Fetal Sex and Risk of Preeclampsia: Dose Maternal Race Matter?

Abstract

Objective

To examine whether maternal race could affect the relationship between fetal sex and preeclampsia.

Material and Methods

This study was a cohort analysis using prospectively collected data from pregnant women who participated in the Vitamin Antenatal Asthma Reduction Trial (VDAART). Preeclampsia was the secondary outcome of VDAART. We examined the association of fetal sex with preeclampsia and its potential interaction with maternal race in 813 pregnant women (8% with preeclampsia) in logistic regression models with adjustment for preterm birth (<37 weeks of gestation), maternal age, education, and body mass index at enrolment and clinical center. We further conducted a race stratified analysis and also examined whether any observed association was dependent on the gestational age at delivery and prematurity.

Results

In an analysis of all races combined, preeclampsia was not more common among pregnant women with a male fetus compared to those with a female fetus (odds ratio [OR] 1.3, 95% CI 0.81, 2.24). There was an interaction between African American race and fetal sex in association with preeclampsia after adjustment for preterm delivery and other potential confounders (P=0.014). In race stratified analyses, we observed higher odds of preeclampsia among African American pregnant women who carried male fetuses after adjustment for preterm delivery and other potential confounders (adjusted OR 2.4, 95% CI 1.12, 5.60).

Conclusion

We observed fetal sexual dimorphic differences in the occurrence of preeclampsia in African American women, but not in Whites. Information on fetal sex may ultimately improve the prediction of pre-eclampsia in African American mothers, who might be at higher risk for this adverse condition in pregnancy.

INTRODUCTION

Preeclampsia is a complex hypertensive disorder of pregnancy that causes maternal and fetal morbidity and mortality.[1] Preeclampsia could affect up to 8% of pregnancies.[2] The etiology of the disorder is not fully understood, yet it is known that pathobiological processes are compounded by the interactions at the maternal-fetal interface and environmental exposures.[3] While many studies of pre-eclampsia seek to identify modifiable risk factors, recognition of non-modifiable factors, such as maternal race and fetal sex, could be equally important, given their potential to improve screening algorithms for this adverse condition in pregnancy. A better understanding of all types of risk factors will also aid our understanding of the underlying mechanisms that contribute to preeclampsia.

It is known that racial disparities contribute to maternal morbidity including preeclampsia. Several studies have investigated the relationship of fetal sex with the risk of preeclampsia development; however, their results are not consistent. While some studies did not find an association, others reported either female or male fetal sex as a risk factor. [4,5] A meta-analysis of data from 11 prior studies of pregnant women from Europe, Oceania, and the US suggested an effect of gestational age on the relationship of fetal sex with preeclampsia.[5] While the study observed no differences in the distribution of female versus male fetuses in the overall occurrence of preeclampsia, additional results showed female preterm preeclampsia was more prevalent than male preterm preeclampsia (<34 and <37 weeks of gestation; OR 1.1, 95% CI: 1.02, 1.21 and OR 1.4, 95% CI: 1.17, 1.59, respectively).[5]

In a recent report with the inclusion of substantially more subjects, Jaskolka and colleagues conducted a systematic review and meta-analysis of the studies on the relationship between fetal sex and risk of preeclampsia during pregnancy.[4] In this investigation, the authors qualified 22 prior investigations for the inclusion in the analysis. The pooled analysis of these studies did not demonstrate an association between fetal sex, either male or female, with the risk of preeclampsia development. However, meta-regression followed up by a sensitivity analysis demonstrated an impact of race on the relationship of fetal sex and preeclampsia such that male fetal sex in the non-Asian population was associated with an increased risk of preeclampsia (RR 1.05, 95% CI 1.03, 1.06).[4] One major limitation of this study was reporting only pooled unadjusted estimates and lack of accounting covariates possibly associated with preeclampsia such as maternal age, body mass index (BMI), and gestational age at delivery..

