Maternal blood pressure in pregnancy and stillbirth: a case-control study of third-trimester stillbirth.

An immense body of literature on the effects of hypertension on perinatal morbidity and mortality exists, but only a handful of studies have reported adverse outcomes associated with low maternal blood pressure during pregnancy. This study aimed to investigate if there is an increased risk of fetal loss associated with hypotension during pregnancy. A matched case-control study of stillbirth and maternal blood pressure was conducted in which maternal blood pressures for a total of 124 pregnancies culminating in stillbirth were compared with maternal blood pressures in 243 (matched) pregnancies resulting in a liveborn infant. Women whose diastolic blood pressures fell in a borderline range (60 to 70 mm Hg) were consistently at greater risk of stillbirth relative to normotensive pregnancies. Women who had three or more mean arterial pressure values < or = 83 mm Hg during the course of their pregnancy were at nearly twice the risk of stillbirth (odds ratio 1.78; 95% confidence interval [CI] 1.06 to 2.99; P = 0.03). Systolic hypotension was not significantly associated with stillbirth, but proportionately more control women were noted to have systolic hypertension (SBP > or = 130 mmHg) than cases, and the adjusted odds of stillbirth in women who were hypertensive at either their first or last antenatal visit or whose antenatal average SBP was > or = 130 mm Hg were all very close to 0.4 (95% CI 0.37 to 0.43; P = 0.02 to 0.03) relative to normotensives. We concluded that maternal hypotension, particularly borderline hypotension, may be a contributory risk factor for stillbirth. Women with hypertension in pregnancy may now be at a decreased risk of stillbirth as a result of the close care and treatment they receive.