Risk of Adverse Pregnancy Outcomes by Pre-pregnancy Body Mass Index Among Italian Population: a Retrospective Population-based Cohort Study on 27,807 Deliveries

Purpose: To estimate the impact of increasing pre-pregnancy Body Mass Index (BMI) on the risk of adverse maternal and perinatal outcomes, in patients who delivered in an Italian tertiary care Obstetric department.

Methods: Data, related to women who delivered at Sant'Anna Hospital, Turin, between 2011 and 2015, were collected retrospectively from the hospital database. According to BMI, women were considered as normal weight, overweight, and class 1, 2 and 3 obese (WHO criteria). Logistic regression analysis studied the impact of BMI on maternal and neonatal outcomes, adjusting results for maternal age and parity. Adjusted absolute risks of each outcome were reported according to incremental values in pre-pregnancy BMI.

Results: A total of 27,807 women were included. 75.8% of pregnancies occurred among normal-weight women, whereas 16.7% were overweight, and 7.5% obese women (5.4% class 1, 1.7% class 2 and 0.4% class 3). A 10% decrease in pre-pregnancy BMI was associated with a reduction of at least 15% of Gestational diabetes mellitus (GDM), preeclampsia, maternal admission to intensive care unit (ICU), macrosomia, APGAR 5' < 6 and neonatal admission to ICU. GDM and preeclampsia resulted in the highest reduction being almost 30%. Larger differences in BMI (20-25%) corresponded to at least a 10% in reduction of risk of preterm and very preterm delivery and emergency cesarean section. Differences in maternal pre-pregnancy BMI had no impact on the frequency of shoulder dystocia and stillbirth.

Conclusions: This study offers a quantitative estimation of negative impact of pre-pregnancy obesity on the most common pregnancy and perinatal complications.