Given the contrasting results in this context and the fact that meta-analysis cannot improve the quality of the original studies, we examined the relationship between fetal sex and preeclampsia using the data from Vitamin D Antenatal Asthma Reduction Trial (VDAART). We hypothesized that maternal race is a determinant factor in the association of fetal sex and preeclampsia. We further investigated whether any observed association was dependent on the gestational age at delivery.

MATERIAL AND METHODS

Study population and design

VDAART was a randomized, double-blind, placebo-controlled clinical trial of vitamin D supplementation (4000 International Units Vitamin D plus a multivitamin with 400 IU Vitamin D daily) versus placebo (placebo pill plus a multivitamin with 400 IU vitamin D daily) in pregnant women to prevent the development of pregnancy complications, such as preeclampsia and asthma or atopy in their children by age of 3 years.[6] Eligible participants in the VDAART were non-smoking, pregnant women aged 18–39 years at 10–18 weeks of gestation; with a personal history of asthma or atopy or partner’s history of asthma or atopy. Chronic hypertension was an exclusion criterion in the VDAART.[7]

Ethics approval

The VDAART protocol was approved by the Institutional Review Boards of the three participating study sites and of the data coordinating center, the Channing Division of Network Medicine at Brigham and Women’s Hospital, Boston, Massachusetts, USA. All participants consented to participate in the trial. The results for the outcome of preeclampsia are published and this study is an ancillary study to the primary report and using the intent-to-treat (ITT) population.[2] In brief,

Vitamin D supplementation initiated in weeks 10–18 of pregnancy did not reduce preeclampsia incidence in the intention-to-treat paradigm. However, vitamin D levels of 30 ng/ml or higher at trial entry and in late pregnancy were associated with a lower risk of preeclampsia.[2] A secondary usage of the data for all ancillary studies including this study was also approved the Institutional Review Boards.

Main outcome: Preeclampsia diagnosis

After delivery, medical records were abstracted, and a committee of 4 board-certified obstetricians conducted a blinded review of 276 abstracted charts of subjects with a noted diagnosis of hypertension, proteinuria, or preeclampsia to determine preeclampsia status. The diagnosis of preeclampsia at the time of the record reviews was based on the definition of preeclampsia by the 2013 Task Force on Hypertension in Pregnancy [8], which included the identification of high blood pressure (BP) and either proteinuria (≥300 mg per 24-hour collection or ≥1+ on a urine dipstick) or the presence of elevated liver enzymes, high platelet count, headache, or visual disturbances after 20 weeks of gestation. High BP was diagnosed for participants who had a systolic BP at or above 140 mmHg, a diastolic BP at or above 90 mmHg, or both, with a second elevated measurement, noted in the medical record at least 4 hours after the first measurement was taken.[2]

Main exposures and additional study variables

Maternal race and fetal sex status were the main exposures of interest. Additional study variables were selected as a priori determinants or potential confounders in the relationship of the preeclampsia and main variables of interest: gestational age at delivery, maternal BMI at enrollment, maternal age, maternal education, maternal asthma, and study site. Completed questionnaires at enrollment and monthly thereafter as well as a review of medical records provided the information on the variable of interests.

Statistical analysis

The main study groups were pregnancies with and without preeclampsia. For the comparison of baseline characteristics between maternal subjects with and without preeclampsia, we used the Student’s t-test and chi-square or Fisher’s exact test, as appropriate. The analysis was performed in three steps. First, we assessed the risk of preeclampsia in relationship with fetal sex status, regardless of the maternal race. Secondly, we examined the potential of interaction between maternal race and fetal sex in association with preeclampsia and how the association of fetal sex with preeclampsia might differ according to maternal race (White, African American, and Others). Thirdly, we examined whether an observed association would be independent of preterm delivery status or any other potential confounders in the relationship between fetal sex and preeclampsia.

