ABO blood group and risk of pre-eclampsia: A case-control study

Abstract

Background

It appears that some ABO blood groups may be a risk factor for venous thrombosis. The association between ABO group and risk of pre-eclampsia remains controversial. The purpose of this study was to evaluate the relationship between pre-eclampsia and ABO groups.

Methods

A retrospective case-control (1:2) study in a prospective monocentric registry including 20171 pregnancies was performed. Women with pre-eclampsia and severe pre-eclampsia were identified. Controls were matched according to age, parity, year of delivery and body mass index. Blood groups were considered.

Results

Two hundred fifty-three cases and 506 controls were included. No difference in distribution was found between cases and controls for non-O group (57.51% vs 62.56, p: 0.19), group A (39.92% vs 44.05, p: 0.29), group B (13.83% vs 15.42, p: 0.57) group AB (3.75 vs 3.08, p: 0.64). The analysis extended to severe pre-eclampsia showed no difference.

Conclusion

This study did not document any relationship between ABO groups and the risk of preeclampsia.

Keywords

Eclampsia hypertension pregnancy-induced pre-eclampsia

ABO blood groups have been documented to influence risk of thrombosis. In case of venous thromboembolism (VTE) non-O groups versus O-group were associated with an increased risk in male and female groups whether the episode was provoked, unprovoked or recurrent.¹ In the London database blood group study, non-O group was found to increase the incidence of VTE during pregnancy: the Odds Ratio (OR) versus O-group were 1.9 (95% CI [1.2–3.0]) for group A, 1.6 (95% CI [0.9–2.9]) for group B and 1.6 (95% CI [0.6–4.1]) for group AB.² In a case-control study conducted in Denmark the OR for VTE during puerperium compared with O-group were respectively 2.4 (95% CI [1.3–4.3]) for group A and 2.0 (95% CI [0.7–5.8]) for group AB; conversely no increased risk estimate was found for group B.³ Regarding the arteries, increased risks of cardiovascular diseases (CVD) have also been observed for non-O groups.¹ The association has been reported for myocardial infarction with group A and non-O groups^4–5 and stroke with group B.⁶ The severity of the coronary atherosclerosis was increased in the non-O groups.⁵

Higher levels of von Willebrand factors and Factors VIIIc are risk factors for VTE. Compared with O blood group subjects, non-O blood individuals have higher levels of these two factors.⁷ Thirty per cent of Factor VIII variance⁸ and 19% for von Willebrand factors⁹ variance were related to ABO groups.

Preeclampsia remains one of the major causes of maternal mortality and neonatal morbidity. The mechanisms of the disease appear to be multifactorial including thrombosis of the placental vasculature and an exaggeration of the physiological level of Von Willebrand factor. Identifying risk factors of pre-eclampsia is a cornerstone of pregnancy management.

Despite several studies, the relationship between ABO groups and pre-eclampsia is still controversial, hence this case-control study nested in a large prospective cohort.

Methods

The study population was retrospectively selected from a large prospective database including 20171 consecutive pregnancies followed between 2009 and 2016 in a tertiary care hospital, Hôpital de la mère et de l ‘enfant, Limoges, France. Maternal, fetal characteristics and events were collected.

Definitions

Pre-eclampsia was defined in case of systolic pressure ≥ 140mmHg and/or diastolic pressure ≥ 90mmHg on at least two measurements and proteinuria ≥ 300 mg/24 h after the 20th week of pregnancy. Severe pre-eclampsia was considered in case of pre-eclampsia associated with one or more of the following criteria: systolic blood pressure ≥ 160mmHg and/or diastolic blood pressure ≥ 110mmHg, oliguria 500 ml/24 h, creatinine ≥ 135 µmol/L, proteinuria > 3 g/24 h, pulmonary oedema, persistent abdominal pain, haemolytic anaemia, elevated liver enzymes, low platelets (HELLP) syndrome, neurological disorders (seizures, visual impairment, headaches), retroplacental haematoma.¹⁰ Miscarriages, stillbirths, neonatal deaths were considered as fetal losses. Birth weights <10th percentile were recorded.

Women in the control group were matched according to age (± 1 year), parity, body mass index (BMI) (± 1 kg/m²) and year of delivery. The ratio was one case for two controls.

