erythropoietin concentrations in women at different time points of gestation, prepartum and postpartum, according to iron supplementation. Values are arithmetic mean±standard deviation (SD) of log₁₀ values, and geometric mean and geometric SD (antilog₁₀ of log₁₀ arithmetic mean and SD)

Serum erythropoietin, U/L

Gestation Weeks 14–18 Weeks 24–27 PreP 1 week PostP 8 weeks PostP

Iron n = 59 60 56 51 44

Arithmetic mean±SD 1.3813±0.1463 1.4420±0.1143 1.4709±0.1324 1.4387±0.1795 1.2990±0.1378

Geometric mean±SD 24±1.4 28±1.3 30±1.4 28±1.5 20±1.4

P-value^* < 0.0001 ns ns < 0.0001

Placebo n = 55 57 51 47 44

Arithmetic mean±SD 1.3565±0.1460 1.4708±0.1667 1.5938±0.2369 1.4911±0.2017 1.3030±0.1259

Geometric mean±SD 23±1.4 30±1.5 39±1.7 31±1.6 20±1.3

P-value^* 0.0002 < 0.0001 0.028 < 0.0001

Iron vs placebo

P-value^** ns ns 0.0006 ns ns

	Serum erythropoietin, U/L
Iron n =	59		60		56		51		44
Arithmetic mean±SD	1.3813±0.1463		1.4420±0.1143		1.4709±0.1324		1.4387±0.1795		1.2990±0.1378
Geometric mean±SD	24±1.4		28±1.3		30±1.4		28±1.5		20±1.4
P-value^*			< 0.0001		ns		ns		< 0.0001
Placebo n =	55		57		51		47		44
Arithmetic mean±SD	1.3565±0.1460		1.4708±0.1667		1.5938±0.2369		1.4911±0.2017		1.3030±0.1259
Geometric mean±SD	23±1.4		30±1.5		39±1.7		31±1.6		20±1.3
P-value^*		0.0002		< 0.0001		0.028		< 0.0001
Iron vs placebo
P-value^**	ns		ns		0.0006		ns		ns

Weeks 14–18 vs 8 weeks PostP: Iron group, p = 0.005; Placebo group, p = 0.090. PreP = prepartum; PostP = postpartum; SD = standard deviation; ns = not significant. ^*Student’s t-test paired values ^**Student’s t-test unpaired values.

In the entire series, log S-EPO values showed significant negative correlations with Hb values both prepartum (r = –0.48, p < 0.0001) as well as one week postpartum (r = –0.52, p < 0.0001). However, in the iron treated group, the correlation prepartum was not significant (r = –0.10, p = 0.5) in contrast to the placebo treated group (r = –0.56, p < 0.0001). The correlations one week postpartum were significant both in the iron treated group (r = –0.68, p < 0.0001), and in the placebo treated group (r = –0.36, p = 0.013).

Likewise, in the entire series, prepartum log S-EPO values showed a significant inverse correlation with log S-ferritin values (r = –0.27, p = 0.005); however, the correlation was significant only in the placebo treated group (r = –0.31, p = 0.03), not in the iron treated group (r = –0.08, p = 0.5).

3.2 Newborns

3.2.1 Apgar score

Apgar scores in newborns 1, 3, 5, and 10 minutes after birth were median 10 (range 4–10) in the entire series, not being significantly different in the iron and placebo group. Apgar score at 3 minutes in the iron group was median 10 (range 7–10) and in the placebo group median 10 (range 6–10).

3.2.2 Birth weight

There were no significant differences between the newborns’ height, weight, BMI, weight/length ratio and boy/girl gender ratio in the iron and placebo group (Table 12). Boys had higher birth weight than girls, both in the entire group (mean 4.3% higher), in the iron group (mean 4.6% higher) and the placebo group (mean 4.0% higher), but the differences were not significant (Table 13). The were no significant differences between the length of gestation in boys and girls, neither in the entire group nor in the iron and placebo treated groups (data not shown).

