MOS HIP: McMaster outcome study of hypertension in pregnancy

The offspring of women with hypertension during pregnancy are at increased risk of low birthweight, preterm birth, diseases of prematurity and death. The risk of developing these outcomes among women with either preeclampsia or chronic hypertension, relative to those with gestational hypertension, is not known.

Prospective cohort study.

A total of 1948 singleton women seen at a large tertiary care obstetrical center, whose blood pressure was greater than 140/90 mm Hg during pregnancy. The four types of hypertension were strictly defined: 864 women (44.4%) had gestational hypertension, 459 (23.6%) isolated chronic hypertension, 501 (25.7%) isolated preeclampsia, and 124 (6.4%) chronic hypertension with superimposed preeclampsia.

The primary outcome of the study was a composite of the diseases of prematurity, need for assisted ventilation for greater than 1 day, or perinatal death. The secondary outcomes were each of those included in the primary endpoint, as well as admission to the neonatal ICU, small for gestational age (SGA) birthweight and preterm birth. We controlled for the effects of other maternal risk factors, such as age, parity, history of preterm delivery, cigarette smoking, pre-pregnancy weight, diabetes mellitus (DM), renal dysfunction, and current use of an antihypertensive agent or prednisone.

For the primary composite outcome, compared to the offspring of women with gestational hypertension, the adjusted odds ratio was 1.9 (95% confidence interval 1.2 to 3.0) in the preeclamptic group and 2.0 (95% confidence interval 1.0 to 4.0) for those with chronic hypertension plus superimposed preeclampsia. Those with preeclampsia were at increased risk for small for gestational age birthweight (odds ratio 2.2, 95% confidence interval 1.5 to 3.1), as were the offspring of mothers who had chronic hypertension with superimposed preeclampsia (odds ratio 2.1, 95% confidence interval 1.2 to 3.8). Similarly, the rate of preterm birth before 32 weeks was highest among the infants of both preeclamptic mothers (28.5%; odds ratio 4.7, 95% confidence interval 2.9 to 7.6) and those with chronic hypertension and preeclampsia (30.5%; odds ratio 3.5, 95% confidence interval 1.8 to 6.7). The perinatal mortality rate was highest in the group of women with chronic hypertension plus preeclampsia (9.2%; odds ratio 3.2, 95% confidence interval 1.2 to 9.1). Other significant risk factors for the primary composite outcome included previous preterm delivery (odds ratio 2.7, 95% confidence interval 1.4 to 5.2), smoking (odds ratio 1.8, 95% confidence interval 1.1 to 3.0) and use of an antihypertensive agent during pregnancy (odds ratio 1.8, 95% confidence interval 1.2 to 2.7). Prednisone use was strongly associated with risk for perinatal death (odds ratio 4.9, 95% confidence interval 1.4 to 17.1).

Relative to women with isolated gestational hypertension, those who develop preeclampsia, either with or without underlying chronic hypertension, experience worse perinatal outcomes. A history of previous preterm delivery and maternal smoking increase the rate preterm birth and major perinatal disease. Antihypertensive and prednisone therapy may be important risk factors for adverse perinatal events, but further research is needed to confirm these findings.