Mandy Williams

Maternal and fetal risk factors for stillbirth: population based study

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.

W5.2 The effect of smoking during pregnancy on incidence of hypertensive diseases, prematurity and intrauterine growth restriction

Objective: We wanted to evaluate the pregnancy related factors associated with stillbirth (SB), with specific emphasis on the role of fetal growth restriction and hypertensive diseases in pregnancy. Method: The cohort consisted of 49,384 consecutive pregnancies delivered between 1990 and 2008 in St Louis, USA. Major congenital anomalies and cases with incomplete data were excluded. For SB (n=252), a standard 2 days was deducted from gestational age at birth to adjust for the average fetal death-to-delivery interval. Variables for logistic regression included maternal characteristics (parity, ethnicity, high (<20) and low (≥30) body mass index (BMI), smoking, preterm labour (PTL), preterm premature rupture of membranes (PROM), abruption, gestational diabetes, hypertensive disease in pregnancy (preeclampsia, PE, and gestational hypertension, GH), and fetal growth restriction (FGR). FGR was defined as birthweight <10th customised centile, adjusted for maternal height, weight, ethnic group and parity as well as gestational age and sex. Results are expressed as odds ratios (adjOR) with confidence intervals (CI) and population attributable risk (PAR). Results: The table lists the significant variables associated with SB in our population. FGR had the strongest association, with OR 9.46 and PAR 54.1%, followed by African-American (Afr-Am) ethnicity and high BMI. The presence of PE/GH reduced the risk of stillbirth; this association was only significant when FGR was included in the model.