Predictors of ratio of placental weight to fetal weight in multiethnic community

Abstract

Objective: To determine whether placental ratio is influenced by maternal ethnic origin, obesity, hypertension, and haematological indices of iron deficiency anaemia.

Design: Observational study.

Setting: District general hospital in Birmingham.

Subjects: 692 healthy nulliparous pregnant women, of whom 367 were European, 213 Asian, 99 Afro-Caribbean, and 13 of other or undocumented ethnic origin.

Main outcome measures: Placental ratio and maternal body mass index, blood pressure, and haematological indices.

Results: Though birth weight and placental weight were lower in Asian women than in other groups, mean placental ratio was similar in Asian (19.5% (SD 3.3%)), European (20.0% (4.0%)), and Afro-Caribbean women (20.4% (5.3%)). Gestational age at birth was the main predictor of placental ratio in the univariate analysis (r = -0.34, P < 0.001) and multivariate analysis. The only other significant predictor of placental ratio in multivariate analysis was maternal body mass index, which was positively associated with placental ratio (r = 0.1, P = 0.01). Mean (SD) placental ratio was not significantly higher in women who developed gestational hypertension (20.4% (4.5%)) and pre-eclampsia (23.3% (7.3%)) than in normal women (19.8% (3.8%)). No evidence of a relation between placental ratio and first antenatal visit haemoglobin concentration or mean cell volume was detected, and placental ratio was not associated with change in mean cell volume during pregnancy or with third trimester serum ferritin concentration.

Conclusions: These data do not support the proposed association between poor maternal nutrition and increased placental ratio. The association between high placental ratio and adult hypertension may be confounded by genetic and environmental factors associated with maternal obesity (and possibly maternal hypertension).