Risks of having a baby boy

Women whose first child is a boy are more likely to have a miscarriage in later pregnancies, according to research.

Scientists believe this may be because some mothers have an immune reaction to male babies which causes problems when they are expecting more children.

At a fertility conference yesterday they unveiled a treatment that could prevent women's bodies rejecting male infants.

The reaction takes place because baby boys secrete proteins linked to the male Y chromosome, which may cause the mother's immune system to form antibodies to try to fight off the 'invader'.

The first pregnancy survives because the foetus is strong enough to resist by the time the immune response begins. But experts say women's bodies may 'remember' what has happened and form similar antibodies early on in their next pregnancy, causing them to miscarry.

Researchers from Rigshospitalet Fertility Clinic in Copenhagen, Denmark, studied nearly 200 women who had suffered at least three miscarriages after a healthy pregnancy.

They found that only 54.4 per cent of those who gave birth to a boy in their first pregnancy had been able to have a second baby.

This compared with nearly 75 per cent of women whose first child was a girl, the annual conference of the European Society of Human Reproduction in Madrid heard yesterday. Dr Ole Christiansen, who led the research team, said: 'Giving birth to a son is already known to carry a higher risk of pregnancy complications, so we wanted to assess the impact of the gender of the first child on the outcome of subsequent pregnancies.

'Among my patients, I have at least 50 women who never had a second child after the first birth of a boy, whereas only about 20 did not experience another birth after having a girl.

'There are patients in both groups who will never have another child, but the risk is greater if you have a boy first.'

To test his antibody theory, Dr Christiansen used a blood product called immunoglobulin that is known to help stabilise the immune system.

About 90 women who had had several miscarriages participated in the study, with half receiving transfusions of immunoglobulin and half a placebo. Two-thirds of the women who had the active transfusion went on to have another baby, compared with only a quarter of those in the untreated group.

The transfusions are given weekly during the first three months of pregnancy until the foetus is firmly established in the womb - making it less likely to be affected by the antibodies.

Dr Christiansen added: 'We need more research. But if our theories about the immune system in women reacting to baby boys are correct, then it seems we already have an effective treatment to help them overcome the problem.'