Body weight extremes affect fertility

According to new research extremes of body weight, being either very thin or obese, may decrease a woman's chance of getting pregnant through in vitro fertilization (IVF). During IVF, a woman's eggs are harvested and then fertilized with a man's sperm in the laboratory. The resulting embryos are then transferred into the uterus. In a study of 372 women undergoing IVF at a South Carolina hospital, researchers found that those who were underweight and overweight had lower pregnancy rates than normal-weight women. They observed women's body mass index (BMI), a measure of weight in relation to height used to gauge underweight and obesity while also taking into account known factors that affect IVF success, such as age and hormone levels. The researchers gave various doses of hormones to stimulate the ovaries and then transferred the embryos, usually about three at a time. Embryos were more likely to take hold in the uterus in normal-weight women than in underweight or overweight women. While normal-weight women became pregnant about half of the time, underweight and overweight women conceived about 35 percent of the time. Overall, underweight and overweight women were about half as likely to get pregnant as normal-weight women.

In very thin women, low levels of the chemical leptin, a natural regulator of body weight released by fat cells, may affect the discharge of eggs from the ovaries. In overweight women, one possibility is that 'metabolic derangements' or problems associated with obesity, such as high cholesterol, heart disease and diabetes, affect fertility. The researchers conclude that underweight and overweight women might suffer from hormonal imbalances or dysfunction during ovulation that could affect IVF. Women really need to pay attention to their body weight if they want to get pregnant. Underweight and overweight women can take steps to increase their chances of IVF success.

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