If both partners in a couple are overweight or obese, they are more likely to have to wait longer before successfully conceiving a child, according to new research published online in Europe?s leading reproductive medicine journal, Human Reproduction, today (Wednesday 7 March).
Researchers in Denmark studied 47,835 Danish couples between 1996 and 2002 and found that if both partners were obese the chances of the couple having to wait for more than a year before the woman became pregnant were nearly three times higher (2.74) than for a normal weight couple. If both partners were overweight, the likelihood they would have to wait longer than a year was 1.4 times higher.
Cecilia Ramlau-Hansen, who led the study, warned that if further research supported the findings of the study that too much weight could make couples less fertile, this would have major implications for population levels, particularly in parts of the world where obesity and low fertility were, or would become, more common.
?If overweight and obesity actually is a cause of subfecundity, and if the obesity epidemic continues, this reduced capacity to reproduce could become a serious public health problem. Further research in this area is needed,? she said.
Sub-fertility (or subfecundity) is normally defined as a waiting time to pregnancy of more than 12 months from the time a couple starts to have unprotected sex with an intention to conceive.
Earlier research has already shown that weight can affect fertility in both women and men, individually. However, this is the first study to look at the effect on fertility of overweight and obesity in couples. Ms Ramlau-Hansen, a doctoral student in the Department of Occupational Medicine, Aarhus University Hospital, Denmark, who is on a visiting scholarship to the University of California Los Angeles School of Public Health, USA, said: ?Since it is quite common to have couples where both partners are overweight or obese, it is important to have risk estimates for couples rather than individuals.?
The researchers obtained data from the Danish National Birth Cohort, a nationwide study of pregnant women and their offspring, which enrolled more than 100,000 women between 1996 and 2002. The women completed four interviews over a period of two years, giving information for both themselves and their partners on weight, height, previous pregnancies, smoking habits and socioeconomic groups. After excluding all couples where the information was incomplete, where a disease might be affecting the woman?s weight and fertility, or where donated sperm was used, the researchers were left with data on 47,835 couples.
Ms Ramlau-Hansen said: ?In this cohort, we had 6.8% obese men, 8.2% obese women and 1.4% couples where both were obese. The percentages of persons with normal weight were 53% for men and 68% for women.
?We found there was a relationship between the BMI of the couple and their fertility among the men and women in different BMI combinations. We found a higher risk of sub-fertility related to overweight and obesity for both men and women, particularly for couples where both were overweight. Underweight combined with obese partners, especially underweight men, seemed to cause additional pregnancy delays. The combination of an underweight man and obese woman was associated with a risk of sub-fertility nearly four times higher (3.79) compared to a normal weight couple, although we have to treat this figure with caution as there were only 22 couples in this category.?