HIV positive women find it tougher to conceive

But it offers brighter news to HIV positive men who want to father a child.

The research, carried out in France, found that only one out of ten HIV positive women given fertility treatment managed to get pregnant.

The precise reason why this is happening is unclear, but experts say a variety of factors could be at work.

They say that women who have had other sexually-transmitted infections such as gonorrhoea or chlamydia, which can harm fertility, may be more vulnerable to catching HIV when they have sex with an infected partner.

The virus itself - or perhaps anti-retroviral drugs taken to keep it under control - may also be having a detrimental effect on fertility.

Many more couples which include an HIV positive man or woman are now attempting to have babies.

'Sperm washing'

The wide use of modern anti-retroviral drugs has extended the lifespan of HIV patients, and modern techniques have radically reduced the risk of transmission from father to mother, or mother to child.

The research, published in the journal Human Reproduction, was carried out by Dr Jeanine Ohl at the Centre d'AMP de Strasbourg.

They carried out assisted reproduction techniques on 57 couples in which at least one partner had HIV.

Sperm from the HIV positive men was "washed" to virtually eliminate the chance of the virus being transmitted.

A third of the 39 couples in which the man was HIV positive managed to conceive a baby this way.

However, only one of the HIV positive women became pregnant, even though standard and normally highly successful IVF techniques were used.

'Surprised'

Dr Ohl said: "I was very pleased by the good results for men, but surprised at the poor results for women, which I did not expect.

"Some research has found evidence of premature ovarian failure in infected women although this would need confirming in a larger study.

"On the other hand, in developing countries young infected women become pregnant easily. We have to determined whether the virus has created an additional negative factor."

Dr Simon Gregson, from Imperial College London, has studied the fertility of HIV positive women, and says there is now firm evidence that they find it harder to conceive.

He said: "Some studies have suggested that fertility is reduced by as much as 30% to 40%.

"It is possible that the virus is more easily transmitted to a woman who has had an STD which has already damaged her fertility.

"But the virus itself may be causing an extra effect."