Pregnant women with very high blood pressure (hypertension) can reduce their blood pressure with antihypertensive drugs, but the most effective antihypertensive drug during pregnancy is unknown. The aim of antihypertensive therapy is to lower blood pressure quickly but safely for both the mother and her baby, avoiding sudden drops in blood pressure that can cause dizziness or fetal distress.
During pregnancy, a woman's blood pressure falls in the first few weeks then rises again slowly from around the middle of pregnancy, reaching pre-pregnancy levels at term. Pregnant women with very high blood pressure (systolic over 160 mmHg, diastolic 110 mmHg or more) are at risk of developing pre-eclampsia with associated kidney failure and premature delivery, or of having a stroke. The review of 35 randomised controlled trials including 3573 women (in the mid to late stages of pregnancy, where stated) found that while antihypertensive drugs are effective in lowering blood pressure, there is not enough evidence to show which drug is the most effective. Fifteen different comparisons of antihypertensive treatments were included in these 35 trials, which meant that some comparisons were made by single trials. Only one trial had a large number of participants. This trial compared nimodipine with magnesium sulphate and showed that high blood pressure persisted in 47% and 65% of women, respectively. Calcium channel blockers were associated with less persistent hypertension than with hydralazine and possibly less side-effects compared to labetalol. There is some evidence that diazoxide may result in a woman's blood pressure falling too quickly, and that ketanserin may not be as effective as hydralazine. Further research into the effects of antihypertensive drugs during pregnancy is needed.