Partner change, birth interval and risk of pre-eclampsia: a paradoxical triangle

Assessing the effects of duration of birth interval on adverse pregnancy outcomes in sub-Saharan Africa: a propensity score-matched analysis

OBJECTIVES

Unlike high-income countries, sub-Saharan African countries have the highest burden of adverse pregnancy outcomes such as abortion, stillbirth, low birth weight and preterm births. The WHO set optimal birth spacing as a key strategy to improve pregnancy outcomes. Estimating the impact of short and long birth intervals on adverse pregnancy outcomes based on an observational study like the Demographic and Health Survey (DHS) is prone to selection bias. Therefore, we used the propensity score-matched (PSM) analysis to estimate the actual impact of short and long birth intervals on adverse pregnancy outcomes.

DESIGN

A community-based cross-sectional study was conducted based on the DHS data.

SETTING

We used the recent DHS data of 36 sub-Saharan African countries.

PARTICIPANTS

A total of 302 580 pregnant women for stillbirth and abortion, 153 431 for birth weight and 115 556 births for preterm births were considered.

PRIMARY OUTCOME MEASURES

To estimate the impact of duration of birth interval (short/long) on adverse pregnancy outcomes, we used PSM analysis with logit model using psmatch2 ate STATA command to find average treatment effect on the population (ATE), treated and untreated. The quality of matching was assessed statistically and graphically. Sensitivity analysis was conducted to test the robustness of the PSM estimates using the Mantel-Haenszel test statistic.

RESULTS

The prevalence of short and long birth intervals in sub-Saharan Africa was 46.85% and 13.61%, respectively. The prevalence rates of abortion, stillbirth, low birth weight, macrosomia, and preterm births were 6.11%, 0.84%, 9.63%, 9.04%, and 4.87%, respectively. In the PSM analysis, the differences in ATE of short birth intervals on abortion, stillbirth, low birth weight, and preterm births were 0.5%, 0.1%, 0.2%, and 0.4%, respectively, and -2.6% for macrosomia. The difference in ATE among the treated group was 1%, 1%, and 1.1% increased risk of abortion, low birth weight, and preterm births, respectively, while there was no difference in risk of stillbirth between the treated and control groups. The ATEs of long birth intervals on abortion, stillbirth, low birth weight, macrosomia and preterm births were 1.3%, 0.4%, 1.0%, 3.4%, and 0.2%, respectively. The ATE on the treated group had 0.9%, 0.4%, 2.4%, 2.8%, and 0.2% increased risk of abortion, stillbirth, low birth weight, macrosomia, and preterm births, respectively. The estimates were insensitive to hidden bias and had a good quality of matching.

CONCLUSION

Short and long birth intervals had a significant positive impact on stillbirth, abortion, low birth weight, macrosomia and preterm births after matching treated and control groups by observed variables. These findings highlighted maternal and newborn healthcare programmes and policies to empower reproductive-aged women to exercise optimal birth spacing to reduce the incidence of stillbirth, abortion, low birth weight, macrosomia and preterm births.

Comparison of clinical features and pregnancy outcomes in early- and late-onset preeclampsia with HELLP syndrome: a 10-year retrospective study from a tertiary hospital and referral center in China

Background

Early-onset preeclampsia (EO-PE) and late-onset preeclampsia (LO-PE) are different subtypes of preeclampsia. We conducted this study to analyze the similarities and differences in the clinical features and pregnancy outcomes in EO- and LO-PE with HELLP syndrome.

Methods

This was a retrospective study in a tertiary hospital. Eighty-three parturients with HELLP syndrome were allocated into two groups based on the timing of preeclampsia onset: EO-PE with HELLP (n = 47) and LO-PE with HELLP (n = 36).

