A report in the British Medical Journal claims that the drugs taken by expectant mums for hypertension (angiotensin-converting enzyme or ACE inhibitors) are known to have a toxic effect on unborn babies during the second or third trimesters.
The study, led by Dr De-Kun Li of the Kaiser Foundation Research Institute in California, was undertaken to see if taking the ACE inhibitors during the first trimester could cause birth defects.
The medics examined the health records of 465,754 pairs of mothers and babies in California between 1995 and 2008. They concluded that while the drugs did not cause defects, the underlying hypertension could increase the risk of abnormalities.
High blood pressure raises the risk of a baby having a congenital heart defect by 41 per cent and a neural tube defect by 43 per cent.
Professor Alastair MacLennan, professor and head of discipline of obstetrics and gynaecology at Adelaide University in Australia commented on the study: "For the general public, the message is that to reduce the risks from high blood pressure and diabetes in early pregnancy they should not leave having their family too late in reproductive life, that is over age 35, they should avoid obesity and, if diabetic, they should have good glucose control before trying to get pregnant."