Data collection

The data collected included age, country of birth, ABO and Rh groups. Obstetrical history was documented including parity, gravidity, previous pre-eclampsia, eclampsia, HELLP syndrome, gestational diabetes, hypertension during pregnancy, retro-placental haematoma. Cardiovascular risk factors (chronic hypertension, diabetes mellitus, smoking, renal insufficiency), previous history of venous thrombo-embolic disorders and thrombophilia were collected. BMI was calculated as weight/height² and rounded to one decimal place. Characteristics of the selected pregnancy were collected including medically assisted pregnancy, adverse events, mode and term of delivery. Information on the fetus and baby were obtained including vital status, gender, birth weight.

Statistics

The study was designed to study the relationship between ABO group and the occurrence of pre-eclampsia and severe pre-eclampsia. Continuous variables were presented as mean ± standard deviation (SD). Categorical variables were displayed by numbers and percentages. Distribution of the continuous variables were analysed with the Shapiro–Wilk method. For the continuous variables, statistical significance was evaluated by the Chi-square or Fisher test for categorical variables and by Student's t-test or Man and Whitney test ANOVA and Kruskal–Wallis tests were used to analyse continuous variables distribution as appropriate. A multivariate logistic regression model was performed to identify associated factors for pre-eclampsia and severe pre-eclampsia within variables when p-value <0.20 in univariate logistic regression. Interactions between independent variables in the final model were examined. A p-value <.05 was set for statistical significance. Statistical analyses were performed using Statview 9.1.3 (SAS institute, Cary, NC, USA).

Ethical approval

The current study was approved by the hospital ethical committee (24/05/2018).

Results

Between January 2009 and April 2016, 20171 consecutive pregnancies were prospectively included in the registry. Pregnancies of 253 women were complicated by pre-eclampsia or severe preeclampsia (Group 1). These women were matched with 506 controls (Group 2). Characteristic of both groups are shown in Table 1. Women were from multi-ethnic origin, the distribution was well balanced between the two groups, except for women from Maghreb who were more numerous in the control group. More women in the pre-eclampsia group presented a history of chronic hypertension or hypertension during a previous pregnancy. Conversely smoking was more prevalent in the control group. The characteristics of the pregnancies are presented in Table 2. Primigravida and women who had multiple pregnancies (twin) were more represented in Group 1. Term at delivery was shorter in case of preeclampsia and the mode of delivery was different with more caesarean deliveries. Regarding the neonates, in case of pre-eclampsia body weights were lower (Table 2).

Table 1.
Baseline characteristics of the subjects in the case and control groups.

Characteristics Controls (n = 506) Cases (n = 253) p

Age (years) 29.52 ± 5.57 29.47 ± 5.67 .925

Body mass index (kg/m²) 24.63 ± 4.53 24.65 ± 4.55 .957

Ethnicity, n (%) .113

Europe 368 (72.73%) 191 (75.49%) .414

Sub-Saharan Africa 21 (4.15%) 7 (2.77%) .340

Maghreb 56 (11.07%) 16 (6.32%) .003

Asia 12 (2.37%) 3 (1.18%) .268

Others* 18 (3.56%) 17 (6.72%)

Missing data 31 (6.13%) 19 (7.51%)

Medical history and maternal comorbidities, n (%)

Type 1 or 2 diabetes 5 (0.99%) 6 (2.37%) .132

High blood pressure 2 (0.4%) 18 (7.11%) < .0001

Chronic kidney disease 0 1 (0.4%) .157

Overweight/obesity 213 (42.09%) 104 (41.11%) .758

Venous thromboembolic disease/thrombophilia 17 (3.36%) 9 (3.56%) .887

Smoking, n (%)

History before pregnancy 169 (33.40%) 61 (24.11%) .012

Missing data 26 (5.14%) 24 (9.49%)

Smoking during pregnancy 104 (20.55%) 38 (15.02%) .080

Missing data 59 (11.66%) 43 (17%)

Obstetric history, n (%)

Hypertensive complications 9 (1.78%) 50 (19.76%) < .0001

Gestational diabetes 19 (3.75%) 12 (4.74%) .371

*South and Central America, Madagascar, Mauritius, Comoros, French Indies.

Table 2.
Characteristics of the pregnancies for case and control groups.

