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NEW YORK (Reuters Health) - Obese women who lose weight during pregnancy may have a lower risk of certain pregnancy complications, but -- with the exception of extremely obese women -- those benefits may be outweighed by negative effects on the baby's birth size, a new study suggests.
The findings, published in the obstetrics journal BJOG, add to the fairly controversial idea that it can be healthy for obese pregnant women to maintain their pre-pregnancy weight, or even lose a few pounds.
Currently, the Institute of Medicine (IOM), an advisory body to the U.S. government, recommends that normal-weight women gain between 25 and 35 pounds during pregnancy. Underweight women are advised to gain 28 to 40 pounds, while those who are overweight should put on 15 to 25 pounds.
Obese women are given the narrowest weight-gain range, with 11 to 20 pounds considered optimal.
Obese women are at elevated risk of pregnancy complications like gestational (pregnancy-related) diabetes; pre-eclampsia, a potentially dangerous disorder marked by a sudden increase in blood pressure and protein in the urine; emergency cesarean section; and having a larger-than-normal baby.
Some studies have suggested that obese women can safely gain less than the recommended amount of weight, or possibly even lose weight, and lower their risk of such complications.
For the new study, researchers led by Dr. Andreas Beyerlein, of Ludwig-Maximilians University of Munich in Germany, reviewed the records of more than 700,000 women who delivered a baby between 2000 and 2007.
The women were divided into pre-pregnancy weight categories according to body mass index (BMI), a measure of weight in relation to height. Women with a BMI of 30 to 34.9 fell into the category of class 1 obesity; those with a BMI between 35 and 39.9 had class 2 obesity; and those whose BMI stood at 40 or above -- weighing some 100 pounds above their ideal body weight -- fell into the class 3 category, often referred to as morbid obesity.
Overall, those women who shed pounds generally had lower risks of emergency C-section and pre-eclampsia than obese women who gained weight during pregnancy. They were also less likely to have a larger-than-normal baby.
Among women with class 3 obesity, for example, 10 percent of those who gained weight developed pre-eclampsia. That compared with a rate of seven percent among those who lost weight during pregnancy.
When Beyerlein's team accounted for a number of other factors -- including the mother's age and smoking habits -- weight loss was associated with a 36 percent lower risk of pre-eclampsia among women with class 3 obesity. A similar reduction was seen among those in the class 2 category.
Meanwhile, women with class 1 or class 3 obesity had lower risks of emergency C-section if they lost weight. Of women in the former group, for example, 13 percent of those who gained weight ended up needing an unplanned C-section, versus just under nine percent of those who lost weight during pregnancy; the weight loss itself was linked to a 35 percent reduction in C-section risk.
However, among women with class 1 or 2 obesity, weight loss was also tied to an increased risk of having a smaller-than-normal baby.
In the class 1 group, for example, 13 percent of those who lost weight had a small newborn, compared with eight percent of those who gained weight. The same risk was not seen among the most severely obese women.
Exactly what should be made of the findings is not yet clear.
The study had a number of limitations. Since it was a retrospective study based on women's medical records, it can only show associations between weight changes and the odds of pregnancy complications -- and cannot prove cause-and-effect.
So it is difficult to translate the results into guidelines for women, Beyerlein told Reuters Health in an email. That said, the researcher added, the findings do suggest that, with the possible exception of women with class 3 obesity, most women should not lose weight during pregnancy, due to the potential effects on fetal growth.
A researcher not involved in the study said he disagreed with that interpretation.
Dr. Raul Artal, an obstetrician at Saint Louis University in Missouri who has studied the question of weight loss in obese pregnant women, said the findings do not mean that more-moderately obese women cannot safely shed pounds.
In an interview, he noted that the researchers did not have information on certain health factors -- like the presence of chronic high blood pressure -- that can affect a woman's odds of having a smaller-than-normal newborn.
The inability to account for such variables makes it more difficult to conclude that weight loss, per se, was responsible for the higher risk.
In a small 2007 study, Artal and his colleagues followed 96 obese pregnant women with gestational diabetes who either self-enrolled in a diet-and-exercise program designed to help them control their weight gain, or followed the diet typically prescribed to women with gestational diabetes.
The researchers found that women in either group who maintained or lost weight were less likely to have a larger-than-normal newborn. And there was no evidence that weight loss harmed fetal growth.
Artal, who was also the lead author on the American College of Obstetricians and Gynecologists current guidelines on exercise during pregnancy, contended that obese women "can safely maintain or even lose weight, under close medical supervision."
Artal has been critical of the IOM recommendations that obese women gain 11 to 20 pounds during pregnancy, arguing that such weight gain not only raises the odds of pregnancy complications like pre-eclampsia, but also contributes to women's lifetime weight problems and the associated health risks. Obese women commonly retain excess fat that they gain with each pregnancy.
In an article published earlier this year in the journal Obstetrics & Gynecology, Artal and colleagues at Yale University and Duke University also criticized the IOM guidelines for not considering the different classes of obesity when advising pregnant women on weight gain.
So with the messages on weight gain differing, what should obese pregnant women do?
Artal said his general advice is for women to eat a "nutrient-rich" diet -- which would include plenty of fruits, vegetables, legumes and high-fiber grains -- and to aim to take a 30-minute walk everyday as a form of low-impact physical activity.
He also advised all obese pregnant women to manage their weight only under the guidance of their obstetrician -- if possible, one with experience in managing high-risk pregnancies.
SOURCE: link.reuters.com/sew85q BJOG, online November 4, 2010.