We used multivariable logistic regression to evaluate whether an observed risk of preeclampsia was independent of gestational age at delivery. Regression models were adjusted for covariates and potential confounders as noted previously. Crude and adjusted odds ratios (OR and aOR) were calculated with 95% confidence intervals (CI) and corresponding P-values were obtained. All statistical analysis was performed using the R statistical package version 3.6.2. All tests were two-sided and a P-value less than a prespecified alpha of 0.05 was considered statistically significant.

RESULTS

Study population

Figure 1 provides the study participant flowchart. The VDAART ITT population of enrolled subjects included 816 pregnant women at 10–18 weeks of gestation, of whom 67 women (67/816 = 8.2%) had preeclampsia during their pregnancies. Maternal race and fetal sex status were available for 813 subjects (66 with preeclampsia). Table 1 presents the pregnant women’s characteristics according to their preeclampsia status. The distribution of race was not different between pregnant women with and without preeclampsia. Among other baseline characteristics, women who developed preeclampsia during their pregnancies were relatively younger (at enrollment) than those who did not develop preeclampsia. (mean difference −1.80 years, 95% CI −0.50, −3.13; Table 1). Similarly, women with preeclampsia had a lower gestational age at delivery relative to those without preeclampsia (−1.16 weeks, 95% CI −0.36, −1.97). The pregnant women who developed preeclampsia also had higher BMI at enrollment compared to those with uncomplicated pregnancies (3.11 mg/kg², 95% CI 1.05, 5.16). No difference in the frequency of preeclampsia was observed among White, African American, and Other races (6.4% [21/328], 11% [35/318], and 7.6% [10/132], respectively; Table 1).

Figure 1.

The VDAART participants and ancillary study cohort.

Table 1.

Characteristics of VDAART study population (N=813) by preeclampsia status^a

	Preeclampsia	Without Preeclampsia	P-value
	(n=66)	(n=747)
Fetal sex: male	39 (59.1)	387 (51.81)	0.31
Maternal age (mean, SDb)	25.70 (5.12)	27.5 (5.51)	0.007
Maternal race			0.39
Black	35	318
White	21	307
Other	10	122
Gestational age at delivery (weeks)
mean (SD)	37.76 (3.23)	38.92 (2.02)	0.005
Less than 37	18 (27.27)	57 (7.73)	<0.001
Maternal income			0.73
Less than <$50,000	28 (41.79)	315 (42.06)
$50,000 or greater	18 (26.87)	256 (34.18)
Prefer not to answer or do not know	21 (31.34)	178 (23.76)
Maternal education			0.01
Less than college	38 (57.58)	307 (41.10)
Some college, college graduate or graduate school	28 (42.42)	440 (58.90)
Maternal asthma: yes	28 (42.42)	297 (39.76)	0.77
Site name			0.013
San Diego	17 (25.76)	260 (34.81)
Boston	14 (21.21)	226 (30.25)
St. Louis	35 (53.03)	261 (34.94)
Maternal race			0.39
Black	165 (51.6)	225 (47.0)
White	98 (30.6)	167 (34.9)
Other	57 (17.8)	87 (18.2)
Body mass index at enrollment
mean (SD)	31.78 (7.97)	28.67 (7.58)	0.003
Less than 25 kg/m2	15 (22.73)	267 (35.74)	0.025
Number of pregnancies			0.35
1st	27 (40.9)	257 (34.4)
2nd or more	39 (59.1)	490 (63.6)
Severe preeclampsia: yes	12 (18.18)	-	-
Gestational hypertension: yes	-	55 (7.36)	-

^aData are given as number (percentage) of individuals per study group unless otherwise specified.

^bAbbreviations: SD - standard deviation; kg: kilogram

Relationship of fetal sex with preeclampsia and the effect of maternal race status

Regardless of maternal race, having a fetus with male sex in pregnant women was not significantly associated with increased odds of preeclampsia compared with having a female fetus (1.3, 95% CI 0.81, 2.24, Table 1). However, there was an interaction between African American race and fetal sex in association with preeclampsia after adjustment for preterm delivery and other potential confounders (P=0.014). Hence, we conducted the stratified analysis by maternal race.

