A woman’s body image can be tricky. Like a reflection in a funhouse mirror, a woman’s perception of her body might make her see herself thinner or more obese than she actually is. Researchers led by Temple University’s Sharon Herring, M.D., M.P.H., have found that this misperception is associated with excess weight gain during pregnancy — which can cause complications for both mother and baby.

In a study published on Dec. 19 in the journal BMC Pregnancy and Childbirth, Herring and a team of researchers from the department of ambulatory care and prevention at Harvard Medical School and Harvard Pilgrim Health Care found that overweight and obese women who thought they weighed less than they actually did at the start of pregnancy had seven times the odds of gaining excessive weight during their pregnancy. In contrast, normal weight women who thought they weighed more than they actually did had twice the odds of gaining excessive weight during their pregnancy.

The reasons for misperceived body weight aren’t clear, but Herring and her team speculate that the high prevalence of obesity in the United States might lead overweight woman to believe they are at a normal weight, and thus make them less likely to follow pregnancy weight gain guidelines.

In normal weight women, the researchers speculate that the misperception may represent body dissatisfaction and a predisposition to disordered eating behaviors such as binge eating or bulimia, which could result in excessive gain.

“But it isn’t clear yet whether these are the explanations,” said Herring, an assistant professor of medicine and public health at Temple University’s Center for Obesity Research and Education. “More work needs to be done to understand perceptions of weight among mothers at the start of pregnancy, and to determine if correcting misperception reduces the likelihood of excessive pregnancy weight gain.”

The Institute of Medicine recommends that normal weight women gain 25-35 pounds during pregnancy, and overweight or obese women gain 15-25 pounds. Over 50 percent of mothers in Herring’s study gained weight in excess of these guidelines, which can lead to higher rates of Caesarean sections, larger babies, and greater difficulty in losing weight after delivery, Herring says.

The study included more than 1,500 women enrolled in the Project Viva birth cohort who were normal weight, overweight or obese at the beginning of their pregnancies. Among normal weight women, 13 percent thought they were heavier than they truly were, while 14 percent of the overweight or obese group thought they were lighter than they really were. The remaining participants in each group all accurately assessed their weight status.

Overweight or obese mothers who underestimated their weight status tended to be younger, non-white, of lower income, less educated and single and ate fewer fruits and vegetables than those in the normal weight group who accurately reported their weight. Normal weight women who underestimated their weight status, however, shared relatively similar characteristics to their accurate assessing counterparts.

While some of the mothers who accurately assessed their weight also gained excessive pounds, those who misperceived their weight were at greater risk of excessive gain.

Other authors on this study include Emily Oken M.D., M.P.H., Jess Haines, Ph.D., M.H.Sc., R.D., Sheryl L. Rifas-Shiman, M.P.H., Ken P. Kleinman, Sc.D., and Matthew Gillman, M.D., S.M., of Harvard Medical School and Harvard Pilgrim Health Care; and Janet Rich-Edwards of Brigham and Women’s Hospital in Boston. This research was funded by grants from the National Institutes of Health (NIH), Harvard Medical School and the Harvard Pilgrim Health Care Foundation. Herring was additionally supported by an Institutional National Research Service Award from the NIH.

Founded March 1, 2006, the Center for Obesity Research and Education (CORE) is a universitywide group of investigators dedicated to excellence in obesity research. Its mission is to facilitate interdisciplinary study of the etiology, consequences, treatment and prevention of obesity. CORE contains approximately 11,000 square feet of clinical research space, three conference rooms equipped with chairs to accommodate larger individuals, and three exam rooms where height, weight, blood pressure, and waist circumference can be measured. Ongoing research ranges from basic science to epidemiology, with a particular focus on the causes, treatment and prevention of obesity among minorities of lower socioeconomic status, with whom obesity is more prevalent.