April 12, 2018
Women with a history of chronic hypertension are three to five times more likely to have a poor pregnancy outcome than women without past hypertension, even if their blood pressure is normal before 20 weeks gestation, found a retrospective cohort study published April 6 in Obstetrics & Gynecology.
The highest risk occurred among women taking antihypertensive medication, but even women not taking medication (but with a history of chronic hypertension) had triple the risk for stillbirth, neonatal death, respiratory support, low Apgar score, seizures, or cord blood acidemia, although the findings were limited by a nongeneralizable population and some underpowered measures.
"Although the incidence of stillbirth increased across exposure groups 1.3% [control] vs 1.9% [hypertension history but no medication] vs 2.9% [hypertension with medication] this trend was not statistically significant (P=.06) nor was it significant in adjusted analyses," write Mallory Youngstrom, MD, from the Department of Gynecology and Obstetrics at Emory University in Atlanta, Georgia, and colleagues.
"The incidence of neonatal death (measured only in those with liveborn neonates) increased across the exposure groups (P=.03), but in adjusted analyses, the increased odds was only significant for women receiving [antihypertensive] medication."
Compared with women without a history of hypertension, women taking antihypertensive medication also had significantly increased risks for preeclampsia, severe preeclampsia, preterm birth, and an infant small for gestational age after adjustments, but women with a history of hypertension not taking medications did not.
More Than 70% of Women With History of Hypertension Taking Medication
The researchers first identified all singleton births from 2000 to 2014 at the University of Alabama at Birmingham in which the mother had a history of chronic hypertension.
They then compared outcomes among 830 women with a history of chronic hypertension but blood pressure under 140/99 mm Hg before 20 weeks gestation with those of 476 women without chronic hypertension. Mothers with higher blood pressures were excluded, as were pregnancies with fetal anomalies and mothers with any major medical problems besides hypertension and diabetes.
Among the 830 women with a history of chronic hypertension, 74% (618 women) were taking hypertension medication; the other 26% (212 women) were not. Renal disease and diabetes were more prevalent among these women, who also tended to be older and have more obesity than the control group.
The primary outcomes of stillbirth, neonatal death, respiratory support at birth, seizures, an Apgar score of 3 or less, and arterial cord blood with a pH below 7 were collapsed into a composite outcome. In addition, preeclampsia, infants small for gestational age, and preterm birth before 37 and 34 weeks gestation were recorded as secondary outcomes.
The composite primary outcome occurred among 9.9% of women with a hypertension history but not taking antihypertensive drugs, in 14.6% of women who were taking antihypertensive drugs, and in 2.9% of women with no history of hypertension.
In relative terms, after adjustment for nulliparity and a history of preterm delivery, women with chronic hypertension but not taking medication were three times more likely to have a child with one of the primary outcomes than control group women (odds ratio [OR], 2.9). The women taking antihypertension medications had five times the risk seen in women without a history of hypertension (OR, 5).
No significant differences in preeclampsia, preterm birth, or infants small for gestational age occurred between women without a hypertension history and women with a history but not taking medication.
The study's strengths include its population size, having data on blood pressure before and during pregnancy, and including women with confirmed prior diagnoses of chronic hypertension. However, the findings may not be generalizable because the women were mostly black, had obesity, and had a high prevalence of diabetes before pregnancy, and all came from the same institution.
"Therefore, the differences in outcomes may not be solely the result of the presence of chronic hypertension," the authors write. "Although we attempted to control for these factors using logistic regression, the possibility of residual confounding exists."
Further, the low number of women with past hypertension who were not taking medications was underpowered (57%) to "detect a 50% reduction in the risk of the primary perinatal composite outcome in women without hypertension compared with the no medication group."
They were similarly unable to identify statistically significant differences in stillbirth, neonatal death, and perinatal death because the individual occurrences were so few. Similar limitations in power existed for the secondary outcomes.
The study did not note any external funding. The authors have disclosed no relevant financial relationships.