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Keywords:

  • population studies;
  • women's health;
  • pregnancy;
  • prevalence

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Objective: Pre-pregnancy obesity poses risks to both pregnant women and their infants. This study used a large population-based data source to examine trends, from 1993 through 2003, in the prevalence of pre-pregnancy obesity among women who delivered live infants.

Research Methods and Procedures: Data from the Pregnancy Risk Assessment Monitoring System in nine states were analyzed for trends in pre-pregnancy obesity (BMI > 29.0 kg/m2) overall and by maternal demographic and behavioral characteristics. Pre-pregnancy BMI was calculated from self-reported weight and height on questionnaires administered after delivery, and demographic characteristics were taken from linked birth certificates. The sample of 66,221 births was weighted to adjust for survey design, non-coverage, and non-response, and it is representative of all women delivering a live birth in each particular state. The sampled births represented 18.5% of all births in the United States.

Results: Pre-pregnancy obesity increased 69.3% during the study period, from 13.0% in 1993 to 1994 to 22.0% in 2002 to 2003. The percentage increase ranged from 45% to 105% for individual states. Subgroups of women with the highest prevalence of obesity in 2002 to 2003 were those who were 20 to 29 years of age, black, had three or more children, had a high school education, enrolled in Women, Infants, and Children, or were non-smokers. However, all subgroups of women examined experienced at least a 43% increase in pre-pregnancy obesity over this time period.

Discussion: The prevalence of pre-pregnancy obesity is increasing among women in these nine states, and this trend has important implications for all stages of reproductive health care.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Maternal obesity during pregnancy is associated with many complications such as cesarean delivery, macrosomia, gestational hypertension, preeclampsia, gestational diabetes, and fetal death (1, 2, 3, 4, 5, 6). Maternal obesity also increases the long-term risks for the fetus. Children born to obese mothers are twice as likely to be obese and to develop type 2 diabetes later in life (7, 8). Moreover, the prevalence of obesity is increasing among women in the United States. According to data collected for the National Health and Nutrition Examination Survey, obesity among women 20 to 39 years of age increased 33% in the interval between 1988 to 1994 and 1999 to 2000, from 21% to 28% of women in this age group (9). Among pregnant women, two population-based studies examined trends in pre-pregnancy BMI and found that overweight and obesity increased 40% in Utah between 1991 and 2001 and 9.2% in eight counties in upstate New York between 1999 and 2003 (10, 11). However, to date, there have been no national, regional, or multi-state population-based studies of pre-pregnancy BMI trends. To explore trends in a larger U.S. population, we examined pre-pregnancy obesity prevalence among women who delivered live-born infants in nine states over an 11-year period. In addition, we identified subgroups of women who experienced the greatest increases in pregnancy obesity and examined characteristics of women most at risk for obesity in 2002 to 2003.

Research Methods and Procedures

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Study Population

We analyzed data from the Pregnancy Risk Assessment Monitoring System (PRAMS),1 an ongoing population-based surveillance system that collects information in participating states on maternal behaviors associated with pregnancy. Each month, a stratified systematic sample of 100 to 200 mothers, who are state residents and have delivered a live-born infant in the preceding 2 to 4 months, is selected from birth certificate records. A self-administered, 14-page questionnaire is mailed to each mother. If the mother fails to respond, a second or third questionnaire is mailed to her. If there is no response to the repeat questionnaire, attempts are made to reach the mother for a telephone interview. Each mother's questionnaire is linked to her child's birth certificate. Data are weighted to adjust for survey design, non-coverage, and non-response. Currently, 29 states and New York City participate in collecting PRAMS surveillance data.

We selected states that had an annual response rate of 70% or higher and had data available for 1993 to 1994, 1998, and 2002 to 2003. The sample included 73,115 women who were surveyed in 1993 to 1994, 1998, and 2002 to 2003 in nine states [Alabama, Alaska, Florida, Maine, New York (excluding New York City), Oklahoma, South Carolina, Washington (data not available for 1993), and West Virginia]. Women with missing information on pre-pregnancy BMI (n = 6894, 9.4%, a total of 5.4% from 1993 to 1994, 2% from 1998, and 2% from 2002 to 2003) were excluded, leaving 66,221 women available for the analysis. The PRAMS protocol was approved by the Centers for Disease Control and Prevention Institutional Review Board, and the analysis plan was approved in the participating states.

