Title: 607: Maternal obesity and perinatal mortality risk
Abstract: We aimed to quantify the association between maternal body mass index and perinatal mortality rate, looking separately at stillbirths and early neonatal deaths. The cohort consisted of 48, 357 consecutive births during 2006/7 from 6 maternity units in the West Midlands, including 328 stillbirths (from 24.0 weeks) and 240 early neonatal deaths (<7 days). Maternal BMI categories were defined as <20, 20-24.9, 25-29.9, 30-34.9, and 35+. The latter two groups were amalgamated for neonatal deaths because of small numbers. Stillbirth rate increased from 6.2/1000 in the reference BMI range (20-24.9) to 7.6 (25-29.9), 8.5 (30-34.9), and 9.8 (35+). The elevated mortality rate was significant for BMI 30-34.9 (OR 1.4, CI 1.04-2.0) and BMI 35+ (OR 1.6, CI 1.1 – 2.3). Mothers with low BMI (<20) had a significantly reduced rate of stillbirth: 2.8/1000 (OR 0.5, CI 0.3-0.8). In contrast, early neonatal deaths had no such association, with rates ranging from 4.5, 4.6, 5.6, and 5.3/1000 from lowest to highest BMI category. High perinatal mortality associated with obesity is mainly due to an increased rate of stillbirths rather than neonatal deaths. The stillbirth rate of lean mothers is significantly lower than that of mothers with normal BMI.