Correlation between plasma renin activity and birth weight in hypertensive pregnancy.

Plasma renin activity (PRA) was measured in the late third trimester in 26 hypertensive pregnant women and correlated with their infants' birth weights. Seven pre-eclamptics, six chronic hypertensives and 13 chronic hypertensives with superimposed pre-eclampsia were studied. Plasma renin activity was lower in 13 mothers with small for gestational age (SGA) infants (5.2 +/- 0.89 ng/ml per h, compared with 13 mothers with appropriate for gestational age (AGA) infants (16.65 +/- 2.37 ng/ml per h, P less than 0.001. The mean PRA was also lower in mothers with babies weighing less that 2500 g, regardless of gestational age, compared with 11 mothers with babies weighing more than 2500 g, (7.58 +/- 1.61 versus 15.86 +/- 2.73 ng/ml per h, P less than 0.050. Mean PRA was not significantly different in the different hypertensive groups, although women with chronic hypertension appeared to have lower PRA than pre-eclamptics. Our data suggest that in gestational hypertension, low PRA is associated with low infant birth weight, and that late third trimester PRA may therefore identify those at risk for poor fetal outcome.