Results

In total, 31.9% and 63.9% of women in the EO-PE with HELLP and LO-PE with HELLP groups, respectively, were asymptomatic at diagnosis (P = 0.004, OR = 0.265 (0.106–0.662)). Headache or visual symptoms were more frequent in the EO-PE group than in the LO-PE group (48.9% vs. 25%, P = 0.026, OR = 0.348 (0.135–0.896)). Women in the EO-PE with HELLP group had higher SBP and DBP than those in the LO-PE with HELLP group. Laboratory tests, including platelets, liver function, and hemolysis, which are the main indicators for the diagnosis of HELLP syndrome, showed almost no significant differences between the two groups, with kidney function being the only difference observed. Women in the EO-PE with HELLP group had higher Scr than those in the LO-PE with HELLP group. The degree of proteinuria was higher in the EO-PE group than in the LO-PE with HELLP group. The incidence of severe maternal complications was significantly higher in the EO-PE group than in the LO-PE with HELLP group (25.5% vs. 5.6%, P = 0.016, OR = 0.172 (0.036–0.824)). In total, 57.4% and 8.3% of neonates in the EO-PE and LO-PE with HELLP groups were admitted to the NICU, and the difference was statistically significant, even after adjustment for the delivery week (P = 0.009, OR = 0.830 (0.729–0.944)). Postpartum HELLP syndrome was more common in the LO-PE group than in the EO-PE group (30.6% vs. 4.3%, P = 0.001, OR = 9.9 (2.031–48.256)).

Conclusions

Compared with LO-PE with HELLP patients, EO-PE with HELLP patients have more obvious kidney damage, higher blood pressure and a higher risk of adverse maternal and neonatal outcomes. Patients with LO-PE need to be alerted to the occurrence of HELLP syndrome after delivery.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-022-04466-9.

Interpregnancy interval and hypertensive disorders of pregnancy: A population-based cohort study

BACKGROUND

Despite extensive research on risk factors and mechanisms, the extent to which interpregnancy interval (IPI) affects hypertensive disorders of pregnancy in high-income countries remains unclear.

OBJECTIVES

To examine the association between IPI and hypertensive disorders of pregnancy in a high-income country setting using both within-mother and between-mother comparisons.

METHODS

A retrospective population-based cohort study was conducted among 103 909 women who delivered three or more consecutive singleton births (n = 358 046) between 1980 and 2015 in Western Australia. We used conditional Poisson regression with robust variance, matching intervals of the same mother and adjusted for factors that vary within-mother across pregnancies, to investigate the association between IPI categories (reference 18-23 months), and the risk of hypertensive disorders of pregnancy. For comparison with previous studies, we also applied unmatched Poisson regression (between-mother analysis).

RESULTS

The incidence of preeclampsia and gestational hypertension during the study period was 4%, and 2%, respectively. For the between-mother comparison, mothers with intervals of 6-11 months had lower risk of preeclampsia with adjusted relative risk (RR) 0.92 (95% confidence interval [CI] 0.85, 0.98) compared to reference category of 18-23 months. With the within-mother matched design, we estimated a larger effect of long IPI on risk of preeclampsia (RR 1.29, 95% CI 1.18, 1.42 for 60-119 months; and RR 1.30, 95% CI 1.10, 1.53 for intervals ≥120 months) compared to 18-23 months. Short IPIs were not associated with hypertensive disorders of pregnancy.

CONCLUSIONS

In our cohort, longer IPIs were associated with increased risk of preeclampsia. However, there was insufficient evidence to suggest that short IPIs (<6 months) increase the risks of hypertensive disorders of pregnancy.

In vitro fertilization is associated with the onset and progression of preeclampsia

OBJECTIVE

We aimed to estimate the risk of preeclampsia (PE) associated with in vitro fertilization (IVF) and potential predisposing factors responsible for the observed association.

METHODS

This retrospective cohort study included 114485 pregnant women who delivered at the Nanjing Maternity and Child Health Care Hospital between 2013 and 2018. Of the 114485 women, 4601 (4%) conceived through IVF (IVF group) and 109884 (96%) conceived spontaneously (SC group). We performed logistic regression analysis to evaluate the risk of PE following IVF compared to spontaneous conception (SC). Then, we used propensity score matching analysis to compare the clinical characteristics and pregnancy outcomes between IVF patients with and without PE.

RESULT

There were 1339 PE cases in the total study population, with a significantly higher incidence of PE in IVF relative to spontaneous pregnancies (6.1% vs. 1.0%, p < 0.01). Severe PE was more prevalent in singleton IVF-PE group than in singleton SC-PE group (40% vs. 24.1%, p = 0.025). Placenta accreta was more common in singleton preeclamptic patients with IVF than without IVF (12.5vs.2.6%, p = 0.003). Placental hypoxia was more prevalent in twin IVF pregnancies with PE than without PE (6% vs. 12.2%, p = 0.045). Moreover, the IVF-PE group showed more frequent first-trimester bleeding (31.6% vs. 10.5%, p = 0.024) compared to the control group.

