Prepregnancy Body Mass Index Shift Across Gestation: An Association with Breastfeeding Practices?

Abstract

Background:

Research has shown that mother's obesity and underweight are major risk factors for reduced initiation, duration, and exclusivity of breastfeeding.

Objective:

We compared breastfeeding practices from discharge until the third postnatal month in women, accounting to prepregnancy body mass index (BMI) and its shift across gestation.

Study Design:

Data on maternal shifts in BMI category from prepregnancy to gestational BMI by gestational weight gain (GWG) were defined according to 2009 Institute of Medicine (IOM) guidelines. Logistic regression models were estimated to assess the effect of prepregnancy and gestational BMI on breastfeeding, adjusting for clinically relevant factors.

Results:

The analysis included 658 women. According to prepregnancy BMI, 84 (12.8%) mothers were underweight, 444 (67.4%) were normal weight, 94 (14.3%) were overweight, and 36 (5.5%) were obese. Although in the range defined by IOM 2009, GWG shifted across the BMI categories in 445 (67.6%). Thus, while underweight women shifted in higher BMI categories, normal weight women category halved (230, 35%), and both overweight women (301, 45.7%) and obese women (127, 19.3%) tripled. Breastfeeding patterns at discharge, at first month, and at third month were comparable among prepregnancy and gestational BMI groups, except for prepregnancy BMI groups at third month (p 0.03). At multivariable analysis, neither prepregnancy BMI nor gestational BMI was associated with reduced exclusive breastfeeding within 3 months after discharge.

Conclusions:

Prepregnancy BMI and gestational BMI, in women with adequate GWG, do not affect exclusive breastfeeding initiation, duration, and exclusivity until the third month postpartum. Women need information and support to gain adequate weight during pregnancy.

Introduction

Adequate weight gain by prepregnancy body mass index (BMI) is important for optimal pregnancy outcomes and maternal health behaviors such as breastfeeding.^1,2 The Institute of Medicine (IOM) released new gestational weight guidelines (IOM, 2009)³ to reinforce those released in 1990, because many key aspects of women health of childbearing age have changed, such as the increasingly high rates of obese women among reproductive aged women, increasing gestational weight gain (GWG), increasing prevalence rate of underweight women in developed countries, and the increasing age of primiparous women becoming pregnant at late ages. The new guidelines changed the BMI categories to include underweight women with BMI <18.5 kg/m² and distinguished three progressive class of obese women with BMI values of 30–34.9 kg/m² (class I), 35–39.5 kg/m² (class II), and ≥40 kg/m² (class III). According to the new guideline, underweight women (BMI <18.5 kg/m²) should gain 12.5–18.0 kg during pregnancy, normal weight women (BMI 18.5–24.9 kg/m²) should gain 11.5–16.0 kg, overweight women (BMI 25.0–29.9 kg/m²) should gain 7.0–11.5 kg, and obese women (BMI ≥30 kg/m²) should gain only 5–9 kg. This is the standard for pregnancy weight gain worldwide.³ This is relevant, considering that despite the current epidemic obesity, underweight is widely common and both these extreme conditions are significant problems for women and their offspring during pregnancy, delivery, and puerperium.⁴ A low BMI in highly industrialized countries is not, in all probability, the result of environmental factors such as periodic food shortages and malnutrition. Excessive thinness has been glamorized among reproductive aged women, and unhealthy dieting to lose weight has become a popular practice in that age group. Body image in younger women is susceptible to society's influence through mass media and social networks.⁵

Understanding these associations in terms of maternal health and behavior is complex because BMI and GWG are also closely linked to lifestyle factors, diseases, and genetic traits that are also correlated with maternal, physiological, and social characteristics.^6,7 Weight gain during pregnancy is variable from woman to woman and pregnancy brings out a discrepancy between prepregnancy BMI and that at the end of pregnancy, moving one woman from a BMI range category to another.⁸ During this special period, conflicts about body changes, alterations in roles, additions of responsibility, and concerns about a woman's own mothering abilities are prevalent. Many of these concerns are also directly linked to puerperium, a period during which previously dormant psychological issues such as fears about physical changes, role adaptation, and psychosocial stress come to the surface, resulting of key importance for the psychology of lactation and behaviors such as breastfeeding initiation and discontinuation.⁹

