Prepregnancy Obesity and Fetal Death

TLDR

The study investigates whether high prepregnancy BMI is associated with increased fetal death risk, adjusting for gestational age, weight gain, and maternal diseases. Using the Danish National Birth Cohort, 54,505 women’s prepregnancy BMI and fetal death outcomes were linked to registry data and analyzed with Cox regression incorporating delayed entry and time‑dependent covariates. Obese women had progressively higher hazard ratios for fetal death across gestational weeks, with overweight women also at increased risk after 28 weeks; stillbirth risk was not explained by obesity‑related diseases or weight gain but was partly linked to placental dysfunction, indicating that prepregnancy obesity elevates fetal death risk as pregnancy advances.

Abstract

In Brief Objective: To 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. Methods: Prepregnancy 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. Results: Compared with normal-weight women (18.5 ≤ BMI < 25), the risks of fetal death among obese women (BMI ≥ 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 ≤ 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). Conclusion: Prepregnancy obesity was associated with an increasing excess risk of fetal death with advancing gestation, and placental dysfunction may be a possible contributing factor. Level of Evidence: II-2 Prepregnancy obesity is associated with an increasing excess risk of fetal death with advancing gestation.