Girl babies likely for big IVF mums

Heavier women are more likely to have baby girls after IVF treatment, and boys are more common among lighter mums, new Australian research suggests. But Western Australian specialists behind the small study say while the data is "fascinating'' they don't advise prospective parents to change eating habits in the hope of changing their child's gender. "It's very interesting indeed to see such a clear gender trend, and we understand it might be quite alluring to couples who desperately want a girl or a boy, but we still need to look at it on a larger scale,'' said study leader Dr James Stanger, an embryologist at Pivet Medical Centre in Perth.

Dr Stanger analysed the clinic's database over the past five years to look at trends in body mass index (BMI) and baby's sex among the 800 children born. "I found that women who were very thin, with a BMI under 20, were more likely to have boys, with about six boys to every four girls,'' Dr Stanger said. "And women who were overweight, with a BMI over 30, were more likely to have girls by the same rate.'' The findings, presented at a fertility conference in Brisbane last month, showed no gender bias among women in the middle weight range.

Dr Stanger said it was possible that the additional weight had an impact on how embryos implant or the rate at which they grow in the womb. "We know that male embryos grow faster than female embryos by about half a day so it may be that male embryos are growing faster or female embryos are being slowed down and held back in the lower carbohydrate environment usually seen in thinner women,'' he said. "Or it could be something to do with the implantation, or the inactivation of the X chromosomes, but this all requires more investigation.''

He said that if the findings prove true in bigger studies then they may have implications for both IVF and natural conception.
Professor Michael Chapman, a spokesman for the Fertility Society of Australia, said gender biases had been linked to certain diets and environments, but most proved false in bigger studies. "It's certainly an interesting observation, and there might be something in it, but I certainly wouldn't be recommending that women rush out and go on a crash diet because they'd prefer a boy,'' Prof Chapman said.