Over the past several decades, both actual and recommended gestational weight gains have increased in the US 12. Although higher maternal weight gain was initially thought to improve infant health and reduce perinatal mortality 13, more recent data have focused on the negative effects of gaining too much during pregnancy 4, including undesirable birth outcomes 5678, childhood overweight 9, and higher postpartum weight retention, which predisposes to later risk of obesity in the mother 1310. Given that approximately 40–50% of pregnant women gain more than recommended by current Institute of Medicine (IOM) guidelines 91112, there is a renewed interest in better understanding the determinants of excessive gain.

Identified risk factors for excessive gestational weight gain include higher pre-pregnancy weight 131415, primiparity 1416, lower income 17, insufficient knowledge of weight gain recommendations (and their importance) 13, recurrent pre-pregnancy dieting 1819, lack of health provider advice and negative attitudes about weight gain 132021, along with pregnancy-related behaviors such as lower levels of physical activity and increased food consumption 1722. However, the relationship of a woman's perception of her weight status with weight gain in pregnancy has not been elucidated.

Among non-pregnant adolescents and young adults, evidence suggests that body weight perception is an important correlate of nutritional habits and weight gain 2324252627. Adolescents who are underweight or normal weight but perceive themselves as overweight are at a two-fold increased risk of disordered eating behaviors, including binge eating disorder or bulimia 24, which by themselves have been shown to predict the development of inappropriate weight gain and obesity 282930. Young adults who are overweight or obese, but do not perceive themselves as such, are less likely to engage in physical activity and weight control behaviors 25. Without recognition of their overweight status, these individuals have been posited to ignore messages related to healthy diet and lifestyle change 2627.

To determine whether similar relationships exist in pregnancy, we used data from a longitudinal birth cohort study to examine the association of misperceived pre-pregnancy body weight status with excessive gestational weight gain. We hypothesized that women who underassessed or overassessed their pre-pregnancy weight status would be at increased risk of excessive gestational weight gain, compared to women who accurately assessed their pre-pregnancy weight status. In addition, we explored potential mechanisms by which misperceived body weight status may promote weight gain in pregnancy.

One thousand twenty-nine (67%) of the 1537 participants reported that they were normal weight just prior to pregnancy, of whom 898 (87%) accurately perceived their weight status and 131 (13%) overassessed their weight status. Of the remaining 508 (33%) women who were overweight/obese, 438 (86%) accurately perceived and 70 (14%) underassessed their pre-pregnancy weight status. Just under one-third of participants were non-white; a similar proportion had not graduated from college. Mean age was 32.3 years (standard deviation [SD] 4.9). Compared with normal weight women who accurately perceived their pre-pregnancy weight status, overweight/obese underassessors were younger, more likely to be non-white, of lower income, less educated, and single (Table 1). During pregnancy, overweight/obese underassessors consumed fewer fruits and vegetables, but did not differ from normal weight accurate assessors in amount of vigorous activity and fried food intake. Normal weight overassessors, on the other hand, were relatively similar in all characteristics to their accurate assessor counterparts (Table 1).

Participants gained a mean of 15.6 kg (range -7.3 to 40.9) in pregnancy (mean gestation length 39.5 weeks, SD 1.9), and 823 (54%) gained excessively according to Institute of Medicine criteria 4. Rates of excessive weight gain varied across exposure categories: 57% of normal weight overassessors, 62% of overweight/obese accurate assessors, and 81% of overweight/obese underassessors had excessive gestational weight gain, while only 47% of normal weight accurate assessors gained excessively (p < 0.05 for all comparisons to normal weight accurate assessors, Figure 1).

On multivariable analyses, after adjustment for maternal sociodemographics, pre-pregnancy BMI, gestation length, parity and smoking habits, misperception of pre-pregnancy body weight status was associated with an increased odds of excessive gestational weight gain (normal weight overassessors, OR: 2.0, 95% CI: 1.3, 3.0; overweight/obese underassessors, OR: 7.6, 95% CI: 3.4, 17.0; Table 2). In addition, overweight/obese women who accurately perceived their body weight status had an almost 3-fold increased odds of excessive gestational weight gain compared to their normal weight counterparts. When we restricted our sample to include only the 1427 women who delivered at term (> = 37 weeks gestation), we did not observe a marked difference in the magnitude of our results (normal weight overassessors, OR: 2.1, 95% CI: 1.4, 3.1; overweight/obese accurate assessors, OR: 2.9, 95% CI: 2.2, 4.0; overweight/obese underassessors, OR: 7.8, 95% CI: 3.4, 18.0). There was no modification of the effect of weight misperception by race/ethnicity, parity, or income (all p values for interaction terms > 0.20).

We next studied maternal behaviors that might serve as intermediates in the pathway between weight misperception and excessive gestational weight gain. Inclusion into the multivariable model of the behaviors (vigorous activity, consumption of fried food away from home, fruit and vegetable intake, and consumption of a vegetarian diet) did not substantially alter observed associations of weight misperception with excessive gestational weight gain (OR adjusted for all factors listed previously: normal weight overassessors, OR: 2.1, 95% CI: 1.3, 3.2; overweight/obese underassessors, OR: 8.0, 95% CI: 3.2, 20.0). Therefore, we did not have evidence that these factors mediated the relationship between misperceived pre-pregnancy body weight status and excessive gestational weight gain.

Since ORs are poor estimates of relative risks when the outcome is highly prevalent, as is the case for excessive gestational weight gain, we also calculated the predicted prevalence of excessive gestational weight gain by exposure categories, using parameters in our final multivariable model. We present examples of these results in Table 2. Rates of excessive gestational weight gain exceeded 50% in all but normal weight accurate assessors, over a range of maternal sociodemographic characteristics. Comparing overweight/obese underassessors with normal weight accurate assessors, the predicted probability of excessive gestational weight gain ranged from 1.8 to 2.2. Thus, the OR of 7.6, while accurate and unbiased, overestimates the risk ratio, which is about 2.

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 2324252627. 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 134567891012, 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 2441; these same disordered eating behaviors are directly related to body dissatisfaction 2842. Dissatisfaction with body size may also contribute to misperception among overweight/obese women who attempt to attain the media's thin ideal 2843, 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 252647. 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 2526. 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.

In summary, we found that misperceived pre-pregnancy body weight status was associated with excessive gestational weight gain. Once the etiology of the misperception variable is better understood, future interventions should test the potential benefits of correcting misperception in order to reduce the risk of excessive gestational weight gain. As women are particularly receptive to behavior change recommendations during pregnancy 50, interventions such as these may be effective in promoting long-term health among childbearing women and their children.

The authors declare that they have no competing interests.

SJH conceived of the study and participated in data interpretation and manuscript writing, under the supervision of MWG. EO, JH, and JWR contributed to the design of the study and manuscript preparation. SLR completed the analyses. KPK provided statistical support and help in interpreting findings. All authors read and approved the final manuscript.