Obese couples have a more difficult time conceiving a baby than couples of normal weight, according to a study published on Tuesday identifying another consequence of putting on too much weight.
Researchers tracked nearly 48,000 Danish couples between 1996 and 2002, including about 7,600 couples with both the man and woman either overweight or obese according to standards set by the World Health Organization.
They measured how long it took couples to conceive a baby once they began unprotected sex in a bid to have a child.
If both the man and woman were obese, their chances of having to wait longer than a year before the woman became pregnant were nearly three times higher than for couples of normal weight, the study found.
If the man and woman were both overweight, their likelihood of waiting longer than a year before pregnancy was 1.4 times higher.
While doctors already knew that extra weight could affect fertility in women and men as individuals, this study looked at what happened to the fertility of couples when both the man and woman were overweight.
Previous research had established that semen quality and levels of reproductive hormones were diminished in overweight men, and that being overweight can harm ovulation, conception and early fetal development in women.
"If a couple is obese or overweight and if they want to have a child, we would advise them to try and lose some weight," lead researcher Cecilia Ramlau-Hansen of Aarhus University Hospital in Denmark and University of California Los Angeles, said in a telephone interview.
"Especially if they have tried to become pregnant for a while and haven't succeeded, then losing weight might help them," Ramlau-Hansen added.
She said the study did not examine whether heavier couples had sex less frequently than normal weight pairs.
"If, for example, the obese couples hardly ever had sex then, of course, the chances of becoming pregnant would be reduced. But we don't know that at all," Ramlau-Hansen added.
The research did not look at whether sterility occurred more often in obese or overweight couples.
"No, we don't think obesity can make people sterile. But we think that the heavier they get, the longer it will take them to become pregnant," Ramlau-Hansen added.
The findings were published in the journal Human Reproduction.
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