Stillbirths are devastating, cannot be predicted, and often occur without a clear cause. The recognition of fetal growth restriction (FGR) as one cause can lead to well-timed delivery and improved outcomes. This study was performed to investigate the role of demographic, social, and medical risk factors known at the beginning of pregnancy and those appearing as pregnancy progresses and their contributions to the incidence of stillbirths.
Data included maternal demographic, medical, and social characteristics and fetal or neonatal characteristics. The presence of intrauterine growth restriction was established based on a birth weight below the 10th weight-for-gestational-age centile. Stillbirth was defined as a neonate born after the 24th week of pregnancy who did not breathe or show any signs of life. The independent and multiple variable effects of variables on stillbirths were assessed in Poisson regression models.
From 92,218 singleton pregnancies, 389 were stillbirths, for a stillbirth rate of 4.2 per 1000 births. Stillbirth rates were increased in the first as well as third and later pregnancies compared with second pregnancies and those in mothers of African, African Caribbean, and South Asian ethnic origin. Social factors with significant associations included deprivation and unemployment of the mother or her partner. Obesity, active and passive smoking, lack of antenatal folic acid, initiation of prenatal care after 13 weeks, history of mental health problems, diabetes, and prior stillbirth increased the risk. In the current pregnancy, preeclampsia and antepartum hemorrhage were strongly associated, but gestational diabetes was not. The strongest factor was FGR, with a relative risk (RR) of 4.0 when FGR was detected antenatally, but 8.0 when FGR was undetected. The overall stillbirth rate of 4.2 per 1000 births was a composite of 2.4 per 1000 (185/76,356) in pregnancies without FGR and 16.7 per 1000 (195/11,697) in pregnancies with FGR. Of pregnancies with FGR, the stillbirth rate for cases detected antenatally was 9.7 (35/3601) compared with 19.8 (160/8096) for undetected cases. The overall stillbirth rate was higher in mothers who smoked (5.8 vs 3.8/1000 births), but this was only in pregnancies with FGR (13.0); the risk of stillbirth in pregnancies without FGR (3.7) was similar to that for nonsmoking mothers (3.8).
Obesity, preexisting diabetes, history of mental health problems, and antepartum hemorrhage in the index pregnancy were associated with an increased risk of stillbirth. Active smoking was associated with an increased risk of stillbirth (adjusted RR, 2.5), but the RR was 5.7 for pregnancies with FGR. No association was found between passive smoking and stillbirth unless FGR was also present (RR, 10.0). The risk of stillbirth was increased for all pregnancies with FGR, but was highest when the mother did not smoke (RR, 7.8). The highest population-attributable risks were associated with FGR, primiparity, and antepartum hemorrhage.
Although several risk factors for stillbirth can be ascertained early in pregnancy, the main factor is FGR, which is not usually predicted or recognized antenatally. The findings indicate the importance of improving current strategies and protocols for improved surveillance of fetal growth antenatally. Early detection of fetal growth problems can reduce the risk of stillbirth and must become a key indicator of safety and effectiveness in antenatal care.
West Midlands Perinatal Institute (J.G., V.M., M.W., A.M., A.F.), Birmingham, United Kingdom; and University of Warwick Medical School (J.G.), Coventry, United Kingdom