Pre-pregnancy BMI was calculated from self-reported height and weight on the PRAMS questionnaire. In the analysis, we categorized women according to pregnancy-specific definitions put forth by the Institute of Medicine, which classifies pre-pregnancy BMI as underweight (<19.8 kg/m2), normal-weight (19.8 to 26.0 kg/m2), overweight (26.1 to 29.0 kg/m2), or obese (>29.0 kg/m2). We explored the prevalence of obesity by various characteristics of the mother. Race was based on self-report and categorized as white, black, or other (Alaska natives, American Indians, Asian Americans, and other). We were unable to examine trends in obesity for Hispanic women because PRAMS did not include the ethnicity variable from the birth certificate for 1993 and 1994. Age, race, education, marital status, and parity were obtained from the birth certificates, and Women, Infants, and Children (WIC) enrollment was obtained from the PRAMS questionnaire. Women who indicated that they were a smoker during pregnancy on either the birth certificate or the PRAMS were classified as smokers.

Analysis

We assessed the overall trend in obesity by combining BMI data for all nine states and conducting a χ2 test for trend using data from three time periods: 1993 to 1994, 1998, and 2002 to 2003. We used logistic regression to explore the relative contribution of time to obesity trends and direct standardization to assess the effect of changing population demographics. We constructed our multiple variable logistic regression model using obesity as the outcome and time as the primary exposure variable. In this model, we adjusted for maternal age, race, education, WIC enrollment, parity, and smoking status. Because obesity is common and odds ratios tend to overestimate the risk for common outcomes, we converted the adjusted odds ratio and 95% confidence interval to an adjusted relative risk using the method developed by Greenland (12). For direct standardization, the prevalence of obesity was directly standardized to the combined 1993 to 1994 and 2002 to 2003 distributions for maternal age, race, education, WIC enrollment, parity, and smoking status.

We also assessed trends in pre-pregnancy obesity by state and by maternal characteristics using a χ2 test for trend using data from 1993 to 1994 and 2002 to 2003. Maternal characteristics associated with obesity during the most recent time period (2002 to 2003) were identified using multiple variable logistic regression comparing women with pre-pregnancy obesity to women who had underweight or normal BMIs and converting the resultant odds ratios to relative risks.

For all analyses, the data were weighted to adjust for survey design, non-coverage, and non-response and, therefore, represent all women delivering a live birth in each respective state. SUDAAN was used to calculate the standard error, and the analysis reflected selection and response probabilities for the survey design (13).

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Generally, across all three time periods, women in our study population were most likely to be between the ages of 20 and 29 years, white, parous, not enrolled in WIC, and non-smokers during pregnancy, and to have more than a high school education (Table 1). Over the study period, the demographic distribution of women with live births changed. Compared with 1993 to 1994, women delivering in 2002 to 2003 were older, more likely to be of other race, more likely to have higher parity, less likely to be enrolled in WIC, and less likely to smoke during pregnancy.

Table 1.  Maternal characteristics by year, 1993–1994, 1998, and 2002–2003
Maternal characteristic1993 to 199419982002 to 2003p
  1. WIC, Women, Infants, and Children. Values are percent (standard error).

Age (yrs)   <0.0001
 <2013.5 (0.4)12.5 (0.3)10.9 (0.2) 
 20 to 2954.0 (0.6)52.1 (0.8)51.9 (0.5) 
 ≥3032.6 (0.5)35.4 (0.7)37.1 (0.5) 
Race   <0.0001
 White77.4 (0.3)77.1 (0.5)76.4 (0.3) 
 Black18.7 (0.3)17.8 (0.4)16.7 (0.3) 
 Other3.9 (0.2)5.1 (0.3)7.0 (0.2) 
Education (yrs)   <0.0001
 <1220.5 (0.5)18.8 (0.6)19.0 (0.4) 
 1236.8 (0.6)35.5 (0.7)32.5 (0.5) 
 ≥1342.7 (0.6)45.7 (0.8)48.5 (0.5) 
WIC enrollment   <0.005
 Yes43.0 (0.6)45.6 (0.7)45.1 (0.5) 
 No57.0 (0.6)54.4 (0.7)54.9 (0.5) 
Parity   <0.04
 043.7 (0.6)41.8 (0.8)42.5 (0.5) 
 1 to 248.0 (0.6)49.7 (0.8)48.2 (0.6) 
 ≥38.2 (0.3)8.5 (0.4)9.3 (0.3) 
Smoking during pregnancy   <0.0001
 Yes19.7 (0.5)16.9 (0.6)15.5 (0.4) 
 No80.3 (0.5)83.1 (0.6)84.5 (0.4) 