Table 12
Anthropometric data in the 119 newborns in the iron supplementation study. Values are arithmetic mean±standard deviation

Newborns Weight g Length cm BMI kg/m² Weight/Length ratio kg/m Boy/Girl

Iron n = 62 3483±500 52±2.3 12.9±1.0 6.7±0.7 34/28

Placebo n = 57 3493±452 52±1.9 13.1±1.1 6.8±0.7 34/23

P-value^* ns ns ns ns ns^**

Newborns	Weight g	Length cm	BMI kg/m²	Weight/Length ratio kg/m	Boy/Girl
Iron n = 62	3483±500	52±2.3	12.9±1.0	6.7±0.7	34/28
Placebo n = 57	3493±452	52±1.9	13.1±1.1	6.8±0.7	34/23
P-value^*	ns	ns	ns	ns	ns^**

BMI = body mass index; ^*Student’s t-test unpaired values; ^**Fisher’s exact test; ns = not significant.

Table 13

Birth weight in newborn boys and girls according to iron supplementation. Values are arithmetic mean±standard deviation

		Weight boys g	Weight girls g
n =	68		51
	3551±468		3404±453
P-value		0.09
n =	34		28
Iron	3554±499		3397±497
P-value		ns
n =	34		23
Placebo	3548±490		3412±404
P-value		ns
P-value^*	ns		ns

Student’s t-test unpaired values; ^*Difference between iron and placebo group; ns = not significant.

Correlation analyses showed that birth weight in the entire group of children was significantly correlated with the length of gestation (r_s = 0.43, p < 0.0001), placental weight (r = 0.66, p < 0.0001), mother’s weight and mother’s BMI (r_s = 0.33, p = 0.0003) but not with mothers’ height (r_s = 0.07, p = 0.5). There were no correlations between birth weight, mothers’ Hb, log S-ferritin or log S-EPO at any time point during gestation.

3.2.3 Cord serum ferritin

Umbilical cord log S-ferritin values were normally distributed (Table 14). Cord S-ferritin levels were generally high, being significantly higher than the mothers prepartum S-ferritin levels both in the total series as well as in the iron and placebo groups (Students t-test for unpaired values p < 0.0001 in all groups). Only three newborns had S-ferritin values below 50μg/L.

Table 14
Log₁₀ cord serum ferritin and log₁₀ cord serum erythropoietin in newborns according to iron supplementation Values are arithmetic mean±standard deviation (SD) of log₁₀ values, and geometric mean and geometric SD (antilog₁₀ of log₁₀ arithmetic mean and SD)

Newborns S-ferritin boys + girls μg/L S-ferritin boys μg/L S-ferritin girls μg/L S-EPO boys + girls U/L S-EPO boys U/L S-EPO girls U/L

All n = 119 68 51 91 54 37

Arithmetic mean±SD 2.1602±0.2430 2.1072±0.2527 2.2314±0.2117 1.5474±0.2884 1.5812±0.3209 1.4979±0.2281

Geometric mean±SD 145±1.8 128±1.8 170±1.6 35±1.9 38±2.1 31±1.7

P-value 0.006 ns

Iron n = 62 34 28 47 26 21

Arithmetic mean±SD 2.2102±0.2008 2.1851±0.2134 2.2418±0.1827 1.5066±0.2639 1.4881±0.2863 1.5295±0.2381

Geometric mean±SD 162±1.6 153±1.6 175±1.5 32±1.8 31±1.9 34±1.7

P-value ns ns

Placebo n = 57 34 23 44 28 16

Arithmetic mean±SD 2.1059±0.2735 2.0269±0.2676 2.2192±0.2451 1.5909±0.3095 1.6677±0.3319 1.4566±0.2148

Geometric mean±SD 128±1.9 106±1.9 166±1.8 39±2.0 47±2.1 29±1.6

P-value 0.008 0.028

P-value^* 0.02 0.009 ns ns 0.039 ns

Newborns	S-ferritin boys + girls μg/L	S-ferritin boys μg/L		S-ferritin girls μg/L	S-EPO boys + girls U/L	S-EPO boys U/L		S-EPO girls U/L
All n =	119	68		51	91	54		37
Arithmetic mean±SD	2.1602±0.2430	2.1072±0.2527		2.2314±0.2117	1.5474±0.2884	1.5812±0.3209		1.4979±0.2281
Geometric mean±SD	145±1.8	128±1.8		170±1.6	35±1.9	38±2.1		31±1.7
P-value				0.006				ns
Iron n =	62	34		28	47	26		21
Arithmetic mean±SD	2.2102±0.2008	2.1851±0.2134		2.2418±0.1827	1.5066±0.2639	1.4881±0.2863		1.5295±0.2381
Geometric mean±SD	162±1.6	153±1.6		175±1.5	32±1.8	31±1.9		34±1.7
P-value					ns				ns
Placebo n =	57	34		23	44	28		16
Arithmetic mean±SD	2.1059±0.2735	2.0269±0.2676		2.2192±0.2451	1.5909±0.3095	1.6677±0.3319		1.4566±0.2148
Geometric mean±SD	128±1.9	106±1.9		166±1.8	39±2.0	47±2.1		29±1.6
P-value			0.008				0.028
P-value^*	0.02	0.009		ns	ns	0.039		ns

