Fetal growth retardation in gestational hypertension: relationships with blood pressure levels and the time of onset of hypertension.

To evaluate the effects of gestational hypertension on fetal growth, we studied the standardized records of 2996 single live-birth pregnancies. Mothers all had documented diastolic blood pressure of less than 85 mmHg before the 16th wk of amenorrhea and no history of pre-pregnancy hypertension or kidney disease. Diastolic blood pressure readings exceeding 84 mmHg were found later in pregnancy in 38.4% of the mothers, and were associated with an increased number of small-for gestational-age infants: 3.2% in mothers whose diastolic blood pressure had never reached 85 mmHg, 6.3% when peak diastolic blood pressure had been in the 85-94 mmHg range, and 8.5% when it had exceeded 94 mmHg (p less than 0.01). In mothers who had had one or more diastolic readings of more than 84 mmHg, and for all peak diastolic pressures, the rate of small-for-gestational-age infants was higher when hypertension had begun early in third trimester (between the 27th and 36th wk), than in the second trimester or later than the 35th wk (10.2% compared to 5.6 and 6.1% respectively, p = 0.02). This temporal reinforcement of the adverse fetal effects of hypertension when it began in the early third trimester was not explained by differences in the incidence of proteinuria or in maternal age, parity, obstetric history or smoking habits.