A population-based retrospective cohort study ² (911,685 births between 1995 and 2008), using the Danish Fertility Database assessed the association between exposure to beta-blockers during pregnancy and the risk of adverse pregnancy outcomes. Beta-blocker exposure during pregnancy (n=2459) was found to be associated with increased risk of small for gestational age (SGA) (adjusted OR 1.97, 95% CI 1.75 to 2.23), preterm birth (aOR 2.26, 95% CI 2.03 to 2.52) and perinatal mortality (aOR 1.89, 95% CI 1.25 to 2.84). Analyses were adjusted for socioeconomic and maternal variables. The authors found similar risk profiles for labetalol and other β-blockers.

A retrospective cohort study ³ in Canada compared infant outcomes between mothers with hypertension treated by beta-blockers alone (n = 416) and by methyldopa alone (n = 1000) during pregnancy (all eligible women, women with chronic hypertension and women with gestational hypertension or pre-eclampsia/eclampsia, separately). Multiple logistic regression analyses were performed to adjust for potential confounding. Adjusted odds ratios (aORs) and 95% CIs for infants born to mothers with chronic hypertension with beta-blockers only, as compared methyldopa only, during pregnancy were: SGA < 10th percentile 1.95, 95% CI 1.21 to 3.15.

A systematic review ¹ including 45 studies with a total of 3,733 subjects was abstracted in DARE. Seven trials (6 publications) randomised women with chronic hypertension to therapy or either placebo or no therapy. A further 38 trials randomly allocated women with late-onset hypertension to antihypertensive therapy or either placebo or no therapy (15 trials; 15 publications) or other antihypertensive therapy (23 trials; 20 publications).

A greater mean difference in mean arterial pressure (MAP) with antihypertensive therapy was associated with the birth of a higher proportion of small-for-gestational age (SGA) infants (slope 0.09, standard deviation (SD)=0.03, r²=0.48) and lower mean birth weight (slope -14.49, SD=6.98, r²=0.16); this was found to be significant after exclusion of a paper regarded as an extreme statistical outlier. Over the range of the reported mean difference in MAP, a 10 mmHg fall in MAP was associated with a 145 g decrease in birth weight. Only 16% of the variation in mean birth weight between groups could be explained by the differential fall in MAP between treatment and control groups.

The authors conclude that given the small maternal benefits that are likely to be derived from therapy, new data are urgently needed to elucidate the relative maternal and fetal benefits, and the risks of oral antihypertensive drug treatment for mild-to-moderate pregnancy hypertension.

In an open-label, multicenter trial ⁴ , 2408 pregnant women with mild chronic hypertension were randomized to receive antihypertensive medications (active-treatment group) or no treatment unless severe hypertension (systolic pressure, ≥160 mm Hg; or diastolic pressure, ≥105 mm Hg) developed (control group). The primary-outcome event (composite of preeclampsia with severe features, medically indicated preterm birth at less than 35 weeks’ gestation, placental abruption, or fetal or neonatal death) was lower in the active-treatment group than in the control group (30.2% vs. 37.0%), for an adjusted risk ratio of 0.82 (95% CI 0.74 to 0.92; P<0.001). The percentage of small-for-gestational-age birth weights below the 10th percentile was 11.2% in the active-treatment group and 10.4% in the control group (aRR 1.04, 95% CI 0.82 to 1.31; P=0.76). The incidence of serious maternal complications was 2.1% and 2.8%, respectively (RR 0.75, 95% CI 0.45 to 1.26), and of severe neonatal complications 2.0% vs 2.6% (RR 0.77, 95% CI 0.45 to 1.30). The incidence of any preeclampsia in was 24.4% and 31.1%, respectively (RR 0.79, 95% CI 0.69 to 0.89), and of preterm birth was 27.5% and 31.4% (RR 0.87, 95% CI 0.77 to 0.99).