The risk of complications in second pregnancy by maternal BMI: The role of first‐pregnancy complications, pregestational diabetes and chronic hypertension

Introduction Maternal obesity is associated with an increased risk of several pregnancy complications. In the second pregnancy, previous pregnancy and other medical history provide additional information about individual morbidity risk. In this study, we assess the risk of pregnancy complications in the second pregnancy by maternal body mass index (BMI) and evaluate how first‐pregnancy complications and preexisting conditions modify these associations. Material and methods We have used nationwide data on all women (n = 48 963) experiencing their first and second pregnancy between 2006 and 2013 in Finland. The associations between the full scale of maternal BMI and pregnancy complications (gestational diabetes, gestational hypertension and preeclampsia) were analyzed using logistic regression and restricted cubic spline regression models and interactions between BMI and first‐pregnancy complications, pregestational diabetes or chronic hypertension were tested. Results The risk of pregnancy complications increased with adiposity. Unadjusted probability of second‐pregnancy gestational diabetes with BMI of 25 kg/m2 was 56% and 8.4% among women with and without first‐pregnancy gestational diabetes, respectively. The corresponding figures with BMI of 30 kg/m2 were 64% and 17%. Adjusted odds ratio (OR) (95% CI) for second‐pregnancy gestational diabetes with BMI of 25 kg/m2 was 45 (34‐59) and 3.3 (2.6‐4.0) among women with and without first‐pregnancy gestational diabetes, respectively, when compared with women with BMI of 20 kg/m2 and no first‐pregnancy gestational diabetes. Adjusted OR (95% CI) for second‐pregnancy gestational hypertension among women with BMI of 25 kg/m2 was 42 (26‐66) and 2.3 (1.4‐3.8) among women with and without first‐pregnancy hypertensive disorder, respectively, when compared with women with BMI of 20 kg/m2 and no first‐pregnancy hypertensive disorder. The risk of preeclampsia increased with adiposity independent of first‐pregnancy complications. Pregestational diabetes or chronic hypertension did not modify the association between adiposity and any of the second‐pregnancy complications. Conclusions As maternal BMI increases, the risk of complications increases in the second pregnancy. The risk of gestational diabetes and hypertension is, however, highest among women with complications in the first pregnancy.