CONCLUSION

IVF is associated with the onset and progression of PE. Defective placentation and placental insufficiency may predispose IVF patients to PE and may manifest as first-trimester bleeding.

Comparison of maternal serum lipoproteins in normal pregnancy and primiparous patients with eclampsia

Objective:

To evaluate changes in serum lipoproteins in primiparous women with eclampsia and compare it with pregnant women having normal blood pressure.

Methods:

This cross sectional study was conducted on 65 primiparous eclamptic patients and 21 normotensive pregnant women in the tertiary care hospitals of Peshawar. History of each woman was recorded on a questionnaire. Blood pressure was measured using standard methods. About 5 ml of venous blood was drawn for the analysis of lipoproteins. The data was analyzed using computer software package SPSS version 10. The P value <0.05 was considered statistically significant.

Results:

Mean age of hypertensive cases was 23.2 ± 0.52 years while that for controls was 23.9 ± 1.16 years. Significant differences were found in serum lipoproteins. Women having eclampsia had 28.8%, 29.5%, 31.1%, 32.9% and 65.3% higher, low density lipoprotein-cholesterol (LDLC), triglycerides (TG), total cholesterol (TC):high density lipoprotein-cholesterol (HDLC) ratio, LDLC: HDLC ratio and TG: HDLC ratio respectively as compared to the control group. The HDLC concentrations, HDLC: VLDLC ratio and apolipoprotein-A1 level were 26.9%, 56.6% and 27.9% respectively, lower in the patient group as compared to the controls.

Conclusion:

This study suggests that evaluation of lipoprotein concentrations during antenatal period can be helpful in the early detection and prevention of developing eclampsia.

Inter-pregnancy interval and risk of recurrent pre-eclampsia: systematic review and meta-analysis

BACKGROUND

Women with a history of pre-eclampsia have a higher risk of developing pre-eclampsia in subsequent pregnancies. However, the role of the inter-pregnancy interval on this association is unclear.

OBJECTIVE

To explore the effect of inter-pregnancy interval on the risk of recurrent pre-eclampsia or eclampia.

SEARCH STRATEGY

MEDLINE, EMBASE and LILACS were searched (inception to July 2015).

SELECTION CRITERIA

Cohort studies assessing the risk of recurrent pre-eclampsia in the immediate subsequent pregnancy according to different birth intervals.

DATA COLLECTION AND ANALYSIS

Two reviewers independently performed screening, data extraction, methodological and quality assessment. Meta-analysis of adjusted odds ratios (aOR) with 95 % confidence intervals (CI) was used to measure the association between various interval lengths and recurrent pre-eclampsia or eclampsia.

MAIN RESULTS

We identified 1769 articles and finally included four studies with a total of 77,561 women. The meta-analysis of two studies showed that compared to inter-pregnancy intervals of 2-4 years, the aOR for recurrent pre-eclampsia was 1.01 [95 % CI 0.95 to 1.07, I(2) 0 %] with intervals of less than 2 years and 1.10 [95 % CI 1.02 to 1.19, I(2) 0 %] with intervals longer than 4 years.

CONCLUSION

Compared to inter-pregnancy intervals of 2 to 4 years, shorter intervals are not associated with an increased risk of recurrent pre-eclampsia but longer intervals appear to increase the risk. The results of this review should be interpreted with caution as included studies are observational and thus subject to possible confounding factors.

An analysis of the differences between early and late preeclampsia with severe hypertension

Preeclampsia is clinically divided into early onset and late onset preeclampsia based on the gestational age at delivery. Although the diagnostic criteria are the same in each subgroup of preeclampsia, it has been suggested that the maternal and perinatal mortalities of early onset and late onset preeclampsia are different. However, studies that compare clinical parameters or laboratory biomarkers between early onset and late onset preeclampsia are limited. Data on 177 women with early or late preeclampsia with severe hypertension were collected from a University Teaching Hospital from January 2010 to January 2011 and analysed. Data included all the clinical parameters and laboratory biomarkers of liver and renal function. 63 women and 114 women were diagnosed with early and late preeclampsia with severe hypertension, respectively. There was no difference in the maternal age and the incidence of clinical symptoms including edema, vision disturbance, severe headache and stillbirth between two groups. There was a decrease in alkaline phosphatase levels in early preeclampsia with severe hypertension but other markers of liver function were not altered. However, renal function including blood urea nitrogen, creatinine and uric acid were significantly higher in early preeclampsia with severe hypertension. Umbilical artery systolic velocity/diastolic velocity ratio was significantly higher in early preeclampsia with severe hypertension. Our data demonstrates that the laboratory biomarkers of renal function differ between early and late preeclampsia with severe hypertension. The severity of renal dysfunction correlated with the time of delivery in preeclampsia with severe hypertension.