A number of studies have found lower breastfeeding rates in obese women with respect to their normal-weight counterparts,^6,10 and there is a common misconception that maternal malnutrition greatly reduces the amount and the quality of milk that a mother produces.¹¹ These biological effects are, however, strongly influenced by confounding factors, such as maternal factors (i.e., gestational obesity, GWG, parity, age at childbearing, delivery mode, and/or socioeconomic status and habitus), which would be of particular importance not only for feeding decisions but also for short- and long-term breastfeeding outcomes.^12,13 However, again, evidence supporting this claim is lacking. To date, no published study has examined this issue from the perspective of maternal prepregnancy BMI or puerperae's GWG, and no studies have analyzed breastfeeding success, defined according to WHO¹⁴ in this population.

Therefore, the aims of our study were (i) to investigate the prepregnancy BMI and its shift across gestation, stratifying BMI and GWG according to 2009 IOM guidelines and (ii) compare breastfeeding practices from discharge until the third postnatal month in women, accounting to prepregnancy and gestational BMI categories.

Methods

All 764 women presenting at term of gestation at the maternity ward of Policlinico Abano Terme, Italy, between January 2015 and October 2015 were screened for the study inclusion.

Eighty-four mothers (9.9%) were ineligible because they were assuming prolactin inhibitors (5), did not speak Italian (56), did not expect a regular length of stay after delivery (11), had a serious chronic health condition (5), and/or their infant had health problems that complicated the newborn hospital stay (e.g., severe body weight loss or jaundice) (7). Among eligible mothers, 7 declined to participate and 15 were excluded due to incomplete data; thus, 658 mothers were included in the analysis.

An institutional review board (Policlinico Abano Terme) approved the protocol, and mothers gave their signed informed consent to be involved in the study and allowed access to their obstetric records.

Shifts of prepregnancy BMI category across gestation and GWG were calculated from self-reported maternal height, prepregnancy weight, and admission weight, which were extracted from the mother's obstetric records. Mothers' prepregnancy and gestational BMIs were classified according to the Centers for Disease Control and Prevention: underweight (<18.5 kg/m²), normal weight (18.5 to <25 kg/m²), overweight (25–29.9 kg/m²), and obese (>30 kg/m²).¹² Second, their total GWG was compared with the 2009 IOM, GWG guidelines for underweight (12–18 kg), normal weight (11.5–16 kg), overweight (7–11.5 kg), and obese (5–9 kg) women.³ Mothers were classified as gaining less, more, or within the recommended range for their prepregnancy BMI weight category.

According to standard maternity routines, all healthy newborns were placed skin-to-skin with their mothers immediately after birth. The newborn remained on the maternal chest until the first breastfeeding was established or until the newborn fell asleep. Usually the partner was present during and after childbirth. Rooming-in was practiced at the maternity ward. Our maternity rooms are created to facilitate an “at-home feeling” and allow parents to interact with their newborn. Skin-to-skin contact with the newborns and frequent breastfeeding are encouraged. In the absence of obstetric complications, maternity length of stay is scheduled at 36 hours after both a vaginal and a cesarean delivery.

Infant feeding data were recorded in accordance with the definitions of the World Health Organization (exclusive breastfeeding is defined as only maternal milk and nothing else; complementary breastfeeding is defined as a combination of breast milk and formula; and formula feeding is defined as offering exclusively bottle-fed formula).¹⁴

Breastfeeding patterns once discharged from the hospital were collected by a trained professional during the follow-up telephone interviews that were held 1 and 3 months later. At each interview, the mothers were asked to indicate with a yes/no response if they were breastfeeding exclusively, complementary, or by formula in last 24 hours.

Continuous data were expressed as median and interquartile range (IQR). Breastfeeding patterns (at discharge, at first month, and at third month) were compared between prepregnancy BMI groups and between gestational BMI groups using Fisher test with Bonferroni's adjustment for multiple comparisons. Logistic regression models were estimated to identify independent predictors of exclusive breastfeeding among prepregnancy BMI, gestational BMI and a set of clinically relevant factors (maternal age, nullparity, maternal education, working status, smoking and drinking habits, gestational age, GWG, mode of delivery, infant birth weight at discharge, and infant gender). A p-value <0.05 was considered statistically significant. Statistical analysis was performed using R 3.2.2 software (R Foundation for Statistical Computing, Vienna, Austria).¹⁵

Results

The study included 658 mothers with a median age of 33 years (IQR 30–37) and a median gestational age of 280 days (IQR 273–285). Mothers' and newborns' anthropometrical and clinical characteristics are shown in Table 1.

