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

Objectives: To investigate the incidence of antepartum stillbirth in relation to the distribution of neonatal/fetal weight for different gestational ages.Design: Prospective observational cohort study.Setting: Obstetric ultrasound departments in two UK maternity hospitals.Population: 168 966 women with singleton pregnancies attending for routine ante-nata l care.Methods: We examined the incidence of antepartum stillbirths, within different birthweight and fetal weight percentile subgroups, conditioning for gestational age.Main outcome measures: Incidence of antepartum stillbirth.Results: 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.Conclusion: Fetal weight and the weight of the stillborn have a continuous associa-tion with the incidence of antepartum stillbirth which is affected by gestational age.