The stratified analysis by maternal race did not find an association between fetal sex and maternal preeclampsia status among White pregnant women and those with races other than White or African American (OR 0.8, 95% CI 0.33, 1.98; OR 0.6, 95% CI 0.17, 2.32, respectively; Table 2). Adjustment for potential confounders including preterm delivery (<37 weeks of gestation), BMI (kg/m²) and maternal age at enrollment, maternal education (college or graduate vs below college) and study center did not significantly change the observed associations (aOR 0.7, 95% CI 0.24, 1.73; aOR 0.7, 95% CI 0.15, 3.0, respectively; Table 2). However, we observed higher odds of preeclampsia development among African American pregnant women who carried male fetuses as compared to those who carried female fetuses (OR 2.4, 95% CI 1.15, 5.41). The observed higher odds of preeclampsia were independent of preterm delivery (<37 weeks of gestation), BMI (kg/m²), maternal age at enrollment, maternal education (college or graduate vs below college), and study center (aOR 2.4, 95% CI 1.12, 5.60; Table 2).

Table 2.

Risk of preeclampsia by fetal sex stratified by maternal race; A. maternal race: White, B. maternal race: Black/African American, and C. maternal race: Other^a

A.
	Maternal Preeclampsia Status			Maternal Preeclampsia Risk		P-value
	Yes	No		OR (95% CI)	Adjusted ORb (95% CI)
Fetal Sex
Female	11	145	156	Reference	Reference
Male	10	162	172	0.81 (0.33, 1.98)	0.66 (0.24, 1.73)	0.40
Total	21	307	328
B.
	Maternal Preeclampsia Status			Maternal Preeclampsia Risk		P-value
	Yes	No		OR (95% CI)	Adjusted OR# (95% CI)
Fetal Sex
Female	10	156	166	Reference	Reference
Male	25	162	187	2.41 (1.15, 5.41)	2.41 (1.12, 5.60)	0.03
Total	35	318	353
C.
	Maternal Preeclampsia Status			Maternal Preeclampsia Risk		P-value
	Yes	No		OR (95% CI)	Adjusted OR# (95% CI)
Fetal Sex
Female	6	59	65	Reference	Reference
Male	4	63	67	0.62 (0.17, 2.32)	0.70 (0.15, 3.0)	0.63
Total	10	122	132

^aAsian, American Indian or Alaskan, Native Hawaiian

^bOdds Ratio (OR) and 95% Confidence Interval (CI) are adjusted for preterm delivery (<37 weeks of gestation), body mass index (BMI, kg/m²) at enrollment, maternal age at enrollment, maternal education (college or above vs below college) and study center.

DISCUSSION

This study contributes to the existing literature as it demonstrates that the relationship between fetal sex and risk of preeclampsia development could vary by maternal race. More specifically, our finding shows that African American pregnant women carrying fetuses with male sex (vs. female sex) might have two times higher risk of developing preeclampsia during their pregnancies. Furthermore, this association was independent of gestational age and preterm delivery of the offspring. Information on fetal sex may ultimately improve the prediction of preeclampsia in African American mothers, who might be at higher risk for this adverse condition in pregnancy.[9,10]

Our findings are more aligned with the Jaskolka and colleagues’ study that suggested a higher risk of preeclampsia in pregnant women who carried male fetuses[4] but are distinguished to observe the association among African American women, a subgroup of non-Asian women. Several factors might have contributed to the conflicting results in the literature on the relationship between fetal sex and the risk of preeclampsia during pregnancy.[4,5] One major factor could be the variability in the guideline definitions of preeclampsia and its subtypes that have also been changed in the past decades. These changes highlight the importance of identification of pregnancy-related biomarkers that could assist in diagnosing different subtypes of preeclampsia and the efficacy of applied treatments,[11] as well as differentiating the condition from other adverse pregnancy disorders at an earlier stage of pregnancy.[12] More importantly, the consistency of these biomarkers across different populations and races should be further explored. This approach could also help with the characterization of preeclampsia phenotypes during the pre-clinical stage and early placental development and whether these phenotypes might display fetal sexual dimorphism.[13]

