Of pregnancy and pounds: researchers weigh the value of plumping up expectant moms.

Of Pregnancy and Pounds

Pregnant women putting on more weight than expected shouldn't necessarily deny themselves that extra scoop of ice cream, a growing body of research suggests.

Despite a national preoccupation with staying in shape -- even while pregnant -- current U.S. guidelines that set limits for acceptable weight gains during pregnancy appear overly conservative, according to a new study of the relationship between maternal weight gain and pregnancy outcome. In addition, a new report by the Institute of Medicine, a part of the National Academy of Sciences in Washington, D.C., finds fault with current weight-gain "upper limits." Taken together, the two reports highlight a newly emerging U.S. pregnancy paradigm that accepts a wider range of prenatal plumpness.

No consensus exists in the United States on how many pounds a woman should gain during pregnancy. But of the various guidelines published by national scientific committees and medical organizations during the past 20 years, most have recommended a maximum of about 25 pounds; the most liberal published guidelines allowed gains of nearly 31 pounds.

The June Institute of Medicine report broke weight-watching ranks by sanctioning gains of up to 35 pounds in women with average prepregnancy weights. And research reported in the July OBSTETRICS AND GYNECOLOGY suggests that for some women, increases of 40 pounds or more may be acceptable. Although specific limits will vary from person to person, "a wider range of maternal weight gain than is currently recommended is associated with good pregnancy outcome," conclude Barbara Abrams, a nutritional epidemiologist at the University of California, Berkeley, and Jennifer D. Parker of the University of California, San Francisco (UCSF).

Abrams and Parker analyzed medical records of the 4,674 women at UCSF's Moffitt Hospital who, between 1980 and 1988, experienced "good pregnancy outcomes." These were pregnancies in which the mother had no diabetes or hypertension and vaginally delivered a single, healthy, normal-weight baby of 37 to 42 weeks' gestation.

Although prenatal weight gains varied widely among individual mothers -- depending largely upon race and pre-pregnancy body weight -- 75 percent of these healthy women gained more than the commonly recommended 26 pounds. The median weight gained -- the amount for which half of all the women gained more and half gained less -- was 33 pounds. All told, fully 80 percent of the women gained between 22 and 46 pounds, and about a quarter of those gained more than 40 pounds -- with no apparent problems for mother or child.

Historically in the United States, "weight restriction has been more popular than encouraging ample weight gain" during pregnancy, Abrams told SCIENCE NEWS from her home in Berkeley, where she is in the midst of her own postpartum recovery. (Abrams gained a very normal 27 pounds before delivering her 7-pound, 13-ounce son, Alexander.)

In the 1950s and '60s, she says, obstetricians believed that pregnancy-related weight gains of more than 15 pounds caused maternal hypertension, delivery complications and an increased risk of permanent, postpartum obesity -- assumptions for which no good evidence exists. With the recognition in the 1970s that extremely lean moms generally give birth to low-birthweight babies -- with neonatal health risks much more real than those supposed for overweight mothers -- recommendations began to change.

Reports by such groups as the National Research Council and the American College of Obstetricians and Gynecologists today encourage adequate fetal growth by providing recommended ranges for weight gains during pregnancy. But some obstetricians have criticized these ranges because only the average weight-gain values, and not the upper and lower limits, were derived from scientific data.

The new analysis by Abrams and Parker helps clarify those upper and lower limits. Their data indicate that currently assumed lower-limit gains of about 20 pounds are reasonable, but that popularly quoted upper limits of about 26 pounds are probably too low.

That conclusion is echoed in "Nutrition During Pregnancy," issued by the Institute of Medicine in June. The report recommends that women of average weight prior to pregnancy gain as much as 35 pounds, or just over the median weight that Abrams and Parker found associated with healthy deliveries.

Significantly, both reports make a point of breaking down their data according to a woman's weight prior to pregnancy. This signifies a growing recognition that initial weight serves as a major determinant of what constitutes an appropriate pregnancy gain. According to the Institute of Medicine report, for example, physicians may encourage underweight women to gain as much as 40 pounds, while overweight women should limit their increases to 25 pounds.

Abrams emphasizes that her study only correlates healthy outcomes with prenatal weight gains. Further studies--which she plans to perform--must clarify the links between specific weight gains and problem pregnancies. So, while it's true, for example, that 90 percent of her normal-weight, healthy-outcome mothers gained between 17.5 and 53 pounds during pregnancy, it remains unknown what percentage of all mothers gaining the extremes--17.5 or 53 pounds--experienced unhealthy outcomes.

Moreover, Abrams notes, scientists remain uncertain about the longer-term consequences of excessive weight gain in pregnant women. It's unlikely that health problems would occur in these women's children without some clue appearing soon after birth, she says. And most mothers end up retaining only about 2.2 of the "extra" pounds after each pregnancy, Abrams says, "which shouldn't really be a problem unless you have 20 kids." But both Abrams and the Institute of Medicine report note a need for other studies to elicit any relationship between weight gain during pregnancy and a woman's subsequent obesity, as well as any links between weight gains and complications of labor or delivery.

Most important, Abrams notes, "weight gain is only a partial predictor" of healthy pregnancy outcomes. "It's an indicator that suggests, but does not guarantee," a healthy outcome, she says.

"There are so many factors that contribute to a healthy pregnancy," Abrams concludes. She recommends a complete nutritional assessment and lifestyle analysis of such risk factors as smoking and consumption of alcohol for all pregnant women.