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Objectives To determine: 1. whether an alternative definition of gestational hypertension and pre-eclampsia stratifies women according to their risk of maternal and fetal complications; 2. whether pregnancy outcome in women with gestational hypertension differs in the presence or absence of ‘+’ proteinuria; and 3. whether a blood pressure rise of ≥ 30/15 mmHg during pregnancy is associated with adverse outcome in women who remain normotensive.

Design Prospective, nested case–control study.

Setting Community based.

Population Healthy, nulliparous women (n= 1496).

Methods Women recruited into a study investigating serum markers predictive of pre-eclampsia were classified as having gestational hypertension (systolic blood pressure ≥ 140 mmHg with a rise of ≥ 30 mmHg and/or diastolic blood pressure ≥ 90 mmHg with a rise of ≥ 15 mmHg) or pre-eclampsia (gestational hypertension plus proteinuria ≥ 2+on dipstick or > 0.3 g/24 h). Maternal and fetal complications in gestational hypertension or pre-eclampsia were compared with a control group of 223 randomly selected normotensive women. The main outcome measures were severe maternal disease, preterm birth and small for gestational age infant.

Results A stepwise increase in adverse maternal and fetal outcomes occurred in gestational hypertension (n= 117, 743%) and pre-eclampsia (n= 71, 4.8%). Severe maternal disease developed in 26.5% (21.4% severe hypertension alone, 5.1% multisystem disease) of women with gestational hypertension and 63.4% (21.1% severe hypertension alone, 42.3% multisystem disease) of women with pre-eclampsia (OR 4.8; 95% CI 2.4–9.5). Preterm birth and small for gestational age infants were more frequent in gestational hypertension (OR 1.7; 95% CI 0.5–5.4, and OR 2.0; 95% CI 1.0–3.7, respectively) and pre-eclampsia (OR 14.6; 95% CI 5.8–37.8, and OR 2.6; 95% CI 1.2–5.3) than in the normotensive group. Among women with gestational hypertension severe maternal disease was more common in women with ‘+’ proteinuria (41.7%) than in those with no proteinuria (15.9%): OR 3–8; 95% CI 1.5–9.8. Pregnancies were uncomplicated in the 27% of normotensive women who had a rise of ≥ 30 mmHg systolic blood pressure and/or ≥ 15 mmHg rise in diastolic blood pressure.

Conclusions In the nulliparous population studied our definition of gestational hypertension and pre-eclampsia identified women at increasing risk of maternal and fetal complications. In gestational hypertension, the presence of proteinuria ‘+’ was associated with a 3.8-fold increase in severe maternal disease. Normotensive women who have a rise in blood pressure ≥ 30/15 mmHg had uncomplicated pregnancies.