In this issue of Epidemiology Chen et al1 report that mothers who were obese entering pregnancy have infants with an elevated risk for mortality throughout the first year of life. Among the obese mothers, infant mortality was highest among those who gained the most weight during pregnancy. Very low rates of weight gain, particularly among underweight mothers, also increased risk for infant death. These findings, albeit from births that occurred 20 years ago, concord with results from more recent pregnancies and highlight the independent influences of weight before pregnancy and weight gain during pregnancy.
However, we know little about the pathways by which maternal obesity and weight gain result in infant deaths. We know even less about the extent to which we can intervene to change these risks. In 2005 the American College of Obstetrics and Gynecology issued their first-ever guidelines regarding management of obese obstetric patients,2 but it is not yet clear whether following these or any other management practices improves outcomes.
Both neonatal and infant mortality are, fortunately, rare occurrences in the United States, although not as low as in other developed countries.3 Other less extreme but more common outcomes related to excess maternal weight or weight gain (including gestational diabetes, preeclampsia, fetal macrosomia, instrumented delivery, and birth trauma) not only cause complications around the time of birth but also confer elevated chronic disease risk for both mother and child.4 Independent of their weight entering pregnancy; mothers who gain more weight during pregnancy are more likely to retain that weight after pregnancy; they are also more likely to have children at elevated risk for becoming overweight,5,6 perhaps fostering an intergenerational spiral of obesity.
Based on results from observational studies, there is good reason to believe that constraining gestational weight gain within an optimal range will minimize adverse outcomes, even among obese women. The first step will be to determine the optimal weight change. Whereas the relationship of gestational weight gain with infant mortality is U-shaped, it seems that gestational gain is directly associated with maternal postpartum weight retention and child overweight risk and inversely associated with risk for small-for-gestational-age birth. These relationships not only differ in strength and direction, but also in gravity. Studies are needed that simultaneously incorporate multiple short-and long-term outcomes.
Current recommendations do not provide a great deal of guidance regarding how much weight change is optimal among obese women. In 1990 the US Institute of Medicine (IOM) published gestational weight gain recommendations still in use today.7 The report was primarily concerned with reducing the risks of preterm delivery and restrained fetal growth resulting from insufficient weight gain. The IOM’s advice that obese women gain “at least 6 kg”—the approximate weight of the fetus, placenta, and decidual tissues—with no recommended ceiling, catches by surprise many of us now fully immersed in the obesity epidemic, and highlights the lack of data available 2 decades ago regarding outcomes of gestational weight gain among obese women. The shift in focus to the perils of too much weight gain may explain the apparently mistaken recommendation in the National Heart, Lung, and Blood Institute’s authoritative 1998 obesity guidelines,8 which cited a recommendation for gestational weight gain of “up to 6 kg.” In fact, recent studies have raised the possibility that among obese women, the optimal weight change during pregnancy to minimize adverse outcomes at birth may be weight loss.9,10
This year the IOM convened a new committee, whose recommendations are expected in 2009, to review recent evidence regarding influences of pregnancy weight on maternal and child health. This committee will be challenged not only to determine the ideal range of gestational gain considering short- and long-term outcomes for mother and child, but also to figure out how best to disseminate any revised recommendations. Only about a third of mothers now gain weight within current guidelines, and more than half of pregnant women are gaining more than recommended. Even within the more controlled setting of an intervention trial, many investigators have been unable to help women limit their gain within targeted ranges.11 Future intervention work will need to draw upon state-of-the-art behavior change strategies.
Helping women achieve a healthy weight before becoming pregnant poses an even greater challenge. Obesity particularly affects women, and now almost a third of young women are obese. In its recent guidelines for preconception care, the Centers for Disease Control and Prevention highlighted maternal obesity as a major factor related to adverse perinatal outcomes.12 Solving the obesity epidemic will take a coordinated effort across every level of society. Helping women gain an appropriate amount of weight during pregnancy will at least be a step in the right direction.
ABOUT THE AUTHOR
EMILY OKEN is an Assistant Professor in the Department of Ambulatory Care and Prevention at Harvard Medical School, and a primary care doctor at the Fish Center for Women’s Health at Brigham and Women’s Hospital. Her research focuses on how maternal diet, physical activity, and other behaviors in the peripartum period influence maternal and child health.
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2. American College of Obstetrics and Gynecology. ACOG committee opinion. Number 319, October 2005. The role of obstetrician-gynecologist in the assessment and management of obesity. Obstet Gynecol
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12. Centers for Disease Control and Prevention. Proceedings of the Preconception Health and Health Care Clinical, Public Health, and Consumer Workgroup Meetings. In: Kent H, Johnson K, Curtis M, et al, eds. Preconception Health and Health Care
. Atlanta, GA: Available at: http://www.cdc.gov/ncbddd/preconception/default.htm