Change in plasma cystyl aminopeptidase (oxytocinase) between 30-34 weeks' gestation as a predictor of pregnancy-induced hypertension.

Ninety-two primigravidas were screened biweekly by measurement of plasma cystyl aminopeptidase from 28 weeks' gestation until delivery. Fourteen developed hypertension with or without proteinuria after 36 weeks. The hypertensive group had significantly higher levels of the enzyme at 30 weeks, although this difference was not significant at 34 weeks. The rise in the hypertensive group was less than 50% between weeks 30-34 in all cases, whereas it was over 50% in all but two of the 43 controls. The difference in the rates of increase of the enzyme and its action on antidiuretic hormone may have some bearing on the subsequent development of hypertension.