Characteristics Controls (n = 506) Cases (n = 253) p

Gravida, n (%) .049

Primagravid 229 (45.26%) 141 (55.73%)

Multigravid 277 (54.74%) 112 (44.27%)

Parity, n (%) .999

Nulliparous 330 (65.22%) 165 (65.22%)

Multiparous 176 (34.78%) 88 (34.78%)

Medically assisted procreation, n (%) 27 (5.34%) 21 (8.33%) .111

Missing data 1 (0.39%)

Number of fetuses, n (%) < .0001

Monofetal pregnancy 498 (98.42%) 227 (89.72%)

Multiple pregnancy 8 (1.58%) 26 (10.28%)

Maternal complications, n (%)

Gestational diabetes 39 (7.71%) 28 (11.07%) .088

Pregnancy outcome, n (%) .914

Child born alive 494 (97.63%) 248 (98.41%)

Spontaneous miscarriage 8 (1.58%) 2 (0.79%)

Termination of pregnancy 4 (0.79%) 2 (0.79%)

Missing data 1 (0.39%)

Weight of newborn (g) 3137 ± 620 2047 ± 826 p < .0001

Weight of newborn (percentiles) 45.3 ± 39.93 24.74 ± 25.58 p < .0001

Number of newborns (weight < 10th percentile) 7 26

Gestational age at delivery 38.99 ± 3.39 34.58 ± 3.82 p < .0001

Method of delivery, n (%) p < .0001

Vaginal delivery 392 (77.47%) 81 (32.02%)

Caesarean 112 (22.13%) 172 (67.98%)

Surgical termination of pregnancy 2 (0.4%) 0

No difference in blood group ABO distribution was observed between cases and controls (Table 3). Even if analysis were performed separately within the non-O group, there still was no difference. When considering severe pre-eclampsia, comparing a combined group non-O (A, B, AB) with group O gave the same results (Table 4).

Table 3.
Distribution of blood and rhesus groups between women with pre-eclampsia and controls.

Controls (n = 506) n (%) Pre-eclampsia (n = 227) n (%) p

Blood groups .550

O 215 (42.49) 85 (37.44) .199

Non-O 291 (57.51) 142 (62.56) .199

A 202 (39.92) 100 (44.05) .293

B 70 (13.83) 35 (15.42) .571

AB 19 (3.75) 7 (3.08) .649

Rhesus groups .943

Rh− 76 (15.02) 37 (14.62)

Rh+ 430 (84.98) 216 (85.38)

Table 4.
Distribution of non-O blood groups between women with severe pre-eclampsia and controls.

Blood groups n (%) Controls (n = 506) Severe pre-eclampsia (n = 104) p

O 215 (42.49%) 35 (33.65%) .095

Non-O 291 (57.51%) 69 (66.35%) .095

The representativeness of the population was evaluated through a comparison between ABO groups distribution in the control group and the French general population. Overall, the ABO groups distribution was similar except for B group which was over-represented in the control group, the same analysis was conducted with the cases group with similar results (table 5).

Table 5.
Distribution of blood groups between cases, controls and the general population.

