The surface area of the placenta and hypertension in the offspring in later life

Hypertension is more common among people who had low birthweight. Birthweight depends on the mother's body size and on the growth of the placenta. We studied a group of 2003 subjects, of whom 644 were being treated for hypertension. They were born during 1934-44 in a hospital that kept detailed records of maternal and placental size. Hypertension was associated with reduced placental weight and surface area. These associations were strongest in the offspring of mothers with below average height or low socioeconomic status. In people whose mothers had below average height (160 cm) the prevalence of hypertension fell from 38% if the placental area was 200 cm² or less to 21% if the area was more than 320 cm² (p=0.0007). In the offspring of tall, middle class mothers, who were likely to have been the best nourished, hypertension was predicted by large placental weight in relation to birthweight. The odds ratio rose from 1.0 if the ratio of placental weight to birthweight was 0.17 or less to 1.9 (95% confidence interval 0.8 to 5.0) if the ratio was more than 0.21 (p for trend =0.03). We conclude that the effects of placental area on hypertension depend on the mother's nutritional state. Poor maternal nutrition may compound the adverse effects of small placental size. In better-nourished mothers the placental surface may expand to compensate for fetal undernutrition. Growth along the minor axis of the surface may be more nutritionally sensitive than growth along the major axis.