Risk factors for pre-eclampsia in nulliparous women

Source: Sibai BM, Gordon T, Thom E et al: Risk factors for preeclampsia in healthy nulliparous women: a prospective multicenter study. Am J Obstet Gynecol 1995; 172: 642-648

Summary: Canadian Medical Association Journal 1996; 154: 207

Nulliparous women account for roughly 75% of cases of pre-eclampsia, and women with multiple fetuses, chronic hypertension, insulin-dependent diabetes mellitus and a history of pre-eclampsia or poor pregnancy outcome are also considered to be at increased risk for pre-eclampsia. Tests to identify women at increased risk are often invasive or expensive or require special expertise that precludes their routine use. Researchers at seven clinical centres in the United States investigated the effect of low-dose (60 mg/d) acetylsalicylic acid (ASA) on the frequency of pre-eclampsia in a randomized trial involving 2947 healthy nulliparous women. They also evaluated demographic and clinical characteristics that might predict predisposition to pre-eclampsia.

Eligible participants had had no previous pregnancies of 20 weeks or longer, were carrying one fetus of 13 to 27 weeks' gestation, had a blood pressure of less than 135/85 mm Hg and had no proteinuria. Potential risk factors assessed were maternal height, prepregnancy weight, race, marital status, previous abortion or miscarriage, years of education, tobacco and alcohol use, systolic, diastolic and mean arterial blood pressures at baseline and gestational age of the fetus. Blood pressure, maternal relative weight and urine protein levels were measured at normally scheduled prenatal visits. Participants were considered to have pre-eclampsia if they had hypertension and proteinuria on two occasions at least 4 hours apart.

Pre-eclampsia was diagnosed in 156 (5.3%) of the women. A significant association (p < 0.001) was found between systolic blood pressure at the time of treatment assignment and pre-eclampsia: the incidence of pre-eclampsia was 2.8% among patients with a systolic pressure of less than 100 mm Hg and 8.9% among those with a systolic pressure of 120 to 134 mm Hg. Diastolic and mean blood pressures were less predictive. Prepregnancy weight relative to desirable weight for height was a strong predictor of pre-eclampsia (p < 0.001): an increase in risk was evident at a threshold of about 120% of desirable weight, and the greatest overall incidence (11.3%) was among women at 140% or more of their desirable weight. Women with a history of abortion or miscarriage were at lower risk of pre-eclampsia: the higher the number of previous pregnancies the lower the risk (p = 0.054). Women who smoked during pregnancy or quit just before becoming pregnant had significantly lower incidence rates of pre-eclampsia (3.7% and 2.7%, respectively) than those who never smoked or who quit a year or more before becoming pregnant (5.9%) (p < 0.05). Race, alcohol use, educational and marital status, maternal age and height were not found to affect risk. There were no significant differences between the low-dose ASA group and the placebo group.

The researchers concluded that predictive variables should be taken into account by practitioners counselling nulliparous women and by investigators designing trials of pre-eclampsia prophylaxis.

| CMAJ January 15, 1996 (vol 154, no 2) |