Is ethnicity a risk factor for developing preeclampsia? An analysis of the prevalence of preeclampsia in China

Preeclampsia is a major complication of pregnancy. Risk factors for preeclampsia include population and regional ethnicity. Chinese women living outside the Chinese mainland have a lower prevalence of preeclampsia than resident Caucasians. We performed a retrospective study to identify potential factors that may be associated with developing preeclampsia in China. A total of 67,746 pregnant women were included in this study from 2002 to 2011. Data included maternal age, maternal body mass index (BMI), age at marriage, parity, gestation and blood pressure at diagnosis, proteinuria, and birth weight. In the study period, 1301 (1.92%) nulliparous women developed preeclampsia. The prevalence of mild or severe preeclampsia was 1.42% or 0.49%, respectively. The average BMI was 21.61 kg m(-2). On the basis of the WHO BMI classification, 78.8% of women were of normal BMI, 18.3% were overweight and 2.9% were obese. A total of 37.8% of preeclamptic women had lived with the same partner for less than 1 year, which was significantly higher than those healthy pregnant women who did not develop preeclampsia (24.2%). The prevalence of preeclampsia in China is low compared with Caucasians, and the contribution to this lower prevalence may be dependent on BMI or lifestyle including period of cohabitation with the partner. Our data suggest that Chinese ethnicity may be a factor responsible for the low risk of developing preeclampsia in the populations studied.

Change in paternity and select perinatal outcomes: causal or confounded?

Select social, behavioural and maternal characteristics were evaluated to determine if they were confounding factors in the association between paternity change and pre-eclampsia, small for gestational age (SGA) and pre-term delivery, in a sample of 1,409 women. Multivariate logistic regression analysis was used to determine if any of these risk factors modified the association between changing paternity and the selected perinatal outcomes. Results of the analysis showed that women who changed partners were more likely to possess potentially confounding risk factors compared with those who had not. Paternity change was 2.75 times more likely to be associated with the development of pre-eclampsia (95% CI 1.33; 5.68) and 2.25 times more likely to be associated with an SGA infant on weight (95% CI 1.13; 4.47), after adjusting for selected risk factors. Paternity change remains a significant risk factor for pre-eclampsia and SGA in the presence of select risk factors.

Regulatory T cells in preeclampsia: some answers, more questions?

This Commentary highlights the article by Hsu et al (in this issue) reporting an enrichment in induced regulatory T cells (iTregs) in normal pregnancy but not in preeclampsia, implicating iTreg defect as central to the pathogenesis of preeclampsia.

Group B streptococcal colonization and the risk of pre-eclampsia

To determine if there was an association between recto-vaginal group B streptococcus (GBS) colonization and pre-eclampsia, two cross-sectional studies were conducted using statewide hospital databases. The first study analysed data from the state of Florida, USA, and included 190 645 women who were discharged in 2001. This dataset was used to generate the hypothesis that GBS colonization is associated with pre-eclampsia. The second study tested the GBS hypothesis using the records of 577 153 women who delivered in 2004 or 2005 in Texas, USA. Adjusted odds ratios (aOR) for the outcome of pre-eclampsia comparing GBS-positive to GBS-negative women were calculated using logistic regression. The aOR for the association between GBS carriage and pre-eclampsia was 0·71 [95% confidence interval (CI) 0·65–0·77] in the Florida dataset. In the Texas dataset, the overall prevalence of GBS carriage was 14·1% while the overall prevalence of pre-eclampsia was 4·0%. GBS carriers were 31% less likely than non-carriers to have pre-eclampsia (aOR 0·69, 95% CI 0·66–0·72) in Texas. In two large statewide analyses, GBS carriage was inversely associated with pre-eclampsia. A sensitivity analysis revealed that misclassification of GBS status is not a likely explanation of our findings.

