Maternal blood pressure in pregnancy, birth weight, and perinatal mortality in first births: prospective study

Abstract

Objective: To investigate the relation of diastolic blood pressure in pregnancy with birth weight and perinatal mortality.

Design: Prospective study.

Setting: 15 maternity units in one London health region, 1988-2000.

Participants: 210 814 first singleton births of babies weighing more than 200 g among mothers with no hypertension before 20 weeks' gestation and without proteinuria, delivering between 24 and 43 weeks' gestation.

Main outcome measures: Birth weight and perinatal mortality.

Results: The mean (SD) birth weight of babies born to mothers with no hypertension before 20 weeks' gestation or proteinuria was 3282 g (545 g) and there were 1335 perinatal deaths, compared with 94 perinatal deaths among women with proteinuria or a history of hypertension. Diastolic blood pressure at booking for antenatal checks was progressively higher from weeks 34 to 40 of gestation. The birth weight of babies being delivered after 34 weeks was highest for highest recorded maternal diastolic blood pressures of between 70 and 80 mm Hg and lower for blood pressures outside this range. Both low and high diastolic blood pressures were associated with statistically significantly higher perinatal mortality. Using a linear quadratic model, 94 of 825 (11.4%) perinatal deaths could be attributed to mothers having blood pressure differing from the optimal blood pressure (82.7 mm Hg) predicted by the fitted model. Most of these excess deaths occurred with blood pressures below the optimal value.

Conclusions: Both low and high diastolic blood pressures in women during pregnancy are associated with small babies and high perinatal mortality.

Fig 1

Diastolic blood pressures of women booking for antenatal checks among mothers without chronic hypertension and no proteinuria between 24 and 43 weeks at delivery. Values adjusted for calendar year and women's ethnic group, smoking status, height, weight, age at booking, and Carstairs' deprivation score

Fig 2

Birth weight and highest diastolic blood pressure, unadjusted or adjusted for maternal height and weight, among mothers without chronic hypertension, chronic renal disease, or proteinuria and gestation between 34 and 43 weeks at delivery. Values adjusted for calendar year and women's ethnic group, smoking status, height, weight, age at booking, and Carstairs' deprivation score

Fig 4

Perinatal mortality per 1000 live births and stillbirths in relation to highest diastolic blood pressure in mothers and gestation between 24 and 43 weeks at delivery, unadjusted and adjusted for birth weight, among women without chronic hypertension and no proteinuria (numbers of deaths are in brackets). Values adjusted for calendar year and women's ethnic group, smoking status, height, weight, age at booking, and Carstairs' deprivation score

Fig 5

Perinatal mortality per 1000 live births and stillbirths in relation to highest diastolic blood pressure in mothers and gestation between 24 and 43 weeks at delivery, including women with proteinuria and chronic hypertension. Values adjusted for calendar year and women's ethnic group, smoking status, height, weight, age at booking, and Carstairs' deprivation score

Fig 3

Birth weight and rise in blood pressure after booking for antenatal checks, by blood pressure at booking and gestation between 34 and 43 weeks at delivery, among women without chronic hypertension and no proteinuria. Values adjusted for calendar year and women's ethnic group, smoking status, height, weight, age at booking, and Carstairs' deprivation score