Antihypertensive drug therapy for mild to moderate hypertension during pregnancy
What is the issue?
The aim of this review was to determine the benefits and adverse effects of blood pressure-lowering drugs (antihypertensive drugs) for pregnant women with mild to moderate hypertension (high blood pressure). The other aim was to assess the benefits and adverse effects of these drugs for their babies.
Why is this important?
During pregnancy, up to one in 10 women have blood pressure readings that are above normal. For some women, their blood pressure remains slightly high (termed 'mild to moderate high blood pressure'), with no apparent complications. Some of these women go on to develop very high blood pressure. Very high blood pressure can result in a medical emergency if it affects the woman's organs (such as her liver, or brain in the form of a stroke). Also, it can seriously affect the growth and health of her baby.
Drugs that lower blood pressure are used to treat mild to moderate high blood pressure, in the belief that this treatment will prevent the blood pressure from continuing to rise. Over the years, information from good quality research studies has been contradictory, so we cannot be sure if this drug treatment is worthwhile.
What evidence did we find?
This Cochrane Review is an update of a review that was first published in 2001 and updated in 2007 and 2014. We searched for randomised controlled trials in September 2017, and this review now includes data from 58 trials involving more than 5900 women. A total of 31 trials with 3485 women compared a number of different blood pressure-lowering drugs to a placebo or no treatment. There were a further 29 trials involving 2774 women which compared one blood pressure-lowering drug with another one.
The evidence showed that treating pregnant women who had moderately raised blood pressure with blood pressure-lowering drugs probably halved the number of the women developing severe high blood pressure (20 trials, 2558 women). However, blood pressure-lowering drugs probably had little or no effect on the risk of the baby dying (29 trials, 3365 women), and there is insufficient data on maternal deaths to make a judgement on whether this risk is lowered (five trials, 525 women).
The use of blood pressure-lowering drugs may have little or no effect on the number of the women developing pre-eclampsia (23 trials, 2851 women), or the number of women who had to change drugs because of side-effects (16 trials, 1503 women).
We found no difference in the number of babies born preterm, that is before 37 weeks (15 trials, 2141 women). There was also no difference in the number of babies born small for their gestational age (21 trials, 2686 babies).
The quality of the evidence was mostly moderate (but for pre-eclampsia it was low). This was due to a number of small studies, and problems with the way the studies were undertaken.
The available evidence is still insufficient to demonstrate if there is any antihypertensive drug that is better than another. However, beta blockers and calcium channel blockers seem to be better than the alternative drugs for blood pressure control.
What does this mean?
More research is needed in order to confirm the true effect of antihypertensive drugs in mothers and in their babies, and to identify the drug which would be best.
Antihypertensive drug therapy for mild to moderate hypertension during pregnancy reduces the risk of severe hypertension. The effect on other clinically important outcomes remains unclear. If antihypertensive drugs are used, beta blockers and calcium channel blockers appear to be more effective than the alternatives for preventing severe hypertension. High-quality large sample-sized randomised controlled trials are required in order to provide reliable estimates of the benefits and adverse effects of antihypertensive treatment for mild to moderate hypertension for both mother and baby, as well as costs to the health services, women and their families.
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