Relation of antepartum stillbirth to birthweight and gestational age: Prospective cohort study

To investigate the incidence of antepartum stillbirth in relation to the distribution of neonatal/fetal weight for different gestational ages.

Prospective observational cohort study.

Obstetric ultrasound departments in two UK maternity hospitals.

168 966 women with singleton pregnancies attending for routine antenatal care.

We examined the incidence of antepartum stillbirths, within different birthweight and fetal weight percentile subgroups, conditioning for gestational age.

Incidence of antepartum stillbirth.

The risk of stillbirth progressively increased for lower birthweight. Considering the 25-75th percentile as the reference category, the relative risks for stillbirth at <37 weeks' gestation were 7.6 (95% confidence interval [CI] 5.7-10.2) <1st percentile, 2.6 (95% CI 1.8-3.7) 1 to 10th percentile, 1.4 (95% CI 0.9-2.1) 10 to 25th percentile, 0.8 (95% CI 0.4-1.5) 75 to 90th percentile, 0.8 (95% CI 0.4-1.7) 90 to 99th percentile, 0.9 (95% CI 0.3-2.5) >99th percentile. The respective values for births at ≥37 weeks' gestation were 5.0 (95% CI 2.9-8.9), 2.1 (95% CI 1.4-3.3), 1.4 (95% CI 0.9-2.1), 1.2 (95% CI 0.7-1.8), 1.0 (95% CI 0.6-1.8) and 4.0 (95% CI 1.8-9.3). The incidence of stillbirth in ongoing low-risk singleton pregnancies gradually increases for smaller fetuses at any gestational point. The higher incidence (5.56%) was evident for fetal weight <1st percentile between 24 and 28 weeks' gestation.

Fetal weight and the weight of the stillborn have a continuous association with the incidence of antepartum stillbirth which is affected by gestational age.