Placental abruption and placental weight - implications for fetal growth.

OBJECTIVE: Placental abruption is associated with increased risks of preterm delivery and fetal growth restriction. As abruption is apparently a disease of the placenta, the extent to which abruption impacts the growth and development of the placenta remains poorly understood. We reasoned that a study of fetal growth and placental growth in relation to abruption might provide some clues to understanding the process through which placental abruption impacts fetal growth.

DESIGN: Multicenter, prospective cohort study.

SETTING: USA, 1959-1966.

POPULATION: A total of 38 684 pregnancies resulting in singleton live births (22-44 weeks).

MAIN OUTCOME MEASURES: Risk ratio of placental ratio <10th centile for gestational age in relation to abruption. Placental ratio was defined as the difference between placental weight and birthweight divided by birthweight (and expressed per 100 births).

RESULTS: Mean birthweight and placental weight were, on average, lower among abruption than nonabruption births, but this difference was observed only among births at <37 weeks. Births with placental ratio <10th centile were lower among abruption than nonabruption births at 22-36 weeks (risk ratio 0.4, 95% CI 0.2-0.8), but not at term (risk ratio 0.9, 95% CI 0.6-1.2).

CONCLUSIONS: In normal pregnancies, fetal weight and placental weight may operate under independent mechanisms, but in the presence of abruption, the associations appear largely through an interaction of both the maternal and fetal environments. This study underscores the importance of examining both the maternal and fetal compartments - and their interactions - to fully understand the consequences of abruption on fetal growth impairment.