In this prospective study, we found that misperceived pre-pregnancy body weight status was directly associated with excessive gestational weight gain in both normal weight and overweight/obese women. Compared with normal weight women who accurately assessed their pre-pregnancy weight status, the odds of gaining excessively during pregnancy were increased seven-fold among overweight/obese women who underassessed their pre-pregnancy body weight status. Normal weight women who overassessed their pre-pregnancy weight status had twice the odds of excessive gestational weight gain.
Our findings parallel studies in non-pregnant women that have shown associations of misperception of weight status with nutritional habits or weight gain [23
]. To our knowledge, however, our paper is the first to report associations between weight status misperception and weight gain in pregnancy. Given both the harmful consequences and increasing prevalence of excessive gestational weight gain [1
], identifying potentially modifiable predictors is critical to the design of interventions to reduce weight gain and improve maternal and child health.
The weight misperception variable we used could represent body dissatisfaction, often defined as the discrepancy between current and ideal body size, which may affect persons of either normal or overweight/obese weight status. Normal weight women who overassess their weight status are at increased risk of developing eating disorders, such as anorexia, bulimia and binge eating disorder [24
]; these same disordered eating behaviors are directly related to body dissatisfaction [28
]. Dissatisfaction with body size may also contribute to misperception among overweight/obese women who attempt to attain the media's thin ideal [28
], promoting recurrent dieting, loss of restraint, binging, and weight gain [44
]. Data linking body dissatisfaction with weight gain in pregnancy, however, are limited and inconsistent. DiPietro et al [20
] reported a strong correlation between poor pregnancy body image and over-gain at 36 weeks' gestation, but more recent work has revealed an inverse relationship between body size dissatisfaction and gestational weight gain [45
]. In the postpartum period, Harris and colleagues [46
] found that mothers who felt more dissatisfied with their bodies immediately after pregnancy had significantly greater long term (> 2 year) weight gains than women who had no increase in dissatisfaction. More research is needed to clarify the relationships among weight status misperception, body dissatisfaction, and peripartum weight gain, given the potential for behavioral modification.
Alternatively, misperception of body weight status may signify a lack of awareness about the clinical thresholds of normal and overweight/obese. Among overweight and obese non-pregnant women, some investigators have speculated that a lack of awareness about overweight may be responsible for misperception, influenced in part by the high prevalence of the condition in the US [26
]. Given that over two-thirds of Americans are overweight or obese, social comparison among overweight women might affect their judgment about their respective weight status, particularly among Black and Hispanic women for whom a heavier body image is often most accepted [25
]. By failing to recognize their overweight/obese status, these women may be less likely to stay within the IOM guidelines for weight gain in pregnancy.
We speculate that a combination of biologic and behavioral mechanisms may explain the relationship between misperceived body weight and excessive gain. Recent work has implicated the prefrontal cortex, especially in the right hemisphere, as a critical area involved in the cognitive control of food intake and body size perception [46
]. Whether alterations in brain function exist in women who misperceive their weight status just prior to pregnancy has yet to be fully elucidated, but provides an interesting area for further investigation. Weight misperception may also influence behaviors, such as physical activity and dietary intake, that by themselves lead to weight gain [25
]. In our analysis, however, including dietary and activity behaviors in our models did not attenuate the relationship between misperception and excessive gain. It is unclear whether this is an issue of timing or accuracy with regard to dietary and activity assessment, or whether other behaviors not measured in our cohort, such as binge eating or dietary restraint, are the true behavioral mediators.
Also worth mentioning is our finding that overweight/obese women who accurately assess their weight status are at a 3-fold increased odds of gaining excessively during pregnancy. Correction of misperception among overweight/obese women at the start of pregnancy may therefore reduce, but not eliminate the potential for excessive gain. A better understanding of the reasons for excessive gain in these women is necessary (beyond body weight misperception), given the high proportion of overweight and obese women of childbearing age in the US.
Our study has a number of strengths including a relatively large sample size, prospective data collection, and inclusion of multiple confounding variables. However, several limitations to this study exist. Our cohort was highly educated, of higher income, and mostly white, which may limit generalizability of our results to more racially and economically diverse groups of women. In our sample, women had somewhat lower levels of misperception and overweight than have been reported elsewhere. Information about pre-pregnancy weight and weight perception was obtained via questionnaire at approximately 10 weeks' gestation and may be subject to recall bias. However, data published by Skouteris et al revealed that women "feel as fat" in early pregnancy as they did pre-pregnancy (the 3 month period prior to pregnancy), and thus weight perception is unlikely to differ substantially at the 2 timepoints [49
]. It is also possible that women who misperceive do not accurately report pre-pregnancy weight; however, in a study among high school students, the proportion of students who misperceived their body weight was approximately the same regardless of whether the BMI category was calculated from measured or self-reported height and weight [23
]. The weight perception and physical activity questions used here have not been validated in other pregnant populations. Diet and physical activity were measured in mid-pregnancy and may not reflect behavior in late pregnancy that could have a greater impact on gestational weight gain. As pre-pregnancy weight was self reported in our cohort, it is likely to be underestimated, and therefore gestational weight gain may be overestimated. However, our validation study indicated that ranking of individuals is preserved [9
]. Finally, although the time between last measured pregnancy weight and delivery varied by up to 4 weeks in our sample, our results remained unchanged after adjustment for this difference.