Blood groups n (%) Controls (n = 506) General population (n = 67,186,638) P

O 215 (42.49%) 28 218 388 (42%) .823

Non-O 291 (57.51%) 38 968 250 (58%) .823

A 202 (39.92%) 29 562 121 (44%) .065

B 70 (13.83%) 6 718 664 (10%) .004

AB 19 (3.75%) 2 687 465 (4%) .778

Blood groups n (%) Cases (n = 253) General population (n = 67,186,638) p

O 95 (37.55%) 28 218 388 (42%) .151

Non-O 158 (62.45%) 38 968 250 (58%) .151

A 111 (43.87%) 29 562 121 (44%) .967

B 39 (15.42%) 6 718 664 (10%) .004

AB 8 (3.16%) 2 687 465 (4%) .496

Discussion

We did not demonstrate any difference in the ABO group distribution between the pre-eclampsia group and controls. Our results are in accordance with previous studies. However the relationship is still matter of debate. In a large retrospective cohort study conducted in Sweden¹¹ women with blood group AB and RhD positive have the highest risk of pre-eclampsia and severe pre-eclampsia. However the analysis was not adjusted for parity. Two other retrospective cohort analysis documented no significant positive association between groups O and A¹² or O RhD+¹³ and pre-eclampsia. In the other cohort analysis, such a link was not described.^14–17 Most of the case-control studies^18–23 did not demonstrate any association between ABO groups and the risk of pre-eclampsia, however the contrary was concluded in five studies. In the last ones, the results were divergent. In the study conducted by Pearse²⁴ an association between pre-eclampsia and group O was described, conversely for Amin et al.²⁵ the representation of group O subjects in the cases was lower. Two studies documented a positive association between severe pre-eclampsia and group A²⁶ and group AB.²⁷ In another case-control study²⁸ an association between group AB and pre-eclampsia appeared. Differences in cases definition might influence the comparison of these five studies. Clark and Wu ²³ meta-analysis including 17 studies gave negative results. In the meta-analysis conducted by Franchini²⁹ non-O groups were associated with pre-eclampsia, however prevalence of group O in the studies included were from 21 to 48% in the cases and 32 to 48% in the controls suggesting an heterogeneity in the ethnical representation.

The strength of our study lies on our controls matching criteria. Indeed, controls were adjusted with cases on age, BMI, parity, and year of pregnancy. These criteria were selected according to the results of two studies^30–31 analysing risk factors associated with pre-eclampsia. The first one was a meta-analysis³⁰ including 25,356,688 pregnancies. Relative risks associated with age >35 yrs or 40 yrs and BMI > 25 kg/m² or >30 kg/m² were respectively 1.2 (95% CI [1.1–1.3]), 1.5 (95% CI [1.2–2.0]), 2.1 (95% CI [2.0–2.2]), 2.8 (95% CI [2.6–3.1]) and nulliparity 2.1 (95% CI [1.9–2.4]). The influence of BMI was reported in a multicentric study including 2637 pregnancies, adjusted OR for BMI > 35–40 were 3.6 (95% CI [2.1–6.0]).³¹ In the previous case-control studies adjustment were limited to age and parity¹⁹ or ethnicity.¹⁶ Pre-eclampsia definition was variable in the different studies and sometimes a formal definition was not available, our criteria were in accordance with the ACOG recommendations.¹⁰ Regarding the distribution of ABO group in the general population there is no difference between male or female. In a study including 45,925 French women dedicated to the relationship between ABO groups and dyslipidemia the frequencies were respectively for groups O, A, B and AB: 44%, 43%, 9% and 4%.³²Last our results were in accordance with a case-control study conducted in Mexico.³³ In nulliparous pregnant women, after adjustment on maternal age, pre pregnancy overweight/obesity, mean blood pressure at the first antenatal visit, multiple gestation, aspirin prescription and fetal sex, ABO groups were not associated with a pre-eclampsia risk.

Besides, we performed the same analysis among the sub-group of pregnancies complicated by severe pre-eclampsia, similar conclusions were withdrawn with no difference in ABO blood group repartition.

However, our study has limitations. The ABO group distribution in the control group was different from the French general population. Group B was over-represented. Even if we did not describe any relationship between ABO groups and pre-eclampsia, extrapolation of the results to other population might be limited. About one-quarter of our population was from a non-European origin. We did not take into account the ethnicity in the adjustment. However, with the exception of women from Northern African origin, we did not document any difference of origin between Groups 1 and 2. Due to the limited number of cases we did not perform any adjustment on history of chronic or pregnancy induced hypertension and diabetes. Nulliparity and BMI had the greatest population attributable fraction for pre-eclampsia in a large meta-analysis.³⁰ Thus, parity and BMI were selected according these results.

Conclusion

Despite of the role of ABO groups in VTE and arterial diseases, the current study did not show any evidence of a relationship with pre-eclampsia. Our findings do not support any influence of ABO groups in identifying women at risk of pre-eclampsia even in its severe manifestations.

