A woman expecting a baby may look down at her swelling belly with pride-but looking at her swelling thighs is usually a different matter. In a slimness-obsessed culture, the weight gain of a pregnancy can be a constant worry.

Some women are so upset by their changing bodies that they even try to limit normal, healthy weight gains. One study found 41 percent of women in childbirth classes had negative attitudes toward their weights. They agreed with statements such as "I am embarrassed at how big I have gotten during this pregnancy." The more a woman disliked her new pregnant shape, the less weight she gained.

Strenuous efforts to diet during pregnancy fly in the face of recommendations by the American College of Obstetrics and Gynecology (ACOG). The group suggests a weight gain of 27 - 35 pounds, although the group stresses that weight gain should not be rigidly restricted for most healthy women having normal pregnancies. Studies show that healthy middle-class women now gain an average of 33 pounds. I aim my patients at 25 pounds and no less and then they usually gain about 30 – 35. My patient population is generally not troubled by inadequate weight gain as were the people I think the ACOG recommendations apply to.

In the past, women were advised to limit their weight gain to 20 pounds or less. But studies in the 1960s found a direct relationship between pre-pregnancy weight, maternal weight gain and the baby's birth weight. Underweight mothers have underweight babies, and higher pregnancy gains increase the baby's chances of a normal birth weight.

The weight gains of pregnancy apparently have two functions. During the first four to five months, the mother's body lays down fat, preparing for the demands of late pregnancy, labor and nursing. That pregnancy fat tends to cluster in the buttocks and thighs-tough spots to reduce, as women battling "love handles" have found.

The weight gain of early pregnancy often persists in the face of nausea, when women eat less, not more. Pregnancy fatigue reduces physical activity, and the metabolism slows, so women burn fewer calories overall.

Nevertheless, some mothers are so nauseated that they fail to gain, or even lose slightly, in the early months, creating worries about their baby’s development. Although women who vomit during pregnancy do gain about three pounds less in the first 20 weeks than women who are not nauseated, nausea and vomiting are associated with lower rates of miscarriage, stillbirth, premature birth and low infant birth weight.