Table 1.

Demographic and Psychosocial Characteristics of Mother-Infant Dyads

	Prepregnancy	Gestational
Mothers, BMI
Underweight, <18.5 kg/m²	84 (12.8)	0
Normal weight, 18.5–24.9 kg/m²	444 (67.49)	231 (35.01)
Overweight, 25.0–29.9 kg/m²	94 (14.3)	301 (45.7)
Obese, >30 kg/m²	36 (5.5)	127 (19.2)
Age, years	33 (30–37)
Gestational age, days	280 (273–285)
GWG, kg	12 (10–15)
Parity^a
1	343 (52.9)
≥2	305 (47.1)
Delivery mode^b
Vaginal	461 (73.8)
Cesarean, elective	84 (13.4)
Cesarean, emergency	80 (12.8)
Educational level^c
Junior high school	70 (11.0)
High school	326 (51.1)
University	242 (37.9)
Smoking habits^d	47 (7.3)
Drinking habits^e	106 (16.5)
Marital status^f
Single	5 (0.8)
Married or living with the partner	628 (99.2)
Working status^a
Student	12 (1.8)
Housewife	71 (11.0)
Unemployed	66 (10.2)
Active worker	499 (77.0)
Birth weight, grams	3,350 (3,060–3,640)
Gender^g
Males	302 (46.8)
Females	344 (53.2)

Data expressed as n (%) or median (IQR).

Data not available in ^a10, ^b33, ^c20, ^d13, ^e15, ^f25, and ^g12 subjects.

BMI, body mass index; GWG, gestational weight gain.

According to prepregnancy BMI category, 84 women (12.8%) were underweight, 444 women (67.4%) were normal weight, 94 women(14.3%) were overweight, and 36 women (5.5%) were obese.

Overall median GWG was 12 kg (IQR 10–15) and according to the groups, 12 (10–14) kg in underweight women, 13 (11–15) kg in normal-weight women, 12 (9–14) in overweight women, and 7 (4–12) kg in obese women, according to 2009 IOM guidelines.³

At term of gestation prepregnancy BMIs shifted in 445 (67.6%) mothers, vanishing the underweight category during gestation, halving the normal weight (35.1%), and tripling the overweight (45.7%) and the obese (19.3%). In detail, among underweight women, 81/84 (96.4%) became normal weight and 3 (3.6%) became overweight. Among normal weight women, 149/444 (33.6%) remained normal weight, 270 (60.8%) became overweight, and 25 (5.6%) became obese. Among overweight women, 28/94 (29.8%) remained overweight and 66 (70.2%) became obese. Finally, all 36 (100%) obese women remained obese.

Breastfeeding practices, according to maternal prepregnancy and gestational BMI categories are reported in Table 2.

Table 2.

Univariate Analysis of Breastfeeding Pattern by Prepregnancy and Gestational Body Mass Index

