Does interpregnancy BMI change affect the risk of complications in the second pregnancy? Analysis of pooled data from Aberdeen, Finland and Malta

Objective: Weight management interventions during pregnancy have had limited success in reducing the risk of pregnancy complications. Focus has now shifted to pre-pregnancy counselling to optimise body weight before subsequent conception. We aimed to assess the effect of interpregnancy body mass index (BMI) change on the risk of perinatal complications in the second pregnancy. Methods: A cohort study was performed using pooled maternity data from Aberdeen, Finland and Malta. Women with a BMI change of +/- 2 kg/m2 between their first and second pregnancies were compared with those who were BMI stable (remained within +/- 2 kg/m2). Outcomes assessed included pre-eclampsia (PE), intrauterine growth restriction (IUGR), preterm birth, birthweight, and stillbirth in the second pregnancy. We also assessed the effect of unit change in BMI for PE and IUGR. Logistic regression was used to calculate odds ratios with 95% confidence intervals. Results: An increase of ≥ 2 kg/m2 between the first two pregnancies increased the risk of PE (1.66 (1.49 - 1.86)) and high birth weight (> 4000g) (1.06 (1.03 - 1.10)). A reduction of ≥ 2 kg/m2 increased the chance of IUGR (1.15 (1.01 – 1.31)) and preterm birth (1.14 (1.01 – 1.30)), while reducing the risk of instrumental delivery (0.75 (0.68 – 0.85)) and high birth weight (0.93 (0.87- 0.98)). Reducing BMI did not significantly decrease PE risk in women with obesity or those with previous PE. A history of PE or IUGR in the first pregnancy was the strongest predictor of recurrence independent of interpregnancy BMI change (5.75 (5.30 - 6.24) and (7.44 (6.71- 8.25), respectively). Conclusion: Changes in interpregnancy BMI have a modest impact on the risk of high birth weight, PE and IUGR in contrasting directions. However, a prior history of PE and IUGR is the dominant predictor of recurrence at second pregnancy.