Up to 5 percent of all pregnant women have underlying chronic hypertension, and rates are higher among women who are older, obese or black. Chronic hypertension increases the risk of preeclampsia and abruptio placentae, both of which may result in increased neonatal morbidity and mortality. However, data that identify specific risk factors for preeclampsia and other adverse pregnancy outcomes in women with chronic hypertension are limited. Sibai and colleagues evaluated data from a large multicenter prospective study of pregnant women with chronic hypertension.

The study group included women who were enrolled in a National Institute of Child Health and Human Development study that examined the potential benefits of low-dose aspirin therapy in the prevention of preeclampsia. All patients had chronic hypertension, defined as either systolic blood pressure of at least 140 mm Hg or diastolic blood pressure of at least 90 mm Hg on at least two occasions at least four hours apart before entry into the study or by 20 weeks of gestation. Preeclampsia was defined according to the baseline characteristics. In women with proteinuria at baseline, preeclampsia was defined as elevated levels of serum alanine transferase or elevated diastolic blood pressure, plus severe headaches, epigastric pain or increasing proteinuria. New-onset proteinuria was defined as results of at least +1 on a routine urine dipstick test for protein. Abruptio placentae was diagnosed by clinical findings and placental examination. The women were divided into two groups: those who had proteinuria at baseline and those who did not. Neonatal outcomes that were evaluated included birth before 37 weeks' gestation, birth weight below the 10th percentile for gestational age, admission to the neonatal intensive care unit and neonatal complications.

Of the 763 women included in the study, 381 received low-dose aspirin therapy, and 382 received placebo. Preeclampsia was diagnosed in 193 women (25 percent) and occurred with similar frequency in both groups. However, women with a prior history of preeclampsia, a diastolic blood pressure of 100 to 110 mm Hg early in the pregnancy or a history of hypertension for at least four years were more likely to have preeclampsia. Maternal age, race or urinary protein excretion at baseline were not associated with later development of preeclampsia. Abruptio placentae occurred in 11 women (1.5 percent). The frequency between groups was similar, except for women with preeclampsia, who were three times more likely to develop the condition. In addition, women with preeclampsia at baseline were significantly more likely to have preterm deliveries, to have more infants admitted to intensive care units and to have more neonatal morbidity and mortality. Similar neonatal outcomes were found in women with proteinuria at baseline. In addition, these women also had more infants who were small for gestational age.

The authors conclude that the incidence of preeclampsia is significantly higher in women who have a previous history of the condition, hypertension lasting at least four years or a diastolic blood pressure of at least 100 mm Hg early in the pregnancy. These findings are consistent with conclusions of earlier studies. Infants born to women with preeclampsia were found to have more complications, a finding that is also similar to previous studies. Of interest was the finding that neither black race nor advanced maternal age was a risk factor for superimposed preeclampsia. This finding differs from previously published studies. The presence of proteinuria early in the pregnancy appears to be a separate risk factor for adverse neonatal outcomes and underscores the importance of preconception counseling, screening and medical follow-up in patients with chronic hypertension.