The number on the scale may play a surprising role in your pregnancy timetable, according to a new study about obesity and infertility.


Does being overweight interfere with fertility?

Packing extra pounds on your frame can disrupt the delicate balance of hormones that influence ovulation and fertilization, reducing your chances of getting pregnant.

Here's why: Extra fat cells don't just make your jeans feel tighter, they also produce a steady stream of the hormone estrogen. The result? "It's almost like being on a low-dose birth control pill," says Steven J. Ory, MD, immediate past president of the American Society for Reproductive Medicine and a reproductive endocrinologist in private practice in Margate, Florida. Low, constant levels of estrogen in turn suppress other hormones, most notably LH (luteinizing hormone) and FSH (follicle-stimulating hormone), which are needed to trigger ovulation.

Being overweight or obese also increases your risk of developing polycystic ovarian syndrome (PCOS), a complex condition where a hormone imbalance causes women to produce too much testosterone, a male hormone that can shut down ovulation at those high levels.

If I'm ovulating normally, am I still at increased risk of infertility?

Yes, according to a new study published in the journal Human Reproduction. Although it's well known that women who weigh too much may have problems ovulating -- and therefore, difficulty getting pregnant -- this study found that even obese women who ovulate normally were significantly less likely to conceive than normal-weight women.

Dutch researchers tracked more than 3,000 couples trying to conceive and found that for every body mass index (BMI) unit above 29, a woman is about four percent less likely to conceive than women with BMIs between 20 and 29 -- the equivalent impact that aging one year would have on fertility. (BMI is a ratio of your height to weight; normal-weight women have a BMI of 18.5-24.9; overweight women have a BMI of 25-29.9 and obese women have a BMI of 30 or greater).The heavier a woman was, the greater her infertility risk.

Researchers suspect that extra weight may impact other hormone systems that help with fertilization (so even if you ovulated, your egg could still run into trouble getting fertilized).

Is there an ideal weight for getting pregnant?

Having a normal-range body mass index (BMI) of 18.5-24.9 is the healthiest way to start trying to conceive, although not all women who are overweight or obese experience infertility, and many may get pregnant soon after they start trying.

If you're concerned about your weight, know that you don't need to pull off a Biggest Loser-level loss to improve your fertility and health. Research shows that losing as little as five to 10 percent of your body weight (that's 8.25 to 16.5 pounds for someone who weighs 165 pounds) can be enough to help rebalance hormones to boost your odds of conceiving.

If you are overweight or obese when you become pregnant, it's important to stay on track with prenatal appointments and tests to track your blood pressure and sugar levels. Women who are overweight during pregnancy are more likely to develop conditions like high blood pressure (preeclampsia) and gestational diabetes. Their babies are also more likely to be extra large, to have certain birth defects, and to need to be delivered via cesarean section. Talk to your doctor about making nutritious food choices and doable exercise plans so that you can have a healthier pregnancy and baby.

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