The odds of having a baby via in-vitro fertilisation (IVF) may be lower for obese women than their thinner counterparts, two new studies find. The studies, reported in the journal Fertility and Sterility, add to evidence suggesting that heavy women have a lesser chance of success with IVF.
Research shows that obese women may be less fertile than their thinner peers. But the evidence has been mixed on whether extra kilogramme can affect a woman's odds of having a baby with IVF.
In the new studies, researchers at two different Massachusetts fertility centers found that overweight women were less likely to have a baby after IVF. In one, the birth rate among both overweight and obese women was 23%, versus 42% among women at the lower end of the normal-weight range.
Few obese women have a baby
In the other study, the odds of success were lower only for obese women, and not those who were less overweight. Of 477 women who were moderately obese, 22% had a baby. That compared with 30% of normal-weight women.
And the chances of success dipped with the severity of a woman's obesity. Among the most obese women – about 45kg or more overweight – 15% had a baby.
The lead researcher on that study said there are still questions about the role of a woman's weight in IVF success.
In some past studies, researchers have found that normal-weight and obese women have similar chances of having a baby, said Dr Vasiliki A Moragianni, of Beth Israel Deaconess Medical Centre and Harvard Medical School in Boston.
But most of those studies were much smaller than this one, he said in an email.
No difference for short term weight loss
Dr Moragianni's team had data on 4 600 women who underwent a first-time round of IVF or IVF plus intracytoplasmic sperm injection.
The other study, led by Dr Jorge E Chavarro, included 170 women who had at least one round of fertility treatment at the Massachusetts General Hospital Fertility Centre.
Overall, obese and overweight women were less likely to have a baby, Dr Chavarro's team found. So then the researchers looked at whether short-term weight loss made a difference.
There were 45 women who had managed to shed some pounds before starting their first treatment cycle – typically about 2,5kg. But the researchers found no difference in their chances of having baby, even though those women did tend to produce a higher number of mature, usable eggs.
None of that means weight loss is no use to heavy women undergoing infertility treatment, the researchers say.
Lifestyle changes improves treatment
The fact is, no one is sure what impact weight loss might have, according to Dr Moragianni.
He said there is evidence that weight loss helps obese women who have polycystic ovary syndrome.
"It can certainly be hypothesised that weight reduction and lifestyle changes can improve (infertility treatment) outcomes in obese individuals," Dr Moragianni said.
But clinical trials are needed to actually prove that is true, he added.
Researchers are not sure why heavier women might have less success with infertility treatment. Obesity may affect the quality of the eggs or embryos a woman produces, Dr Moragianni said, and heavy women sometimes have a less receptive uterus versus thinner women. There may also be a role for hormones.
(Amy Norton, Reuters Health, June 2012)
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