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Personal Health Jane Brody on health and aging.

Pregnancy, or the desire to become pregnant, often inspires women to take better care of themselves — quitting smoking, for example, or eating more nutritiously.

But now many women face an increasingly common problem: obesity, which affects 36 percent of women of childbearing age. In addition to hindering conception, obesity — defined as a body mass index above 30 — is linked to a host of difficulties during pregnancy, labor and delivery.

These range from gestational diabetes, hypertension and pre-eclampsia to miscarriage, premature birth, emergency cesarean delivery and stillbirth.

The infants of obese women are more likely to have congenital defects, and they are at greater risk of dying at or soon after birth. Babies who survive are more likely to develop hypertension and obesity as adults.

To be sure, most babies born to overweight and obese women are healthy. Yet a recently published analysis of 38 studies found that even modest increases in a woman’s pre-pregnancy weight raised the risks of fetal death, stillbirth and infant death.

Personal biases and concerns about professional liability lead some obstetricians to avoid obese patients. But Dr. Sigal Klipstein, chairwoman of the committee on ethics of the American College of Obstetricians and Gynecologists, says it is time for doctors to push aside prejudice and fear. They must take more positive steps to treat obese women who are pregnant or want to become pregnant.

Dr. Klipstein and her colleagues recently issued a report on ethical issues in caring for obese women. Obesity is commonly viewed as a personal failing that can be prevented or reversed through motivation and willpower. But the facts suggest otherwise.

Although some people manage to shed as much as 100 pounds and keep them off without surgery, many obese patients say they’ve tried everything, and nothing has worked. “Most obese women are not intentionally overeating or eating the wrong foods,” Dr. Klipstein said. “Obstetricians should address the problem, not abandon patients because they think they’re doing something wrong.”

Dr. Klipstein is a reproductive endocrinologist at InVia Fertility Specialists in Northbrook, Ill. In her experience, the women who manage to lose weight are usually highly motivated and use a commercial diet plan.

“But many fail even though they are very anxious to get pregnant and have a healthy pregnancy,” she said. “This is the new reality, and obstetricians have to be aware of that and know how to treat patients with weight issues.”

The committee report emphasizes that “obese patients should not be viewed differently from other patient populations that require additional care or who have increased risks of adverse medical outcomes.” Obese patients should be cared for “in a nonjudgmental manner,” it says, adding that it is unethical for doctors to refuse care within the scope of their expertise “solely because the patient is obese.”

Obstetricians should discuss the medical risks associated with obesity with their patients and “avoid blaming the patient for her increased weight,” the committee says. Any doctor who feels unable to provide effective care for an obese patient should seek a consultation or refer the woman to another doctor.

Obesity rates are highest among women “of lower socioeconomic status,” the report notes, and many obese women lack “access to healthy food choices and opportunities for regular exercise that would help them maintain a normal weight.”

Nonetheless, obese women who want to have a baby should not abandon all efforts to lose weight. Obstetricians who lack expertise in weight management can refer patients to dietitians who specialize in treating weight problems without relying on gimmicks or crash diets, which have their own health risks.

Weight loss is best attempted before a pregnancy. Last year, the college’s committee on obstetric practice advised obstetricians to “provide education about possible complications and encourage obese patients to undertake a weight-reduction program, including diet, exercise, and behavior modification, before attempting pregnancy.”

An obese woman who becomes pregnant should aim to gain less weight than would a normal-weight woman. The Institute of Medicine suggests a pregnancy weight gain of 15 to 25 pounds for overweight women and 11 to 20 pounds for obese women.

Although women should not try to lose weight during pregnancy, “a woman who weighs 300 pounds shouldn’t gain at all,” Dr. Klipstein said. “This is not harmful to the fetus.”

Dr. Klipstein also noted that obesity produces physiological changes that can affect pregnancy, starting with irregular ovulation that can result in infertility.

Obese women are more likely to have problems processing blood sugar, which raises the risk of birth defects and miscarriage. There is also a greater likelihood that their baby will be too large for a vaginal delivery, requiring a cesarean delivery that has its own risks involving anesthesia and surgery.

The babies of obese women are more likely to develop neural tube defects — spina bifida and anencephaly — and to suffer birth injuries like shoulder dystocia, which may occur when the infant is very large.

High blood pressure, more common in obesity, can result in pre-eclampsia during pregnancy, which can damage the mother’s kidneys and cause fetal complications like low birth weight, prematurity and stillbirth.

It is also harder to obtain reliable images on a sonogram when the woman is obese. This can delay detection of fetal or pregnancy abnormalities that require careful monitoring or medical intervention.