The stillbirth rate in pregnancies with fetal growth restriction (FGR) was four times higher than in those with normal growth, and eight times higher in cases where FGR had not been detected antenatally, in a large UK study.

Between June 2009 and May 2011, 92,218 normally formed babies from singleton pregnancies were born across 19 maternity units in the West Midlands. Of these 91,829 were live births and 389 stillbirths (4.22/1,000 births). Around half, 52%, of stillbirths occurred in pregnancies of more than 34 weeks duration.

Data on gestational duration, birth weight adjusted for gestational age, and a range of relevant maternal and pregnancy demographics were collected.

The biggest single association with stillbirth was FGR. Although the overall stillbirth rate was 4.2/1,000 births it was only 2.4/1,000 births in those without FGR but 9.7/1,000 births when FGR was detected antenatally and 19.8/1,000 births when FGR was not detected.

The largest single risk factor was FGR which was present in 37.4% of stillborn babies, followed by maternal smoking without FGR, 9.4%, and maternal obesity (BMI ≥ 30), 8.7%.

Most cases of FGR were only identified after birth (69%). The proportion of cases detected before birth varied widely between maternity units (12.5-50%). Antenatal detection of FGR was assessed using fundal height charts (and ultrasound scans in obese women). Staff training and adherence to protocols appeared to be important here.

FGR and smoking were also found to be significantly associated. In FGR pregnancies passive maternal smoking increased the risk of stillbirth 10-fold, relative risk (RR) 10.0 (95% CI:6.6-15.8, P < 0.01) and was present in 9.1% of all stillbirths.

Multivariable analysis showed the risk of stillbirth was significantly higher in primigravid women, those with parity ≥ 3 RR 1.8 (95% CI:1.3-2.5), and RR 1.6 (95% CI:1.0-2.5) respectively, and obese women RR 1.4 (95% CI: 1.0-2.0) for BMI 30.0-34.9 and RR 1.6 (95% CI:1.1-2.4) for BMI ≥ 35.

Risk of stillbirth was also higher in women with a history of mental health problems, those who were considered economically deprived, had pre-existing diabetes, and from an ethnic minority community.

Stillbirth rates have not fallen significantly in the UK over the past two decades. This large well organised study has shown that many cases are potentially avoidable.

Maternal smoking (passive or active) appears to be an important modifiable variable. However, increased effort in the detection of FGR would appear to be crucial as well.

The authors estimated that early detection of FGR might have prevented 71 (18.2%) of the stillbirths in their study. Scaling this figure up nationally would represent around 600 potentially preventable stillbirths each year.

Dr Chris Barclay

• Gardosi J, Madurasinghe V, Williams M et al. Maternal and fetal risk factors for stillbirth: population based study. BMJ 2013;346:f108