S-EPO = serum erythropoietin; SD = standard deviation; Student’s t-test unpaired values. ^*Difference between iron and placebo group; ns = not significant.

In the entire series, newborns to iron treated mothers had significantly higher ferritin values than newborns to placebo treated mothers (Table 14). Girls had consistently higher ferritin than boys, both in the entire series as well as in the iron and placebo treated groups (Table 14). Boys to iron treated mothers had significantly higher ferritin levels than boys to placebo treated mothers. Although ferritin levels in girls to iron treated mothers were higher than in girls to placebo treated mothers, the difference was not statistically significant (Table 14).

Correlation analyses showed no correlations between newborns log cord S-ferritin levels and mothers Hb, log S-ferritin or log S-EPO levels at any time point during gestation; furthermore, there were no correlations between log cord S-ferritin, placental weight, and newborns body weight (data not shown).

In the entire series of newborns, there was no correlation between log cord S-ferritin and length of gestation (r_s = 0.05, p = 0.6). In boys, there was no correlation between log cord S-ferritin and length of gestation (r_s = –0.11, p = 0.4), while girls displayed a significant positive correlation (r_s = 0.33, p = 0.021).

In newborns to iron treated mothers, log cord S-ferritin displayed positive correlations with length of gestation in both boys (r_s = 0.26, p = 0.14) and girls (r_s = 0.43, p = 0.027). In newborns to placebo treated mothers, log cord S-ferritin displayed a significant inverse correlation with length of gestation in boys (r_s = –0.36, p = 0.040), while girls demonstrated an insignificant positive correlation (r_s = 0.26, p = 0.2).

3.2.4 Cord serum transferrin saturation

TSAT values in newborns were normally distributed. In the entire series, values were arithmetic mean 58±19%; in newborns to iron treated mothers 58±19% and in newborns to placebo treated mothers 58±20% (Student’s t-test: p = 0.5). TSAT values in the entire series displayed no correlation with mothers TSAT or log S-ferritin prepartum. Newborns TSAT showed a positive correlation with newborns log S-ferritin (r = 0.46, p < 0.0001).

TSAT levels were not significantly different in boys vs girls (57±19% vs 60±20%, p = 0.4).

3.2.5 Cord serum erythropoietin

Cord S-EPO values became normally distributed after log transformation (Table 14). There was no correlation between Apgar scores and log cord S-EPO values neither in the entire series nor in the iron and placebo groups.

In the iron group, there was no difference between mothers prepartum log S-EPO (p = 0.24) and newborns log cord S-EPO (p = 0.24), while in the placebo group, mothers had significantly higher log S-EPO than newborns (p = 0.012).

No significant differences were found between log cord S-EPO in boys and girls or between log cord S-EPO in the iron and placebo groups (Table 14). In the whole series, there was a significant inverse correlation between log cord S-EPO and log cord S-ferritin (r = –0.35, p = 0.0007); however, there was no correlation in the iron group (n = 47, r = 0.04, p = 0.8) but a significant correlation in the placebo group (n = 44, r = –0.55, p = 0.0001).

Mother’s log S-EPO at 14–18- and 24–27 weeks gestation were not correlated to newborns log cord S-EPO. However, there were positive correlations between mother’s prepartum log S-EPO and newborns log cord S-EPO both in the whole series (r = 0.41, p = 0.0003), as well as in the iron group (r = 0.30, p = 0.053) and the placebo group (r = 0.44, p = 0.011).

4 Discussion

The number of tablets consumed was higher in the iron group than in the placebo group, which is an advantage for the study; it is probably due to the fact that iron supplements in the present dose may cause black stools, which may then motivate the participant to continue supplementation, realizing that she has been allocated to the “active” arm of the study.