FOLATE METABOLISM AND PREECLAMPSIA

Preeclampsia (PE) is a multisystem disorder of human pregnancy, affecting about 6% of all pregnancies worldwide, and is one of the leading causes of maternal and infant morbidity and mortality. Despite decades of research into the pathogenesis of this complex disease, the underlying mechanisms remain unclear. As a result, the options for prevention and management of PE are limited. In recent years, there has been a growing body of evidence suggesting that folate deficiency is associated with PE, and folic acid supplementation may reduce the risk of developing PE in certain populations. Folate contributes to cell division and growth, and folate metabolism is involved in a large number of physiological and pathophysiological processes in human development. Sufficient supply of folate is therefore particularly important during pregnancy. Nevertheless, the exact mechanisms of folic acid deficiency increasing the risk of developing PE are still unclear. This article reviews what is understood about the aetiology of PE and the relationship between folate metabolism and PE so as to enhance further discussions on the subject.

Blood lead, calcium, and phosphorus in women with preeclampsia in Edo State, Nigeria

The authors investigated the effect of blood lead (BPb) and its relationship with calcium and phosphorus in the development of preeclampsia in Nigeria. Blood samples were collected from 59 preclamptics, 150 normal pregnant, and 122 nonpregnant women. Blood lead and serum Ca and P were determined. Blood lead was significantly higher (p < .001), whereas serum Ca and P were significantly lower (p < .001) in preclamptics than in normal pregnant women (60.2 ± 12.8 vs 26.3 ± 8.0 μg/dL for Pb, 1.39 ± 0.33 vs 2.03 ± 0.22 mmol/L for Ca, and 0.76 ± 0.10 vs 0.99 ± 0.13 mmol/L for P, respectively). There was significant increase (p < .05) in BPb and decreases (p < .01) in serum Ca and P in pregnant women than in nonpregnant women (35.7 ± 18.0 vs 13.1 ± 6.4 μg/dL for Pb, 1.85 ± 0.33 vs 2.33 ± 0.20 mmol/L for Ca, and 0.93 ± 0.38 vs 1.24 ± 0.26 mmol/L for P). Also, BPb was negatively correlated with serum Ca and, P, and positively correlated with systolic and diastolic blood pressures in pregnancy (r = -.804 for Ca, r = -.728 for P, r = .908 for SBP, and r = .842 for DBP) and preeclampsia (p < .01). It appears that increase in blood lead, which parallels decreases in serum calcium and phosphorus, may be related to the development and progression of preeclampsia in this environment.

The paternal role in pre-eclampsia and giving birth to a small for gestational age infant; a population-based cohort study

OBJECTIVE

To estimate the effect of partner change on risks of pre-eclampsia and giving birth to a small for gestational age infant.

DESIGN

Prospective population study.

SETTING

Sweden.

PARTICIPANTS

Women with their first and second successive singleton births in Sweden between 1990 and 2006 without pregestational diabetes and/or hypertension (n=446 459).

OUTCOME MEASURES

Preterm (<37 weeks) and term (≥37 weeks) pre-eclampsia, and giving birth to a small for gestational age (SGA) infant. Risks were adjusted for interpregnancy interval, maternal age, body mass index, height and smoking habits in second pregnancy, years of involuntary childlessness before second pregnancy, mother's country of birth, years of formal education and year of birth. Further, when we calculated risks of SGA we restricted the study population to women with non-pre-eclamptic pregnancies.

RESULTS

In women who had a preterm pre-eclampsia in first pregnancy, partner change was associated with a strong protective effect for preterm pre-eclampsia recurrence (OR 0.24; 95% CI 0.07 to 0.88). Similarly, partner change was also associated with a protective effect of recurrence of SGA birth (OR 0.75; 95% CI 0.67 to 0.84). In contrast, among women without SGA in first birth, partner change was associated with an increased risk of SGA in second pregnancy. Risks of term pre-eclampsia were not affected by partner change.

CONCLUSIONS

There is a paternal effect on risks of preterm pre-eclampsia and giving birth to an SGA infant.

Preterm delivery and risk of subsequent cardiovascular morbidity and type-II diabetes in the mother

OBJECTIVE

Preterm delivery has been shown to be associated with subsequent maternal cardiovascular morbidity. However, the impact of the severity and recurrence of preterm delivery on the risk of specific cardiovascular events and the metabolic syndrome in the mother, have not been investigated.

