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High blood pressure in early pregnancy 'increases birth defect risk'

Hypertension in early pregnancy increases the risk a woman will have a baby with birth defects, regardless of whether she takes ACE inhibitors or any other antihypertensives, concludes a US study.

ACE inhibitors are known to cause birth defects when taken in the later stages of pregnancy, but the researchers wanted to know if they had a similar effect when taken in the first trimester.

NICE guidelines released in 2010 recommend ACE inhibitors should be stopped if a woman becomes pregnant, preferably within two days, and ideally should be replaced by an alternative antihypertensive before the woman becomes pregnant.

But these findings could prompt a review of the guidelines, after finding that in early pregnancy, it is the hypertension and not the treatment that can raise the risk of birth defects.

This retrospective cohort study, published online by the BMJ, looked at 465,754 mother and infant pairs from the Kaiser Permanente Northern California region between 1995 and 2008.

After adjusting for maternal age, ethnicity, number of children, pre-existing diabetes and weight, researchers found using ACE inhibitors in the first trimester only was associated with a 54% increased risk of congenital heart defects compared with controls who did not have hypertension.

But a similar association, with a 52% increased risk,was seen with other antihypertensive drugs. Presence of hypertension itself during pregnancy – without use of antihypertensive drugs - was associated with a 41% increased risk.

There was no increased risk with ACE inhibitors or other antihypertensives when compared with controls who had hypertension but were not taking medication.

A similar pattern was seen for all serious birth defects.

Dr Ivan Benett, a cardiology GPSI in Manchester, said the results were to a degree reassuring.

‘If a woman became pregnant accidentally and was already on ACE inhibitor, there would be concern about the foetus... now the woman can be cautiously reassured.'

Dr Chris Barry, a GP in Swindon and member of the guideline development group for the 2010 NICE hypertension in pregnancy guidelines, said the findings had implications for the recent NICE recommendation that ACE inhibitors should be discontinued before pregnancy where possible: ‘This paper may - and I stress may - render that recommendation obsolete.'

‘It would seem that, rather than stopping before pregnancy or at its very beginning, the decision can be made in a more leisurely fashion.'

But Dr Chris Arden, a cardiology GPSI in Southampton, said: ‘I'll be still going along with NICE guidance recommending using other drugs.'

BMJ 2011, published online 18 October

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