4.1 Iron supplementation –effects on the mothers

The results of the present study clearly demonstrate that adequate iron supplementation during pregnancy improves iron status and reduces the frequency of ID and IDA both in the middle of gestation, prepartum, one week postpartum and even at 8 weeks postpartum. This is due to the fact, that even in the affluent Western European societies, preconception iron status is low in quite many women [5]. An overview of studies on iron supplementation in pregnancy has been given in a previous paper [2].

In the present study, comprising a population of whom the majority were rural, log S-ferritin concentration in the entire series at inclusion was 1.6476±0.3016 and 28% of the women had S-ferritin values below 30μg/L in early pregnancy. In the larger Danish study in 1995 [20], comprising pregnant women in an urban population, log S-ferritin concentration in the entire series at inclusion was 1.5090±0.2963 (Students t-test p < 0.0001) and 50% had S-ferritin values below 30μg/L in early pregnancy [20]. The difference between the two studies could rely on differences between dietary preferences in a rural vs urban population (higher meat intake in a rural population) or on general changes in dietary patterns over the time span of 10 years between the two studies, where the iron content of the general diet may have decreased concomitantly with a lower iron bioavailability. There are no national dietary surveys from the 1980’ties, but dietary iron intake in Danish women of reproductive age was median 9.7 mg/day in 2012, being distinctly below the recommended intake of 15 mg/day [21].

The differences in S-ferritin levels between the two studies are not due to differences in BMI. In the present study, median BMI was 20.7 kg/m² and 4.2% of the women were overweight (BMI > 28 kg/m²), while in the 1995 study, median BMI was significantly higher, 23.3 kg/m² and 6.8% of the women were overweight [20]. This finding is in accordance with the general increase in BMI in the Western populations during the last decades. However, there were no associations between S-ferritin levels and BMI in either of the two studies.

The positive effects on Hb levels both pre- and postpartum also indicate, that the frequency of postpartum anemia is markedly reduced by iron supplementation [7]. In the placebo group, 25% had anemia prepartum and 16% had anemia 8 weeks postpartum vs 0% and 3% in the iron group. As a consequence of the results of the present study, the Danish Health Authority have since 1992 recommended routine iron prophylaxis to all women during pregnancy, in doses of 40–50 mg elementary ferrous iron/day [22].

Postpartum ID and IDA appear to be major public health problems, e.g., in the USA, where approximately 13% of postpartum women are iron deficient and 10% have anemia (Hb < 120 g/L) [23]. Women from the low-income groups are at higher risk of iron deficiency compared to those in the high-income groups [1]. There is a lack of comprehensive studies concerning the frequency of postpartum anemia in the Nordic countries. In Denmark, the majority of women are discharged from the birth clinic a few hours after a normal delivery, leaving no time for a check of postpartum Hb. Furthermore, there is no consensus about the critical Hb value used in the definition of postpartum anemia [2]. Usually the World Health Organization’s (WHO) value for anemia in non-pregnant women is used as reference [2, 18].

Iron supplementation also had a significant positive impact on S-ferritin and TSAT levels. In the placebo group, 60% had ID prepartum and 16% had ID 8 weeks postpartum. TSAT levels were consistently higher in iron treated women, indicating a better supply of iron to the maternal and fetal tissues. Postpartum ID and IDA may have severe negative consequences for the mothers physical and mental well-being during lactation, which is an important period of the babies’ life.

Is the higher frequency of ID/IDA in placebo treated women of physiological importance? During pregnancy S-EPO increased significantly due to the accelerated erythropoiesis and there was a negative correlation between Hb and log S-EPO, especially in the placebo group. However, the S-EPO increase in the placebo group was generally higher than in the iron group, indicating a “normal” physiological response to the lower Hb levels, which may be due to ID/IDA.

One week postpartum, S-EPO levels decreased in both the iron and placebo group, indicating that 1) the physiological stimulus for the pregnancy-related increase in blood volume and erythrocyte volume had subsided, cardiovascular status returning to non-pregnant conditions and 2) that “normal” blood losses at delivery of 300–500 ml did not have any substantial impact on S-EPO levels.

Hb and log S-ferritin levels at weeks 14–18 showed significant correlations with levels at weeks 24–27 and levels prepartum, so in the clinical setting, Hb and S-ferritin levels in early pregnancy may be used as a guideline to give an estimate of the levels later in pregnancy.

