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Effects of Obesity on Fertility and Pregnancy

Obese women have more infertility and are less successful at conceiving than women of normal weight. Once pregnant, obese women are more likely to have complicated pregnancies and are less likely to have a live born baby because of a higher rate of miscarriage, ectopic pregnancy and stillbirth. The babies born to obese women are more likely to die in the first month of life.

It is clear that women who are obese are at increased risk for infertility and other reproductive problems. Numerous studies have demonstrated that women who are obese (body mass index over 30) are more likely to have ovulation problems that result in irregular or infrequent menstrual cycles and infertility. Women who are obese are also at increased risk for miscarriage though the reasons for this are as yet unclear. In the treatment of infertility, they are less successful. For example, in vitro fertilization (IVF) pregnancy rates are lower in obese women compared to those of normal weight. This may be due in part to the fact that obese women do not respond to fertility medications as well and have a higher percentage of immature eggs. Fertility surgery is also riskier in obese women compared to normal weight women.

In a recent study presented at the American Society for Reproductive Medicine meeting, overweight women were 50% more likely to have an ectopic pregnancy (a pregnancy outside of the uterus, usually in the fallopian tube).

Obesity is a significant risk factor in adverse pregnancy outcomes. A recent study from Sweden compared obese women (those with a body mass index of greater than 35) to normal weight women (those with a BMI less than 26). Even after controlling for other factors that are known to increase the risk for adverse outcomes, the obese women had a much greater likelihood of these problems.

  • Pre-eclampsia, a problem with elevated blood pressure in pregnancy, was four to five times more likely to occur in the pregnancies of obese women.
  • Stillbirth was two to three times more likely to occur in the pregnancies of obese women.
  • During labor and delivery, there is a serious problem called shoulder dystocia which occurs when the shoulder of the baby gets caught in the mother’s pelvis. It is considered a medical emergency and can result in death or injury to the baby. Shoulder dystocia occurs during the deliveries of obese women two to three times more often.

Babies experience distress during labor two to thee times more often in the pregnancies of obese women. As a result of the problems during delivery, obese women are delivered by cesarean section two to three times more often than women of normal weight.

Finally, the Swedish study found that death of the babies born to obese women are two to four times more likely to die in the first 28 days of life (neonatal death). Other studies have also identified a higher risk of gestational diabetes in the pregnancies of obese women.