When it's not just baby weight

In a study published on December 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 to 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 US might account for a skewed body image among the overweight or obese group so that they believe they are at a normal weight, and may be less likely to follow pregnancy weight gain guidelines as a result.

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 in excess of these recommendations, which Herring says can lead to higher rates of Caesarean sections, larger babies, and greater difficulty in losing weight after delivery.

The study looked at more than 1,500 women enrolled in Project Viva, a US 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 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 an excessive amount, those who misperceived their weight were at greater risk of excessive gain.

Source: Temple University