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The Connection Between Fertility and Weight

Could Just Being Overweight Make Getting Pregnant More Difficult?

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Updated October 28, 2010

Losing weight (or gaining weight) may help increase your fertility.

Being under or overweight can impact your fertility. Losing weight (or gaining weight) may help increase your fertility.

Photo © User asifthebes from Stock.xchng

While studies connecting obesity to anovulation are not news, a study led by Dr. Van der Steeg, a medical researcher at the Academic Medical Center in The Netherlands, shows that even women who regularly ovulate experience sub-fertility when their BMI (body mass index) is in the overweight or obese category. Someone experiencing sub-fertility has a lower than normal chance of becoming pregnant, but unlike women suffering from infertility, spontaneous pregnancy is still likely.

In layman’s terms, they found that women with regular cycles, and otherwise no obvious fertility problems, still have a hard time getting pregnant if they are overweight. They also found that the more overweight the woman is, the lower her chances of pregnancy.

Weight and Fertility

The study looked at a group of women who were defined as being sub-fertile. They looked at the relationship between their difficulty becoming pregnant, and their BMI.

(You can figure out your BMI using an online calculator like this one.)

A normal BMI is considered to be between 18.5 to 24.9. Anything over 25 is considered to be overweight, and a BMI over 30 is defined as obese.

For every BMI unit over 29, chance of pregnancy fell by 4%.

In the study, they found that for every BMI unit over 29, the chance of pregnancy was reduced by four percent, when compared to women with BMI’s between 21 to 29. Women who were severely obese, with BMI’s between 35 to 40, had a 23% to 43% less chance of achieving pregnancy compared to the below 29 BMI women.

It’s important to mention that the researchers did not prove that losing weight will increase the chances of pregnancy. However, it would seem that losing weight could help. Entering pregnancy at a normal weight is healthier in any case, and can reduce the risk of some pregnancy complications, like gestational diabetes. (A BMI between 25 to 29.9 before pregnancy doubles the risk, while a BMI over 30 triples the chance.)

PCOS and Weight

But just because a relationship between weight and fertility has been found, it doesn’t mean your doctor should ignore further testing if you happen to be overweight and are having difficulty conceiving. It could be any number of factors, besides the weight.

In fact, PCOS (polycystic ovarian syndrome), one of the more common causes of infertility, has been connected to trouble with gaining and subsequently losing weight. In other words, the very thing that is causing fertility problems may also be why you’re having trouble losing weight or maintaining a healthy BMI.

If a PCOS diagnosis is made, treating the PCOS can help with the weight problem. Women with PCOS who have been treated with Glucophage (metformin), an insulin resistance medication used off label in the treatment of PCOS, may have an easier time losing weight while on the drug, than without.

Sources:

Jan Willem van der Steeg, Pieternel Steures, Marinus J.C. Eijkemans, J. Dik F. Habbema, Peter G.A. Hompes, Jan M. Burggraaff, G. Jur E. Oosterhuis, Patrick M.M. Bossuyt, Fulco van der Veen and Ben W.J. Mol. "Obesity affects spontaneous pregnancy chances in subfertile, ovulatory women." Human Reproduction Advanced Access. December 11, 2007. Accessed February 4, 2008.

Obesity Reduces Chances Of Spontaneous Pregnancy In Women Who Are Subfertile But Ovulating Normally. ScienceDaily.com. Accessed February 4, 2008. http://www.sciencedaily.com/releases/2007/12/071211233947.htm

Gestational Diabetes. CareFirst BlueCross BlueSheild. Accessed February 4, 2008. http://carefirst.staywellsolutionsonline.com/Library/Encyclopedia/85,P00337

Robert L. Barbieri. "Metformin for the Treatment of Polycystic Ovary Syndrome." Obstetrics & Gynecology 2003;101:785-793. Accessed February 4, 2008.

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