IVF increases chances of a boy

30.09.2010

Women who conceive through IVF (in vitro fertilisation) are more likely to have a boy, the results of a new study indicate.

Australian researchers studied all the live births that took place following fertility treatment in Australia and New Zealand between 2002 and 2006. They focused specifically on IVF and ICSI (intracytoplasmic sperm injection).

With IVF, a woman's eggs are fertilised with sperm outside the body in a test tube and then placed back inside her. ICSI is very similar, however as the sperm are not motile, one has to be injected directly into the egg.

The researchers wanted to determine if there was a link between the type of fertility treatment and the sex ratio at birth, also known as the secondary sex ratio (SSR). This is defined as the proportion of males in all babies born alive.

They pointed out that over the years, there has been a big increase in the proportion of births from the use of fertility treatment. It has therefore become important to check that this does not result in a serious imbalance of male to female children.

A total of 13,368 babies were born to 13,165 women who underwent single embryo transfer (SET) during the study period. The researchers found that women who underwent IVF had a higher chance of having a boy. In fact, the likelihood of having a boy was between 53% and 56.1% depending on how soon the fertilised egg was put back into the woman's body.

The higher rate of 56% was found among women who had the fertilised egg placed back in their body four days after fertilisation (instead of after two or three days).

However for those undergoing ICSI, the chance of having a girl was slightly higher, with 49% of ICSI babies being boys and 51% girls. The chances of having a boy after a natural conception are around 51%.

"This study provides impetus for further research into the underlying causes and/or associations which determine the survival of different sexes in pregnancy," said study co-author, Jishan Dean, of the University of New South Wales.

However she emphasised that for individual cases, it is acknowledged that the type of clinical problem decides the most appropriate fertility treatment management plan, whether that is IVF or ICSI.

"The result of this study should therefore not be used as a de facto tool for sex selection," she said.

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