Another important factor is the differences in population demographics and risk factor profiles for preeclampsia that might also affect its clinicopathological presentation. For example, glomerular capillary endotheliosis, a characteristic glomerular lesion in preeclampsia [14], was not observed in 15% and 40% of primiparous and multiparous pregnant women with preeclampsia, respectively.[15] Chronic hypertension is more prevalent and less controlled among black women.[16] The characteristics of each population and the change in risk profiles along with secular trends in the epidemiology of preeclampsia could have affected the results from prior observations that investigated the association of fetal sex and preeclampsia.[17]

Pregnancy is characterized by substantial alterations in maternal immune responses to induce fetal tolerance throughout pregnancy. During pregnancy, there is a greater production of certain proinflammatory cytokines [18,19], owing to an interaction between the decidual immune cells and trophoblast cells as well as the release of syncytiotrophoblast microparticles into the mother’s circulation in the first trimester and later in pregnancy, respectively.[19,20] In women who develop preeclampsia, these cytokine productions, as well as innate and adaptive immune responses, are exaggerated or imbalanced (proinflammatory cytokines of TNF-α, IL-6, and IL-10, a decrease in Th2 cells and an increase in Th17 cells).[21–23]

Could maternal immune responses vary among African American women? Few biological data are available but suggest pregnancy-associated immune responses could vary considerably by maternal race. During pregnancy and non-pregnancy, African American women were shown to have a higher susceptibility to stress-induced immune dysregulation compared to Whites.[24,25] More specifically, African American women demonstrated higher stress-induced IL-6 response compared to Whites.[24,26] Black women were also reported to be at higher risk for severe morbidity and mortality associated with preeclampsia.[27] However, whether maternal immune responses among African Americans as compared with other races could also vary by fetal sex is a matter of further investigation.

Could fetal sex affect maternal immune responses differently by race? While there are no investigations on this matter, few studies suggest the effect of fetal sex on the maternal immune response. Here, we review some of the biological evidence. Mitchell and colleagues observed no differences in serum cytokine levels based on the fetal sex among 80 pregnant women (46 with male fetuses).[28] However, the authors demonstrated that pregnant women carrying females exhibited greater production of IL-6 in early and late pregnancy, TNF-α in early pregnancy, and IL-1β in mid and late pregnancy after an immune challenge by lipopolysaccharide (LPS) stimulation.[28] In a randomly selected case-control study (N=648, 216 with preeclampsia), Taylor et al. found that female fetal sex was inversely associated with proinflammatory IFNγ and IL-12 in the first trimester of singleton, primiparous pregnancies.[29]

However, the authors did not observe any differences in the relationship between fetal sex and immune markers comparing pregnancies with and without preeclampsia. In contrast, female fetal sex was associated with increased second-trimester proinflammatory (TNFβ and IL-1β), anti-inflammatory (IL-4r), and regulatory cytokines (IL-5 and IL-10). Preeclamptic women with female fetuses had higher levels of IL-10 in the postpartum period in comparison to those with uncomplicated pregnancies.[29]

fms like tyrosine kinase 1 (sFlt-1)/placental growth factors (PlGF) ratio have shown efficacy in the predictability of the subsequent development of preeclampsia (i.e., angiogenic preeclampsia).[30,31] The potential effect of fetal sex on maternal angiogenic biomarkers during pregnancy has been implicated.[32] In a second analysis, Taylor and colleagues demonstrated women who developed preeclampsia and were carrying male fetal sex had lower sFLT levels compared to those with preeclampsia and carrying a female fetus. However, the authors did not observe such differences among normotensive pregnant women.[33]

