Thirty-four trials in forty publications were included (2324 women with pregnancy hypertension).
The median sample size was 22 patients per group (range: 3 to 97 women).
Methodological flaws included: no description of randomisation method (70% of studies), no allocation blinding (61%) and no blinding of the outcome assessment (67%).
Mean fall in MAP was 6.3 mm lower among labetolol-treated patients than among the comparison group.
There was no association between beta-blocker type and outcome.
Mild chronic hypertension (2 RCTs, 205 women).
Maternal.
No significant effect was found for beta-blockers on the following maternal outcomes: additional therapy (2 RCTs), developed proteinuria (1 RCT), Caesarean section (1 RCT) and placetal abruption (1 RCT).
Perinatal.
SGA infants: inconsistent effects were found. The only demonstrated effect on perinatal outcomes was an increased incidence of SGA infants in one RCT but this was not found in a second RCT. No statistically significant effect was found on the following perinatal outcomes: perinatal mortality (2 RCTs), prematurity (1 RCT), neonatal hypoglycaemia (1 RCT) and low Apgar scores (1 RCT).
Mild-to-moderate 'late-onset' pregnancy hypertension.
1. Oral beta-blockers versus placebo/no therapy (8 RCTs, 891 women).
Maternal.
Severe hypertension (6 RCTs): beta-blockers significantly decreased the incidence of severe hypertension. The pooled OR was 0.27 (95% CI: 0.16, 0.45). No significant heterogeneity was found (p=0.62).
Additional therapy (6 RCTs): beta-blockers significantly decreased the incidence of additional therapy. The pooled OR was 0.32 (95% CI: 0.21, 0.50). No significant heterogeneity was found (p=0.73).
Admitted prior to delivery (3 RCTs): beta-blockers significantly decreased the incidence of admission. The pooled OR was 0.52 (95% CI: 0.33, 0.83). Significant heterogeneity was found (p=0.0006).
No significant effect was found for beta-blockers on the following maternal outcomes: developed proteninuria (7 RCTs), Caesarean section (6 RCTs), placetal abruption (2 RCTs) and drugs changed because of maternal side-effects (6 RCTs). No significant heterogeneity was found.
Perinatal.
RDS: beta-blockers significantly decreased the incidence of RDS. The pooled OR was 0.33 (95% CI: 0.13, 0.85). No significant heterogeneity was found (p=0.93).
No significant effect was found for beta-blockers on the following perinatal outcomes: perinatal mortality (9 RCTs), prematurity (5 RCTs), admission to SCN (4 RCTs), neonatal bradycardia (3 RCTs), neonatal hypoglycaemia (3 RCTs) and low Apgar scores (3 RCTs).
2. Oral beta-blockers versus other drugs (15 RCTs, 959 women).
No significant effect was found for beta-blockers on maternal or perinatal outcomes compared with other drugs.
Severe 'late-onset' pregnancy hypertension (labetolol versus hydralazine or diazoxide, 5 RCTs, 171 women).
Maternal.
Maternal hypotension (4 RCTs): labetolol was associated with significantly less hypotension than other drugs. The pooled OR was 0.13 (95% CI: 0.03, 0.71). No significant heterogeneity was found (p=0.98).
Caesarean section (5 RCTs): labetolol was associated with a significantly lower section rate than other drugs. The pooled OR was 0.28 (95% CI: 0.13, 0.63). No significant heterogeneity was found (p=0.98).
No significant difference was found for beta-blockers versus other drugs on severe hypertension (4 RCTs) or additional therapy (3 RCTs). Data were not suitable for an assessment of other maternal outcomes.
Perinatal.
No significant difference was found for beta-blockers versus other drugs on perinatal mortality (7 RCTs), admission to SCN (2 RCTs), neonatal hypoglycaemia (5 RCTs), neonatal hypothermia (1 RCT), low Apgar scores (5 RCTs) or RDS (3 RCTs). Significant heterogeneity was found for low Apgar scores (p=0.018). This was attributed to one small study. Data were not suitable for an assessment of other perinatal outcomes.
There was no association between beta-blocker type and outcome (results not presented).
No effect of methodological quality, as assessed by allocation blinding on outcome (no results presented), was seen.
Outcome definitions varied considerably, but only for neonatal bradycardia did outcome definition have an impact on treatment effect.
Overall, beta-blocker-induced falls in MAP were associated with less severe hypertension and a borderline increase in SGA infants. No effect on proteniuria was seen.