4.2 Iron supplementation - effects on the newborns

While it appears straightforward to estimate the effects and advantages of iron supplementation on the mother’s iron status, the effects and advantages on the fetus/newborns are more complex and difficult to assess.

4.3 Erythropoietin

Current evidence indicates that EPO does not pass the placenta from the mother to the fetus [24) and that the placenta by itself does not secrete EPO in physiological amounts 25]. The S-EPO measured in the fetal circulation is consequently produced by the fetus itself, from early pregnancy in the fetal liver and in late pregnancy and after birth in fibroblasts in the renal cortex [26].

Dependent on the degree and duration of hypoxia during delivery, cord S-EPO may increase following birth. The frequency of hypoxia was low in this study, the newborns had a median Apgar score of 10 (range 7–10) 3 minutes after delivery and there was no correlation between scores and cord log S-EPO.

It is therefore surprising that we found distinct positive correlations between the mothers prepartum S-EPO and the newborns log cord S-EPO. Perhaps yet unidentified maternal factor(s), which can pass the placental barrier, having a regulatory effect on fetal EPO production, may play a role in this context.

In the whole series there was no significant difference between log cord S-EPO levels in the iron and placebo group. However, in the placebo group, there was significant correlation between log cord S-EPO and log cord S-ferritin, while such a correlation was absent in the iron group. This raises the question, whether this is just a random finding or may be a physiologic response to a “relative” ID in newborns in the placebo group.

4.4 Iron status

Cord S-ferritin levels in the present series were in accordance with the levels reported in a previous review paper [27]. The mechanisms between maternal-fetal iron transport have not been fully clarified. The absence of correlations between mothers and newborns iron status markers indicates that maternal-fetal iron metabolism to a certain degree takes its own course somewhat independently of mothers’ iron status. This independency may have a protective effect against development of severe ID in fetal life.

Iron supplementation had a significant impact on iron status by inducing an increase in cord S-ferritin levels, indicating higher body iron reserves in the iron group compared to the placebo group. This may be of benefit for the baby during the first year of life, especially during the 6-month lactation period, being recommended by the Danish Heath Authority, where the baby has a low dietary iron intake and must rely on its own body iron reserves.

Fetal brain development starts in early gestation and continues throughout pregnancy and childhood. It has been validated, that folate deficiency in early pregnancy, i.e., 15–30 days postconceptional, the so called “critical window”, may cause malformations with neural tube defects [28, 29].

As with folate, iron is essential for a normal development of the brain and ID alters brain development and functioning in an irreversible way [30, 31]. There may also be a “critical window” in the initial development of the fetal brain, where it is especially sensitive to ID, and this may have irreversible deleterious effects on the subsequent brain development both in fetal life and childhood.

Therefore, from an empiric point of view it seems crucial to maintain an adequate iron status and a sufficient iron supply to the fetus. This can be obtained by securing an adequate iron status in the mother by starting low dose iron supplementation with 30–40 mg elemental iron/day as ferrous fumarate or ferrous sulphate [20] or alternatively 25 mg elemental iron/day as ferrous bisglycinate [32]. According to the author’s opinion, iron supplementation should start as early as possible in pregnancy, and if pregnancy is planned, even in the preconception period –in analogy with the recommendations for folic acid supplementation [28, 29]. In Denmark, daily iron supplements have been recommended since 1992 [22] to start at the 10th week of gestation.

No other studies on iron supplementation during pregnancy have examined possible gender differences between iron status in the newborns. Somewhat surprisingly, we found higher cord S-ferritin values in girls than in boys, both in the entire series as well as in the iron and placebo group. Furthermore, in the entire series of boys, there was no correlation between cord S-ferritin and length of gestation, while girls displayed a significant positive correlation. However, in our subsequent dose-response study [20], there was no significant difference between cord S-ferritin levels in girls and boys, so further studies are needed to clarify, whether this gender difference is real or just a random finding.

Cord TSAT were much higher in newborns, compared to the values in mothers and showed a positive correlation with log cord S-ferritin, suggesting a high metabolic turnover of iron. There was no difference between TSAT levels in boys and girls. TSAT levels in the present study were in accordance with the levels previously reported in a review paper [27].