Characteristics	Controls (n = 506)	Cases (n = 253)	p
Age (years)	29.52 ± 5.57	29.47 ± 5.67	.925
Body mass index (kg/m²)	24.63 ± 4.53	24.65 ± 4.55	.957
Ethnicity, n (%)			.113
Europe	368 (72.73%)	191 (75.49%)	.414
Sub-Saharan Africa	21 (4.15%)	7 (2.77%)	.340
Maghreb	56 (11.07%)	16 (6.32%)	.003
Asia	12 (2.37%)	3 (1.18%)	.268
Others*	18 (3.56%)	17 (6.72%)
Missing data	31 (6.13%)	19 (7.51%)
Medical history and maternal comorbidities, n (%)
Type 1 or 2 diabetes	5 (0.99%)	6 (2.37%)	.132
High blood pressure	2 (0.4%)	18 (7.11%)	< .0001
Chronic kidney disease	0	1 (0.4%)	.157
Overweight/obesity	213 (42.09%)	104 (41.11%)	.758
Venous thromboembolic disease/thrombophilia	17 (3.36%)	9 (3.56%)	.887
Smoking, n (%)
History before pregnancy	169 (33.40%)	61 (24.11%)	.012
Missing data	26 (5.14%)	24 (9.49%)
Smoking during pregnancy	104 (20.55%)	38 (15.02%)	.080
Missing data	59 (11.66%)	43 (17%)
Obstetric history, n (%)
Hypertensive complications	9 (1.78%)	50 (19.76%)	< .0001
Gestational diabetes	19 (3.75%)	12 (4.74%)	.371

Characteristics	Controls (n = 506)	Cases (n = 253)	p
Gravida, n (%)			.049
Primagravid	229 (45.26%)	141 (55.73%)
Multigravid	277 (54.74%)	112 (44.27%)
Parity, n (%)			.999
Nulliparous	330 (65.22%)	165 (65.22%)
Multiparous	176 (34.78%)	88 (34.78%)
Medically assisted procreation, n (%)	27 (5.34%)	21 (8.33%)	.111
Missing data		1 (0.39%)
Number of fetuses, n (%)			< .0001
Monofetal pregnancy	498 (98.42%)	227 (89.72%)
Multiple pregnancy	8 (1.58%)	26 (10.28%)
Maternal complications, n (%)
Gestational diabetes	39 (7.71%)	28 (11.07%)	.088
Pregnancy outcome, n (%)			.914
Child born alive	494 (97.63%)	248 (98.41%)
Spontaneous miscarriage	8 (1.58%)	2 (0.79%)
Termination of pregnancy	4 (0.79%)	2 (0.79%)
Missing data		1 (0.39%)
Weight of newborn (g)	3137 ± 620	2047 ± 826	p < .0001
Weight of newborn (percentiles)	45.3 ± 39.93	24.74 ± 25.58	p < .0001
Number of newborns (weight < 10th percentile)	7	26
Gestational age at delivery	38.99 ± 3.39	34.58 ± 3.82	p < .0001
Method of delivery, n (%)			p < .0001
Vaginal delivery	392 (77.47%)	81 (32.02%)
Caesarean	112 (22.13%)	172 (67.98%)
Surgical termination of pregnancy	2 (0.4%)	0

	Controls (n = 506) n (%)	Pre-eclampsia (n = 227) n (%)	p
Blood groups			.550
O	215 (42.49)	85 (37.44)	.199
Non-O	291 (57.51)	142 (62.56)	.199
A	202 (39.92)	100 (44.05)	.293
B	70 (13.83)	35 (15.42)	.571
AB	19 (3.75)	7 (3.08)	.649
Rhesus groups			.943
Rh−	76 (15.02)	37 (14.62)
Rh+	430 (84.98)	216 (85.38)

Blood groups n (%)	Controls (n = 506)	Severe pre-eclampsia (n = 104)	p
O	215 (42.49%)	35 (33.65%)	.095
Non-O	291 (57.51%)	69 (66.35%)	.095

Blood groups n (%)	Controls (n = 506)	General population (n = 67,186,638)	P
O	215 (42.49%)	28 218 388 (42%)	.823
Non-O	291 (57.51%)	38 968 250 (58%)	.823
A	202 (39.92%)	29 562 121 (44%)	.065
B	70 (13.83%)	6 718 664 (10%)	.004
AB	19 (3.75%)	2 687 465 (4%)	.778
Blood groups n (%)	Cases (n = 253)	General population (n = 67,186,638)	p
O	95 (37.55%)	28 218 388 (42%)	.151
Non-O	158 (62.45%)	38 968 250 (58%)	.151
A	111 (43.87%)	29 562 121 (44%)	.967
B	39 (15.42%)	6 718 664 (10%)	.004
AB	8 (3.16%)	2 687 465 (4%)	.496

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Philippe Lacroix

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