New guidelines recommend pregnant women gain more weight, skip vitamins.

According to guidelines released June 6, 1990 by the Institute of Medicine in Washington, D.C., pregnant women who eat balanced diets do not need extra vitamins and can safely gain more weight than previously recommended.

The guidelines, based on a review of studies on nutrition, weight gain and pregnancy, said the average woman who gains 25 to 35 pounds during pregnancy is more apt to produce a healthy, normal-weight baby than one who gains less. And with the exception of iron, vitamins and other supplements are of no known value in pregnancy, the study said. Such supplements are routinely prescribed for pregnant women.

Lindsay Allen, a professor of nutrition at the University of Connecticut who was a chairwoman of a study subcommittee, said that when not told to restrict their diet during pregnancy, pregnant women normally gain 25 to 35 pounds.

"What we are doing is recognizing that dietary restriction in pregnancy is not a good idea," Ms. Allen said. "Normal weight gain is better."

Dr. Roy M. Pitkin, an obstetrician at the University of California, Los Angeles, who chaired the study committee said, "In a sense, This brings health recommendations in line with what is actually happening."

Weight gain in pregnancy has been a major issue since the 19th century, when physicians believed overeating led to large babies and difficult labors. In recent years, most doctors have followed guidelines established in 1970 by the National Research Council that advised women to gain no more than 25 pounds during pregnancy.

But Ms. Allen said the committee studied new data that show "women can gain more weight and have babies who are bigger and healthier at birth."

The report said a woman's weight gain should be evaluated during pregnancy, considering her height and body type.

How fast women gain is important. The committee said a gain of one pound a week is best during the second and third trimesters of pregnancy for the average woman, while overweight women should gain at half that rate.

"A smooth, steady weight gain usually is an indication of an increase in lean and fat [mass]," a committee statement said.

For normal women eating balanced diets, Ms. Allen said, vitamin pills and other food supplements are not needed and could even be hazardous. An exception is iron pills.

"Supplements of 30 milligrams of ferrous iron are recommended daily during the second and third trimesters," the study said.

But Ms. Allen said that even iron supplements should be used with caution since dosages above 30 milligrams interfere with the absorption of other essential nutrients. And Dr. Pitkin said iron pills during the first trimester could aggravate nausea.

As with weight gain, the use of supplements should be evaluated case by case, the committee said.

Ms. Allen said added nutrients might be appropriate for women who did not eat a balanced diet, or who were carrying more than one baby, or for women at higher risk because of tobacco, alcohol or drug abuse.

The study was organized by the National Research Council for the Institute of Medicine. Both organizations are affiliated with the National Academy of Sciences, a private organization chartered by Congress.