DESIGN

National registry-based retrospective cohort study.

SETTING

Women delivering in Denmark from 1978 to 2007.

POPULATION

Women with a first singleton delivery (n = 782 287), and with a first and second singleton delivery (n = 536 419).

METHODS

Cox proportional hazard models, with the gestational age stratified into four groups as primary exposure. We made adjustments for maternal age, year of delivery, hypertensive pregnancy disorders, fetal growth deviation, placental abruption and stillbirth.

MAIN OUTCOME MEASURES

Subsequent maternal hypertension, ischaemic heart diseases, thromboembolism and type-II diabetes.

RESULTS

After a first delivery at 32-36 completed weeks of gestation, the adjusted risk of subsequent type-II diabetes increased 1.89-fold (1.69-2.10) and the risk of thromboembolism increased 1.42-fold (1.24-1.62). Women having a preterm delivery in the first pregnancy and a term delivery in the second had a 1.58-fold (1.34-1.86) increased risk of type-II diabetes and a 1.18-fold (0.96-1.44) increased risk of thromboembolism. Women having two preterm deliveries had a 2.30-fold (1.71-3.10) increased risk of type-II diabetes and a 1.80-fold (1.29-2.50) increased risk of thromboembolism.

CONCLUSIONS

Preterm delivery is independent of other pregnancy complications associated with subsequent maternal overt type-II diabetes and thromboembolism. The recurrence of preterm delivery will augment these risks.

Effects of interpregnancy interval on blood pressure in consecutive pregnancies

The lower risk of preeclampsia observed in parous women has prompted a hypothesis that cardiovascular adaptation from a first pregnancy has ongoing benefits which contribute to a reduced risk of preeclampsia in the second pregnancy. However, how the interpregnancy interval affects mean arterial pressure (MAP) as an indicator of cardiovascular adaptation in subsequent pregnancies has not been well studied. The authors examined the effect of interpregnancy interval on MAP in consecutive pregnancies using data from the Collaborative Perinatal Project (1959-1965) and a semiparametric random-effects regression model. Prenatal MAP measurements were available for 533 women with both first and second births. MAP was lower in the second pregnancy (by approximately 2 mmHg) for very short interpregnancy intervals. However, this difference diminished when the interval increased, and it totally disappeared for intervals longer than 2 years. The authors conclude that although MAP is lower in the second pregnancy than in the first pregnancy, the effect persists for only a short time. It is therefore unlikely that mechanisms involving MAP as an indicator of cardiovascular adaptation contribute appreciably to the reduced risk of preeclampsia in subsequent pregnancies. However, it does not rule out the possibility that other mechanisms of cardiovascular adaptation persist longer.

Partner change and perinatal outcomes: a systematic review

Epidemiological studies suggest that partner change may affect perinatal outcomes in subsequent pregnancies. We conducted a systematic review on the association between paternity change and perinatal outcomes. We searched the literature in MEDLINE using keywords 'paternity', 'partner', 'pre-eclampsia', 'preterm birth', 'low birth weight', and 'birth defects' from 1966 to 2005. We identified 19 studies that examined the association between partner change and specific perinatal outcomes: 12 on pre-eclampsia or hypertension in pregnancy, three on birth defects, three on preterm birth, and two on low birthweight. Partner change was consistently associated with an increased risk of pre-eclampsia or hypertension in pregnancy in 11 of 12 studies (the unadjusted relative risk [RR] ranging from 1.2 to 8.3). However, after controlling for birth interval as a confounder in multivariate analysis, two studies using the same birth registry data showed a modestly reduced risk in relation to partner change (RR=0.84 and 0.73, respectively), while two studies found a slightly increased risk (both RR=1.3). Retrospective cohort studies presented inconsistent findings on the association between partner change and risk of preterm birth and low birthweight. Finally, three population-based cohort studies demonstrated that partner change significantly reduced the recurrence of the same or similar birth defects in subsequent births (RRs ranging from 0.1 to 0.76). We conclude that partner change reduces the risk of recurrent same birth defects. However, epidemiological evidence on the effect of partner change on pre-eclampsia, preterm birth and low birthweight is inconclusive. Whether birth interval should be controlled for in the association between partner change and pre-eclampsia warrants caution.