Hypertension May Influence Infant Birth Weight, Preterm Birth Status

James S. McLay, PhD

Research from Scotland is shedding new light on the impact of hypertension and in utero exposure to hypertension mediation on the health of a child.

A team led by James S. McLay, PhD, of the University of Aberdeen and the Royal Aberdeen Children's Hospital, examined more than 250,000 births between 2010-2014. Their findings suggested women with hypertension requiring treatment were more likely to deliver early, but also concluded all women with hypertension—treated or untreated—had a similar risk of having low birth weight babies.

To further expound upon the available data pertaining to in utero exposure and the impact of hypertension medication, investigators conducted a retrospective cohort analysis of data from the Community Health Index, which represents all patients using the National Health Service in Scotland.

A total of 265,488 children were eligible for inclusion and investigators divided them into 4 different groups to assess differing hypertensive presentations during pregnancy. These groups included those with exposure to antihypertensive medication during pregnancy, those with late-onset hypertension, those with untreated hypertension, and an unexposed comparison group.

McLay and colleagues also established multiple outcome measures for the study including preterm birth, low birth weight, emergency Cesarean section, and being small for gestational age. Investigators defined preterm birth as birth on or before 36 weeks, low birth weight as a birth weight of less than 2500 grams, and being small for gestational age as having a birth weight below the tenth percentile of the population.

Of the 265,488 included in the study, 2350 were exposed in utero to antihypertensive medication, 4391 were exposed to treated late-onset hypertension, and 7971 were exposed to untreated hypertension during pregnancy. The most common antihypertensive exposure was to β-blockers (4003 children; 58.66%), a combination of more than 1 antihypertensive medication (1403 children; 20.53%), or calcium channel blockers only (558 children; 8.18%).

Compared to unexposed groups, investigators observed patients all 3 patients groups including untreated hypertension (aRR, 1.63; 99% CI, 1.51—1.75), exposure during pregnancy (aRR, 1.45; 99% CI, 1.27–1.64), and late-onset hypertension (aRR, 2.16; 99% CI, 1.98–2.37), were at an increased risk of emergency Cesarean section than the unexposed control group.

In analyses comparing outcomes with the untreated hypertensive group, a slight decrease in risk of emergency Cesarean section was noted in the antihypertensive exposure group (aRR, 0.83; 99% CI, 0.71—0.96), but an increased risk compared to the late-onset group (aRR, 1.24; 99% CI, 1.11–1.39).

Untreated hypertension (aRR, 1.15; 99% CI, 1.01—1.30), exposure during pregnancy (aRR, 3.12; 99% CI, 2.68–3.64), and late-onset hypertension (aRR, 2.71; 99% CI, 2.41–3.05) were all associated with increased risk for preterm birth compared to the unexposed control group. After adjusting for gestational age, significantly increased risk of low birth weight was associated with untreated hypertension (aRR, 2.01; 99% CI, 1.72–2.36), exposure during pregnancy (aRR, 2.23; 99% CI, 1.79–2.78), and late-onset hypertension (aRR, 2.21; 99% CI, 1.86– 2.62) when compared to the unexposed group.

In regard to size for gestational age, increased risk was noted among those with antihypertensive exposure during pregnancy (aRR, 2.13 [99% CI, 1.81—2.52]), late-onset hypertension (aRR, 1.90 [99% CI, 1.68–2.16]), and untreated hypertension (aRR, 1.50; 99% CI, 1.35–1.66) compared to the unexposed control group.

The team concluded that, though there may be an association between prenatal antihypertensive medication and preterm birth, this observed correlation may reflect the increasing patient hypertension severity which would necessitate treatment. The findings better suggest that hypertension is a key risk factor for low birth weight and preterm birth.

This study, titled “In Utero Antihypertensive Medication Exposure and Neonatal Outcomes: A Data Linkage Cohort Study,” was published in Hypertension