Maternal and fetal risk factors for stillbirth: population based study

Abstract

Objective: To assess the main risk factors associated with stillbirth in a multiethnic English maternity population.

Design: Cohort study.

Setting: National Health Service region in England.

Population: 92,218 normally formed singletons including 389 stillbirths from 24 weeks of gestation, delivered during 2009-11.

Main outcome measure: Risk of stillbirth.

Results: Multivariable analysis identified a significant risk of stillbirth for parity (para 0 and para ≥ 3), ethnicity (African, African-Caribbean, Indian, and Pakistani), maternal obesity (body mass index ≥ 30), smoking, pre-existing diabetes, and history of mental health problems, antepartum haemorrhage, and fetal growth restriction (birth weight below 10th customised birthweight centile). As potentially modifiable risk factors, maternal obesity, smoking in pregnancy, and fetal growth restriction together accounted for 56.1% of the stillbirths. Presence of fetal growth restriction constituted the highest risk, and this applied to pregnancies where mothers did not smoke (adjusted relative risk 7.8, 95% confidence interval 6.6 to 10.9), did smoke (5.7, 3.6 to 10.9), and were exposed to passive smoke only (10.0, 6.6 to 15.8). Fetal growth restriction also had the largest population attributable risk for stillbirth and was fivefold greater if it was not detected antenatally than when it was (32.0% v 6.2%). In total, 195 of the 389 stillbirths in this cohort had fetal growth restriction, but in 160 (82%) it had not been detected antenatally. Antenatal recognition of fetal growth restriction resulted in delivery 10 days earlier than when it was not detected: median 270 (interquartile range 261-279) days v 280 (interquartile range 273-287) days. The overall stillbirth rate (per 1000 births) was 4.2, but only 2.4 in pregnancies without fetal growth restriction, increasing to 9.7 with antenatally detected fetal growth restriction and 19.8 when it was not detected.

Conclusion: Most normally formed singleton stillbirths are potentially avoidable. The single largest risk factor is unrecognised fetal growth restriction, and preventive strategies need to focus on improving antenatal detection.

Fig 1 Stillbirth rates in relation to fetal growth restriction and whether it was detected antenatally

Fig 2 Stillbirths and live births with and without fetal growth restriction: cumulative percentage graph of gestational age at delivery