Overall, the prevalence of pre-pregnancy obesity increased 69.3%, from 13.0% in 1993 to 1994 to 22.0% in 2002 to 2003 (p < 0.001; Figure 1). After standardization for maternal age, race, education, WIC enrollment, parity, and smoking status, the estimated increase in prevalence of pre-pregnancy obesity changed slightly to 64.9%, from 13.4% in 1993 to 1994 to 22.1% in 2002 to 2003. Women delivering in 2002 to 2003 had a 70% (adjusted relative risk = 1.70; 95% confidence interval: 1.57, 1.85) increased risk of pre-pregnancy obesity compared with women in 1993 to 1994, after adjustment for maternal age, race, education, WIC enrollment, parity, and smoking status.

image

Figure 1. Percent of women with pre-pregnancy BMI > 29 kg/m2 by three time periods: 1993–1994, 1998, and 2002–2003.

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Prevalence of pre-pregnancy obesity increased in all states (Table 2). The percentage change was lowest in Oklahoma (45.3%) and highest in Maine (104.7%). The prevalence of pre-pregnancy obesity in 2002 to 2003 was lowest in Washington (18.4 ± 1.02%) and highest in West Virginia (25.98 ± 1.11%).

Table 2.  Prepregnancy BMI by state, 1993–1994, 1998, and 2002–2003
 1993 to 1994*1998*2002 to 2003* 
StateLeanNormalOverweightObeseLeanNormalOverweightObeseLeanNormalOverweightObese1993 vs. 2003 obesity (% change)
  • Values are percent (standard error). Lean, <19.8 kg/m2; normal, 19.8 to 26.0 kg/m2; overweight, 26.1 to 29.0 kg/m2; obese, >29 kg/m2.

  • *

    Difference significant across time for all states (p < 0.000).

  • Excludes New York City.

  • Does not include data for 1993.

Alabama20.8 (0.93)53.2 (1.16)10.4 (10.7)15.6 (0.9)19.0 (1.3)48.6 (1.7)11.0 (1.0)21.5 (1.4)14.7 (0.8)47.3 (1.2)12.9 (0.4)25.1 (1.0)60.6
Alaska14.4 (0.8)61.6 (1.11)9.9 (0.7)14.0 (0.8)12.9 (1.1)57.3 (1.6)11.9 (1.0)17.9 (1.2)9.9 (0.6)52.8 (1.0)14.8 (0.7)22.6 (0.9)60.6
Florida21.8 (1.0)56.3 (1.2)10.3 (0.7)11.6 (0.7)16.3 (1.3)57.5 (1.7)11.0 (1.1)15.2 (1.2)15.1 (0.9)51.4 (1.2)11.6 (0.8)22.0 (1.0)89.3
Maine18.9 (1.1)61.2 (1.3)8.8 (0.8)11.2 (0.9)13.5 (1.1)54.4 (1.7)10.3 (1.0)21.9 (1.4)13.2 (0.8)52.2 (1.2)11.8 (0.8)22.8 (1.0)104.7
New York17.2 (1.2)59.7 (1.7)10.4 (1.1)12.7 (1.2)13.5 (1.3)61.4 (1.9)11.8 (1.3)13.3 (1.4)14.4 (1.0)53.4 (1.3)11.1 (0.8)21.2 (1.1)66.8
Oklahoma21.6 (1.3)55.0 (1.5)9.6 (0.9)13.8 (1.0)17.8 (1.5)51.3 (1.9)13.5 (1.3)17.5 (1.4)16.2 (1.0)49.7 (1.3)14.0 (1.0)20.0 (1.0)45.3
South Carolina21.1 (1.0)52.9 (1.2)11.1 (0.7)14.9 (0.8)17.7 (1.6)52.8 (2.2)10.6 (1.4)18.9 (1.7)14.8 (1.1)46.0 (1.5)13.4 (1.2)25.8 (1.3)73.6
Washington19.1 (1.6)60.5 (2.0)8.7 (1.1)11.8 (1.3)15.4 (1.3)53.8 (1.8)12.8 (1.2)18.0 (1.4)14.8 (1.0)54.7 (1.3)12.1 (0.9)18.4 (1.0)56.3
West Virginia23.1 (1.1)51.7 (1.3)8.9 (0.7)16.3 (1.0)17.0 (1.3)47.8 (1.8)12.2 (1.2)23.1 (1.6)16.4 (0.9)45.8 (1.2)11.7 (0.8)26.0 (1.1)59.7
Overall20.1 (0.5)56.7 (0.6)10.2 (0.4)13.0 (0.4)16.0 (0.6)55.7 (0.8)11.6 (0.5)16.7 (0.6)14.8 (0.4)51.1 (0.6)12.1 (0.4)22.0 (25.1)69.3

