British researchers have now found that women who are even slightly overweight are less likely to conceive through IVF. Previous research found that being clinically obese is known to affect in vitro fertilization (IVF), conception, pregnancy and birth.
The researchers found that the chance of these women having a live birth through the treatment was cut by 9 percent, while the risk of miscarriage increased by 24 percent.
This is the first time that being overweight - even by just a few pounds - is clearly identified as a risk factor for the outcome of treatment that can cost as much as 5,500 pounds a cycle.
Lead researcher Dr Tarek El-Toukhy, a reproductive medicine specialist at Guy's and St. Thomas' NHS Foundation Trust in London and his colleagues looked at more than 400 women undergoing IVF.
They calculated the patients' body mass index and looked at success rates.
They found that women classed as 'overweight' had a 24 percent extra risk of miscarriage compared with a normal pregnancy, and a 9 percent lower chance of having a baby.
For 'obese' women, the risk of miscarriage was increased by 40 percent and chance of a live birth cut by 20 percent.
"The higher up the (BMI) range, the more likely it is that overall success rate will be reduced," the Daily Mail quoted El-Toukhy as saying.
"To maximise the chance of a successful pregnancy, we are now recommending that women get as close as possible to a healthy weight before starting treatment," he added.
The findings, pooled with the results from 32 other studies which came to the same conclusion, are published in the journal Human Reproduction.