Prepregnancy BMI	Underweight	Normal weight	Overweight	Obese	p^a
N	84	444	94	36	—
Breastfeeding at discharge					0.66
Exclusive	63 (75.0)	353 (79.5)	70 (74.4)	28 (77.8)
Complementary	13 (15.5)	68 (15.3)	12 (12.8)	5 (13.9)
Formula	8 (9.5)	23 (5.2)	12 (12.8)	3 (8.3)
Breastfeeding at 1st month					0.99
Exclusive	55 (65.5)	315 (71.0)	57 (60.7)	23 (63.9)
Complementary	16 (19.0)	71 (16.0)	16 (17.0)	7 (19.4)
Formula	13 (13.5)	58 (13.0)	21 (22.3)	6 (16.7)
Breastfeeding at 3rd month^a					0.03
Exclusive	42 (50.6)	273 (63.1)	46 (49.5)	17 (47.2)
Complementary	18 (21.7)	59 (13.6)	12 (12.9)	5 (13.9)
Formula	23 (27.7)	101 (23.3)	35 (37.6)	14 (38.9)
Gestational BMI	—				p^a
N	—	230	301	127	—
Breastfeeding at discharge	—				0.99
Exclusive		181 (78.7)	234 (77.8)	99 (78.0)
Complementary		35 (15.2)	47 (15.6)	16 (12.6)
Formula		14 (6.1)	20 (6.6)	12 (9.4)
Breastfeeding at 1st month	—				0.99
Exclusive		164 (71.3)	206 (68.4)	80 (63.0)
Complementary		37 (16.1)	51 (16.9)	22 (17.3)
Formula		29 (12.6)	44 (14.7)	25 (19.7)
Breastfeeding at 3rd month^b	—				0.21
Exclusive		133 (58.9)	180 (61.4)	65 (51.6)
Complementary		40 (17.7)	38 (13.0)	16 (12.7)
Formula		53 (23.4)	75 (25.6)	45 (35.7)

Data expressed as n (%).

Adjusted for multiple comparisons.

Data not available in 13 subjects.

BMI, body mass index.

Breastfeeding patterns at discharge, at first month, and at third month were comparable among prepregnancy and gestational BMI groups, except for prepregnancy BMI groups at third month (p 0.03).

However, at multivariable analysis, neither prepregnancy BMI nor gestational BMI was associated with reduced exclusive breastfeeding rate after discharge. Noteworthy, vaginal delivery significantly improved exclusive breastfeeding at discharge (odds ratio [OR] 1.87, 95% confidence interval [CI] 1.21–2.90), at first month (OR 1.68, 95% CI 1.12–2.52), and at third month (OR 2.02, 95% CI 1.37–2.98) with respect to cesarean delivery. Conversely, working mothers were more likely to provide exclusive breastfeed at discharge (OR 1.59, 95% CI 1.01–2.52), but not thereafter. Later age at delivery, instead, negatively affected exclusive breastfeeding at discharge (OR 0.94, 95% CI 0.90–0.98) and at first month (OR 0.94, 95% CI 0.91–0.98; Table 3).

Table 3.

Multivariable Analysis of Exclusive Breastfeeding

	At discharge		At 1st month		At 3rd month
Exclusive breastfeeding	p	OR (95% CI)	p	OR (95% CI)	p	OR (95% CI)
Prepregnancy BMI	0.67	—	0.12	—	0.07	—
Gestational BMI	0.83	—	0.27	—	0.55	—
Maternal age	0.009	0.94 (0.90–0.98)	0.003	0.94 (0.91–0.98)	0.10	—
Nulliparity	0.42	—	0.24	—	0.23	—
Maternal education	0.64	—	0.06	—	0.06	—
Active worker versus unemployed/student/housewife	0.04	1.59 (1.01–2.52)	0.12	—	0.38	—
Smoking habits	0.32	—	0.88	—	0.25	—
Drinking habits	0.26	—	0.20	—	0.17	—
Gestational age	0.55	—	0.48	—	0.87	—
GWG	0.18	—	0.55	—	0.43	—
Vaginal versus cesarean delivery	0.005	1.87 (1.21–2.90)	0.01	1.68 (1.12–2.52)	0.0004	2.02 (1.37–0.98)
Infant weight	0.07	—	0.57	—	0.40	—
Infant gender	0.08	—	0.95	—	0.62	—

BMI, body mass index; CI, confidence interval; OR, odds ratio.

Discussion

Prepregnancy BMI and GWG reflect maternal nutritional status and play a crucial role in creating an optimal intrauterine environment that contributes to improve pregnancy outcomes.^16,17 Understanding the relationship between prepregnancy and gestational BMI categories, their shifts mediated by GWG, and breastfeeding initiation, continuation, and exclusivity may also provide a basis for developing nutritional interventions that could improve breastfeeding and quality of life of growing infants.¹¹

In this study, performed in an industrialized area of North-Eastern Italy, characterized by late and low fertility, high education and occupation, and quite elevated caesarean section rates, we found a high prevalence of prepregnancy underweight women together with a low prevalence of obese women. Subsequently, despite a GWG respectful of the range recommended by 2009 IOM guidelines, prepregnancy BMI categories shifted in almost 70% mothers at term of gestation, enhancing the prevalence of high BMI categories. The prepregnancy underweight women disappeared and normal weight women halved, while overweight and obese women tripled at term of gestation. However, at multivariable analysis, neither prepregnancy underweight nor gestational obesity negatively affected breastfeeding initiation, duration, or exclusivity until the third month.

