Background Early pregnancy obesity (body mass index (BMI) >30 kg/m²) carries significant health implications. This study matched data from hospitals with a population-based register of fetal and infant deaths to investigate the association between early pregnancy obesity and risk of fetal and infant death.

Methods Data on singleton pregnancies delivered between 2003 and 2005 at five maternity units in Northern England were linked with data from the Northern Perinatal Mortality Survey. Cases associated with pregestational diabetes or congenital anomalies were excluded. Logistic regression models were used to determine the adjusted OR (AOR) of a fetal or infant death among obese women, compared to those of recommended BMI (18.5–24.9 kg/m²).

Results 40 932 singleton pregnancies were identified during the study period, including 75 ending in spontaneous abortion (gestation 20–24 weeks), 65 in termination of pregnancy for fetal anomaly (gestation 20+ weeks) and 200 in stillbirth (gestation 24+ weeks). There were 92 neonatal deaths and 55 postneonatal deaths. Compared to women of recommended BMI, obese women were at significantly greater odds of spontaneous abortion (AOR=3.27 (95% CI 1.43 to 7.44), p=0.005), stillbirth (2.77 (1.86 to 4.13), p<0.001) and neonatal death (2.57 (1.13 to 5.88), p=0.03). There was weak evidence of increased odds of postneonatal death (2.27 (0.89 to 5.80), p=0.09). Except for higher rates of pre-eclamptic toxaemia among stillbirths, no cause of death explained the increased fetal and neonatal death rate among obese pregnant women.

Conclusion This study found significantly increased odds of fetal and neonatal death among obese pregnant women. Women should be aware of these risks and ideally optimise their weight before pregnancy.