• Ellen Aagaard Nohr, Bodil Hammer Bech, Michael John Davies, Morten Frydenberg, Tine Brink Henriksen, and Jorn Olsen.
• Danish Epidemiology Science Centre, Institute of Public Health, University of Aarhus, Aarhus, Denmark. ean@soci.au.dk
• Obstet Gynecol. 2005 Aug 1; 106 (2): 250-9.

ObjectiveTo examine the association between high prepregnancy body mass index and fetal death, allowing for the effects of gestational age, weight gain, and maternal diseases in pregnancy.MethodsPrepregnancy body mass index (BMI) and fetal death were examined in the Danish National Birth Cohort among 54,505 pregnant women who participated in a comprehensive interview during the second trimester. Pregnancy outcomes were obtained from registers and medical records. Cox regression analyses with delayed entry and time-dependent covariates were used to estimate the risk of fetal death.ResultsCompared with normal-weight women (18.5 < or = BMI < 25), the risks of fetal death among obese women (BMI > or = 30), expressed as adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) were as follows: before week 14: 0.8 (0.5-1.4), weeks 14-19: 1.6 (1.0-2.5), weeks 20-27: 1.9 (1.1-3.3), weeks 28-36: 2.1 (1.0-4.4), weeks 37-39: 3.5 (1.9-6.4), and weeks 40+: 4.6 (1.6-13.4). Overweight women (25 < or = BMI < 30) also experienced a higher risk after 28 weeks, and especially after 40 weeks of gestation (HR 2.9, 95% CI 1.1-7.7). Analysis of stillbirth (fetal death at 28+ completed weeks of gestation) indicated that the effects were not due to obesity-related diseases in pregnancy, nor was weight gain associated with stillbirth. The increased risk of stillbirth among overweight and obese women was partly attributable to inadequate placental function (crude odds ratios 2.1, 95% CI 1.0-4.4, and 5.2, 95% CI 2.5-10.9, respectively).ConclusionPrepregnancy obesity was associated with an increasing excess risk of fetal death with advancing gestation, and placental dysfunction may be a possible contributing factor.

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