To our knowledge, this is the first study that, evaluating separately prepregnancy and gestational BMI categories, has shown that even women at the extreme range of BMI, obese, or underweight, who meet the recommended weight gain, are guaranteed for successful breastfeeding. Consequently, these findings highlight the need for antenatal education in pregnant women of any socioeconomic and demographic class, so that women with different prepregnancy or gestational BMIs, including underweight or obese women, can have successful breastfeeding once “optimal” GWG is guaranteed.

Over recent decades, accumulating evidence from all around the world has suggested that adequate GWG is positively associated with birth weight in the offspring and it is related to the risk of both low and high offspring birth weight.^18,19 This is relevant considering that women in Western countries are heavier than ever and being pregnant contributes even more to obesity.²⁰ Moreover, despite the current obesity world-wide epidemic, at the other end of the spectrum, in both low-income and industrialized countries, maternal underweight at first antenatal visit is common as well.²¹

The prevalence of underweight condition was only 3.1% of reproductive aged women in 2005–2006.²² The prepregnancy underweight category prevalence in this study (12.8%) is almost three times higher than prepregnancy obesity. The rate we found is consistent with other investigations in China (9.0%),²³ Sweden (9.6%),²⁴ and Japan (19.6–21.2%),² but it is much higher than that reported in the UK population (4.3%).²⁰ Not surprisingly, the prevalence of underweight is around 70% in India, Bangladesh, and Pakistan,²⁵ while in Africa, this proportion is 20–40%.^26,27

What is novel in this Italian cohort study is that underweight women had a mean weight gain within the IOM guidelines range and this gave no deleterious consequences for themselves or their infants, differently from what is usually reported in underweight and disadvantaged women living in low income countries.¹¹ In addition, in our series, almost 70% women changed BMI during gestation and the gestational obesity prevalence reached almost 20%, mainly due to the contribution of overweight women (70.2%).

Reduced breastfeeding rates among underweight and obese mothers is a matter of public health concern, as both these conditions are rising among women of reproductive age and the use of formula milk has been found to be at greater risk of obesity in childhood.²⁸ The mechanisms underlying these health issues remain, however, largely undefined because prepregnancy BMI, which is considered predictor of maternal nutritional status, and breastfeeding practice are closely linked to lifestyle, prevalent body image models, and sociocultural factors in industrialized countries,²⁹ whereas to endemic malnutrition, diseases, and genetic traits in disadvantaged, low-income countries.³⁰ In addition, when the IOM last revised the recommendations for weight gain during pregnancy,³ it emerged that a woman's nutritional status at conception may modify not only the course of pregnancy and its outcome but also the way her nutritional status changes during pregnancy.^31,32

The strengths of this study include the large sample size, the evaluation of both prepregnancy and gestational BMI, and the collection of breastfeeding data within the third month. In fact, this time span is clinically valuable because women with prepregnancy undernutrition or obesity who report specific nutritional problems during this interval could be targeted for additional support. Conversely, the limitations of the study are those characteristics of methodology because self-reported prepregnancy BMI is often underreported, especially among heavier women³³ However, the inclusion of both prepregnancy and gestational BMIs in the analysis should have reduced the potential bias. In addition, this study was performed at a single center in North-Eastern Italy and local population characteristics (i.e., obesity limited at class I and early weaning during the second trimester of life)³⁴ may limit the generalization of our findings.

In conclusion, we present evidence that pregnant women at extreme range of BMI need information and support to gain adequate weight during pregnancy to guarantee optimal feeding opportunities to their offspring. Understanding the complexity of such reciprocal relationships and adaptation differences surrounding BMI, GWG, and breastfeeding will provide a considerable challenge,³⁵ but it might also guide the clinical care and reduce suboptimal breastfeeding behavior.

Footnotes

Disclosure Statement

No competing financial interests exist

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