A team of US researchers based at Boston University have found that women who have IVF treatment are more likely to have high blood pressure during pregnancy than women who conceive naturally.

The study, published last week in the journal Fertility and Sterility, links IVF treatment to two conditions - gestational hypertension and pre-eclampsia - both of which are characterised by high blood pressure during pregnancy, affecting the mother and unborn baby.

Pre-eclampsia, also characterised by protein in the urine, accounts for about 15 per cent of premature births. The babies are not only premature but also often 'small for dates' because of growth problems, according to BBC News Online.

The researchers, lead by Dr Allen Mitchell, director of Boston University's Sloane Epidemiology Centre, interviewed over 5,000 recent mothers about any unusual symptoms during pregnancy, including gestational hypertension and pre-eclampsia, and whether or not they underwent any IVF treatment.

In women who had undergone IVF treatment, they found that the risk of gestational hypertension was 90 per cent higher, and the risk of pre-eclampsia more than twice as high. However, after taking into account for other factors linked to these conditions, such as number of previous pregnancies, weight and having multiple births, these risks dropped to just 30 per cent and 20 per cent respectively.

The researchers concluded that the increased risk of gestational hypertension and pre-eclampsia in women who underwent IVF treatment was mostly explained by the fact that such fertility treatment increases the chances of multiple births.