CHICAGO Obesity decreases the chances that a woman will get pregnant, and the more obese she is, the worse her prospects of conception, Dutch researchers said on Tuesday.
Researchers at the Academic Medical Center in Amsterdam looked at how obesity affects women who are still ovulating but having trouble with conception.
The study, published in the journal Human Reproduction, included more than 3,000 couples between 2002 and 2004 in 24 hospitals in the Netherlands.
Dr. Jan Willem van der Steeg and colleagues looked at the relationship between fertility in these women and their body mass index, a ratio of weight to height. Women with a BMI of 30 or higher are considered obese.
The women had to be ovulating and have at least one working Fallopian tube, and the men had to have a normal semen analysis.
The researchers found that women with a BMI of 30 or higher had significantly lower probability of becoming pregnant naturally, compared with normal weight women who had BMIs of between 21 and 29.
"In the case of a woman with a BMI of 35, the probability of spontaneous pregnancy was 26 percent lower, and in the case of a woman with a BMI of 40, it was 43 percent lower," van der Steeg said in a statement.
One reason for this may be the hormone leptin, which regulates appetite and energy expenditure and is secreted in fatty tissues.
"It is possible that obese women may have disturbed hormone levels, which decrease the chances of successful fertilization and implantation," he said.
Obesity is already known to disrupt ovulation, and the Dutch study now suggests it can lower pregnancy rates compared with women of normal weight.
However, the researchers did not track the timing and frequency of sexual intercourse, which may have affected the results. Some studies have shown that obesity is linked with less frequent sex and reduced sexual desire.
The researchers said the finding should be tested in further studies, especially given the rising rates of obesity.
"Owing to the fact that more women of child bearing age are becoming overweight and obese, this is a worrying finding," they wrote.
(Reporting by Julie Steenhuysen; editing by Mohammad Zargham)