O6. Association between fetal congenital heart defects and maternal risk of hypertensive disorders of pregnancy in concurrent and subsequent pregnancies

Introduction Pregnant women carrying fetuses with heart defects and women with hypertensive disorders of pregnancy (HDP) both often exhibit angiogenic imbalances, suggesting that the same underlying processes may play a role in the etiology of heart defects and the pathology associated with HDP. Objectives To determine whether fetal heart defects are associated with an increased risk of maternal HDP, and whether the mechanisms driving the association are primarily maternal or fetal. Methods Using Danish national registers, we constructed a cohort comprising all singleton pregnancies without chromosomal abnormalities continuing to at least 20 completed weeks gestation in Denmark, 1977–2011. We then identified both pregnancies complicated by offspring congenital heart defects and those complicated by HDP (severe preeclampsia [PE]/eclampsia, moderate PE, gestational hypertension [GH]). Using polytomous logistic regression, we estimated odds ratios (ORs) for the association between carrying a fetus with a congenital heart defect and maternal risk of an HDP in the second half of pregnancy, overall and for specific heart defects. We also estimated ORs for the association between (1) an HDP in a previous pregnancy and the risk of carrying a child with a heart defect in subsequent pregnancies, and (2) fetal congenital heart defects in a previous pregnancy and the risk of HDP in subsequent pregnancies. Results Carrying a child with a heart defect was associated with a 3-fold increase in the risk of severe PE later in pregnancy (OR 3.02, 95% confidence interval [CI] 2.71–3.37) and a modest increase in the risk of moderate PE (OR 1.29, 95% CI 1.18–1.41), but not with the risk of GH (OR 1.08, 95% CI 0.93–1.25). These associations did not appear to depend on the type of offspring heart defect. Having a child with a heart defect in a previous pregnancy was also associated with PE (severe PE: OR 1.57, 95% CI 1.24–1.97; moderate PE: OR 1.32, 95% CI 1.16–1.51) but not with GH (OR 1.00, 95% CI 0.82–1.22) in subsequent pregnancies. Similarly, a history of PE in a previous pregnancy, but not of GH alone, was associated with an increased risk of offspring heart defects in later pregnancies (severe PE: OR 1.46, 95% CI 1.21–1.77; moderate PE: OR 1.13, 95% CI 1.01–1.27; GH: OR 1.12, 95% CI 0.91–1.37). Conclusion Our findings suggest that the same pathophysiological mechanisms may be involved in both congenital heart defects and severe PE (but are less important in less severe forms of HDP), and that these processes are most likely maternal, rather than fetal.