In newborns to iron treated mothers, log cord S-ferritin displayed positive correlations with length of gestation in both boys and girls, indicating that more iron was transferred to the fetus with increasing length of gestation, which appears to be a logical conclusion. This is consistent with the knowledge, that the iron content of the fetus increases with increasing length of gestation [33].

However, in newborns to placebo treated mothers, cord S-ferritin displayed a significant inverse correlation with length of gestation in boys, while girls demonstrated an insignificant positive correlation, suggesting that boys to placebo treated mothers may become iron depleted with increasing length of gestation, whereas girls have a greater ability to continue to accumulate iron, even during conditions with a poor iron supply from the mother. This may be a random finding, or it may be due to yet unknown gender differences in fetal iron metabolism, which need further investigation to clarify.

4.5 Anthropometrics

In pediatrics, anthropometric measures, e.g., birth weight, is frequently used as a proxy for the assessment of the outcome of a gestation. Anthropometric measures are also used as major endpoints in many interventional studies in pregnant women.

We found that birth weight was slightly, but not significantly higher in boys than girls, which is in accordance with present physiological knowledge. The difference may in part be due to the effect of androgens [34]. The statistical analyses showed that birth weight was strongly correlated to placental weight, length of gestation, mother’s body weight and BMI, but not mother’s Hb, S-ferritin or S-EPO at any time point during gestation.

This indicates that iron supplementation in the present dose of 66 mg elemental ferrous iron/day in ethnic Danish women had no significant influence on anthropometrics of the newborns. In our subsequent dose-response study [20], there were no associations between mothers S-ferritin and birth weight in women having a ferrous iron intake of 20–60 mg/day. Conversely, in women having an iron intake of 80 mg/day, S-ferritin displayed a significant negative correlation with birth weight (r_s = –0.38, p = 0.002) [20]. This finding raises the question, whether there is a maximum beneficial level for iron intake during pregnancy, which should not be exceeded.

Several epidemiological registry studies have shown that ID and anemia during pregnancy is associated with neurodevelopmental disorders, e.g., autism spectrum disorder, attention-deficit/hyperactivity disorder, and intellectual disability [35]. and presumably also with schizophrenia later in life [36, 37].

However, whether iron supplementation may have a positive influence on the development of fetal organs, e.g., the brain, which appears to be especially sensitive to certain vitamin/mineral deficiencies during fetal life, cannot be concluded from the design of the present study.

4.6 Length of gestation

The length of gestation and the placental weight were not influenced by iron supplementation, iron status or S-EPO of the mother or the gender of the newborns. It was not significantly different in iron and placebo treated mothers or in boys and girls.

5 Conclusions

Iron supplementation had a significant “positive” impact on the iron status and Hb levels of the pregnant women, both during pregnancy, but also up to at least 8 weeks postpartum, with a lower frequency of ID and IDA compared to placebo treated women. Iron supplementation also had a “positive” influence on newborns iron status. There was no impact of iron supplementation on the length of gestation, placental weight, or newborns birth weight. Birth weight was positively correlated only to mother’s body weight, placental weight, and length of gestation.

Newborn girls appeared to have higher cord S-ferritin levels than boys, both in the iron and placebo group –the reason for this difference is so far unknown.

Mothers prepartum log S-EPO values were positively correlated to newborns log cord S-EPO values, suggesting a maternal-fetal interrelationship or regulation.

The principal weakness of this detailed study is the relatively small number of participants. Also, due to randomization bias, the frequency of low Hb levels < 110 g/L at inclusion were different in the iron and placebo group. Taking iron tablets with meals significantly reduces intestinal iron absorption in pregnant women [20], but in the present study, we had no information on whether iron tablets were taken with meals or between meals.

Footnotes

Funding

This study was supported by Sundhedspuljen (grant no. 5910-32-1987 and 5910-264-1989) and Fonden for Lægevidenskabelig Forskning ved Sygehusene i Ringkøbing, Ribe og Sønderjyllands Amter,

Acknowledgments

The authors thank the Department of Clinical Chemistry, Bornholm Central Hospital, Roenne, Denmark, for analyses of serum ferritin and the Department of Clinical Chemistry, Bispebjerg Hospital, University of Copenhagen, Denmark for analyses of serum transferrin saturation.

Conflict of interest

The author declares no conflict of interest.

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