When examining the prevalence of pre-pregnancy obesity by maternal characteristics, we found that it increased across all levels of age, race, education, WIC enrollment, parity, and smoking status; no subgroup of women experienced less than a 43% increase in pre-pregnancy obesity (Table 3).

Table 3.  Prepregnancy BMI by maternal characteristics, 1993–1994, 1998, and 2002–2003
 1993 to 1994*1998*2002 to 2003* 
Maternal characteristicLeanNormalOverweightObeseLeanNormalOverweightObeseLeanNormalOverweightObese1993 vs. 2003 obesity (% change)
  • WIC, Women, Infants, and Children. Values are percent (standard error). Lean, <19.8 kg/m2; normal, 19.8 to 26.0 kg/m2; overweight, 26.1 to 29.0 kg/m2; obese, >29 kg/m2.

  • *

    Difference significant across time for all covariates (p < 0.01) except for smoking status (p = 0.13).

Age (yrs)             
 <2032.0 (1.5)51.7 (1.7)9.1 (1.0)7.2 (0.8)27.1 (1.4)52.7 (1.7)10.7 (1.1)9.5 (1.0)25.2 (1.2)51.2 (1.4)9.4 (0.8)14.2 (1.0)97.0
 20 to 2920.0 (0.7)55.7 (0.8)10.5 (0.5)13.9 (0.6)15.4 (0.8)53.9 (1.1)12.0 (0.8)18.8 (0.8)15.4 (0.6)49.3 (0.8)11.8 (0.5)23.5 (0.7)69.7
 ≥3015.6 (0.9)60.8 (1.2)10.2 (0.7)13.5 (0.8)13.0 (1.0)59.3 (1.5)11.4 (0.9)16.3 (1.1)11.1 (0.7)53.6 (1.0)13.2 (0.7)22.1 (0.8)63.7
Race             
 White20.7 (0.6)58.3 (0.7)9.6 (0.4)11.4 (0.5)16.5 (0.7)57.1 (0.9)11.1 (0.6)15.3 (0.7)15.5 (0.5)52.3 (0.7)11.7 (0.4)20.5 (0.5)80.1
 Black15.7 (0.9)50.6 (1.3)13.2 (0.9)20.6 (1.1)11.4 (0.9)49.5 (1.7)14.3 (1.2)24.7 (1.5)9.8 (0.7)44.2 (1.1)14.5 (0.8)31.5 (1.0)52.9
 Other26.0 (2.7)57.2 (2.8)9.4 (1.7)7.4 (0.9)23.2 (2.6)55.8 (3.0)10.5 (2.1)10.6 (1.3)20.0 (1.6)54.6 (1.8)10.1 (1.0)15.3 (1.2)106.2
Education (yrs)             
 <1226.3 (1.3)50.5 (1.5)10.4 (0.9)12.8 (1.0)20.9 (1.4)50.4 (1.9)11.1 (1.2)17.6 (1.4)20.5 (1.1)48.1 (1.3)10.8 (0.8)20.6 (1.1)60.9
 1219.3 (0.8)54.5 (1.0)11.3 (0.7)14.9 (0.7)14.8 (0.9)52.5 (1.4)13.5 (1.0)19.3 (1.0)14.5 (0.7)47.2 (1.0)12.5 (0.6)25.8 (0.9)73.2
 ≥1318.1 (0.7)61.5 (0.9)9.2 (0.5)11.2 (0.6)15.1 (0.9)60.2 (1.2)10.6 (0.7)14.1 (0.8)12.8 (0.6)54.7 (0.8)12.3 (0.5)20.2 (0.6)80.1
WIC enrollment             
 Yes22.3 (0.8)50.8 (0.9)11.2 (0.6)15.7 (0.7)16.8 (0.8)50.6 (1.2)11.7 (0.8)20.9 (0.9)15.8 (0.6)45.5 (0.8)12.3 (0.5)26.4 (0.7)68.1
 No18.5 (0.6)61.2 (0.8)9.5 (0.5)10.8 (0.5)15.1 (0.8)59.7 (1.1)11.6 (0.7)13.6 (0.7)14.0 (0.6)55.5 (0.8)11.9 (0.5)18.6 (0.6)72.5
Parity             
 023.3 (0.8)57.3 (0.9)9.1 (0.6)10.3 (0.6)18.2 (0.9)58.6 (1.2)10.3 (0.8)12.9 (0.8)17.9 (0.7)54.1 (0.9)9.8 (0.5)18.2 (0.6)75.7
 1 to 218.3 (0.7)57.0 (0.9)10.7 (0.6)14.1 (0.6)14.0 (0.8)54.2 (1.2)12.3 (0.8)19.4 (0.9)13.1 (0.6)49.1 (0.8)13.7 (0.6)24.1 (0.7)71.3
 ≥313.8 (1.4)53.1 (2.2)12.9 (1.5)20.2 (1.9)14.6 (1.8)51.5 (2.8)13.9 (1.8)20.0 (2.1)9.4 (1.1)47.7 (1.9)14.0 (1.3)28.9 (1.7)43.0
Smoking during pregnancy             
 Yes24.8 (1.3)53.2 (1.5)10.2 (0.9)11.8 (1.0)20.6 (1.5)51.2 (2.0)10.5 (1.2)17.7 (1.5)20.0 (1.1)47.3 (1.4)10.9 (0.8)21.8 (1.1)84.6
 No18.9 (0.5)57.9 (0.7)10.2 (0.4)13.0 (0.5)14.8 (0.6)56.8 (0.9)11.9 (0.6)16.4 (0.6)13.8 (0.4)51.8 (0.6)12.3 (0.4)22.1 (0.5)69.2