Maternal and placental immune balances and during pregnancy could be affected by maternal morbidities and might differ by fetal sex.[34] To assess alterations in proinflammatory placental cytokine expressions in response to maternal asthma, Scott and colleagues examined a representative group of asthmatic women and assessed their placentae.[35] The placentae from asthmatic women with mild asthma had significantly greater cytokine mRNA expressions (TNF-α, IL-1β, IL-6, IL-8, and IL-5) than those from control women. Interestingly, asthma was only associated with increased proinflammatory cytokine expressions in the placentae from female fetuses. The placentae of male fetuses had no change in cytokine expressions regardless of the presence or absence of asthma.[35] The proinflammatory cytokines TNF-α, IL-1β, and IL-6 were inversely associated with female cord blood cortisol; however, this pattern was not observed in placentae from males.[35]

Abnormal placentation could, quantitatively or qualitatively, result in placental dysfunction and development of preeclampsia.[3,13,36] A few studies have investigated the interaction of maternal and prenatal factors with fetal sex affecting the placenta development.[37] Fetal sex-specific effect on differential expression of placental genes regulating cell proliferation, hormone function, and immune tolerance as early as the first trimester has been shown.[38–40] Such fetal sexual dimorphism could affect adaptive responses to alterations in the prenatal environment and differential biological signaling during placenta development.[13,39] [41,42] Fetuses with in-utero exposure to the Dutch famine showed sex-specific adaptations and compensatory expansion of the placental surface that was associated with hypertension in male offspring later in life.[43,44] Maternal obesity could result in sex-specific placental pathologies, with females to be at most risk of chronic villitis and fetal thrombosis, and males with villous edema.[45] Asymmetric growth and expansion of the placental surface area may be sex-specific and subsequently, affect placenta shape and the function of the villous tree resulting in perturbation of placental blood perfusion.[13] More recently, Martin and colleagues identified 582 replicated genes that were differentially methylated in the male term-placentas as compared with the female term-placentas.[41] The majority of the methylated sites were located on the X-chromosome. The sexually dimorphic genes were enriched for proteins involved in immune function, micronutrient transport, transcription, and growth factors.[41]

Polyamines, including spermine, are critical for normal cellular physiology and are involved in several cellular functions including chromatin structure modulation and transcriptional and translational regulation.[46] Gong et al.[47] investigated the fetal-sex specificity of placental polyamine biosynthesis with potential involvement in the pathobiology of human adverse pregnancy outcomes. The authors found that spermine synthase (SMS), a polyamine biosynthesis enzyme, escaped X-chromosome inactivation (XCI) in the placenta. The male primary trophoblast cells demonstrated lower levels of SMS expression and more sensitivity to polyamine depletion. The authors observed that spermine metabolite N1, N12-diacetylspermine (DiAcSpm) was higher in the female placenta and the serum of women pregnant with a female fetus which was associated with an increase in the risk of preeclampsia.[47]

Strength and limitation

While the study has relatively a small sample size compared to the meta-analyses, we used prospectively collected data from a well-designed clinical trial as opposed to several case-control studies included in the meta-analyses. A higher percentage of African American women participated in the VDAART (43.4%) than the general population. This rate of participation might have contributed to the observation in this study in contrast to prior investigations on the relationship between fetal sex and preeclampsia (e.g., an effect among non-Asians). This rate of African American’s participation along with the high rate of participants with vitamin D insufficiency status at the trial enrollment (<30 ng/mL, 78%) might also have contributed to a higher prevalence of preeclampsia in VDAART. Almost 40% of pregnant women participated in the VDAART has a history of asthma. However, there were not any differences in proportions of maternal asthma by maternal race or by preeclampsia status. Nevertheless, the ascertained risks might not reflect the precise estimate in the general population.

CONCLUSION

We demonstrated the maternal race could affect the relationship between fetal sex and risk of preeclampsia development. In this study, African American pregnant women with a male fetus had a higher risk of preeclampsia during their pregnancies. Further studies may shed light on the underlying mechanisms and how sexual dimorphism could affect the pathobiology of preeclampsia. These investigations should demonstrate how tolerance of the fetus by the maternal immune system at the maternal-fetal interface and placental responses in fetal development could differ by fetal sex.