[Effects of pre-pregnancy body mass index on pregnancy outcomes]

To explore the effects of pre-pregnancy body mass index (BMI) upon adverse pregnancy outcomes.

We selected a population-based cohort of 48 867 nulliparous women in mainland China with singleton and full-term deliveries in 2011. The cohort was categorized in accordance with pre-pregnancy BMI as follows: underweight <18.5; normal weight = 18.5-23.9; overweight = 24-27.9; obesity ≥ 28. Logistic regression was used to estimate the association between BMI and adverse maternal, peripartum and perinatal outcomes with normal weight as a reference range.

(1) Overweight and obese women were more likely to have hypertensive disorders with odds ratios of 2.29 and 6.02, gestational diabetes mellitus 2.27, 4.99; (2)the odds ratios for fetal macrosomia increased among women with higher BMI as follows: 0.59, 1.99 and 3.15, whereas only lean women had significantly increased risk of delivering babies with low birth weight (LBW) 1.62; (3)increased BMI was associated with reduced rates of assisted vaginal delivery and increased rates of caesarean section.

As an independent risk factor for adverse maternal and fetal outcomes, pre-pregnancy obesity should be managed properly.