Women with the highest prevalence of obesity in 2002 to 2003 were >20 years of age, were black, were parous, had a high school education, were enrolled in WIC, and were non-smokers (Table 3). These associations held in the adjusted analysis, with the exception of smoking, which was not associated with obesity (Table 4).

Table 4.  Adjusted relative risk* for pre-pregnancy overweight and obesity among women delivering live birth, PRAMS 2002–2003
CovariateOverweightObese
  • PRAMS, Pregnancy Risk Assessment Monitoring System; WIC, Women, Infants, and Children; ref, reference. Values are adjusted relative risk (95% confidence interval).

  • *

    Adjusted for all variables presented in the table.

  • Weight of pre-pregnancy overweight vs. lean/normal.

  • Weight of pre-pregnancy obese vs. lean/normal.

Age (yrs)  
 <20refref
 20 to 291.3 (1.0, 1.6)1.8 (1.5, 2.2)
 ≥301.4 (1.1, 1.7)1.9 (1.5, 2.3)
Race  
 Whiterefref
 Black1.4 (1.2, 1.6)1.5 (1.3, 1.6)
 Other0.8 (0.6, 1.0)0.7 (0.6, 0.9)
Education (yrs)  
 <120.9 (0.7, 1.1)0.9 (0.8, 1.1)
 121.1 (0.9, 1.2)1.1 (1.0, 1.3)
 ≥13refref
WIC enrollment  
 Yes1.2 (1.0, 1.4)1.4 (1.3, 1.6)
 Norefref
Parity  
 0refref
 1 to 21.4 (1.2, 1.6)1.3 (1.2, 1.4)
 ≥31.5 (1.2, 1.9)1.4 (1.2, 1.6)
Smoking during pregnancy  
 Yes0.9 (0.8, 1.1)0.9 (0.8, 1.1)
 Norefref

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

In this population-based assessment of obesity and pregnancy, we found that the prevalence of pre-pregnancy obesity increased substantially in all nine states. Increases in obesity were found in all subgroups of women, and the direct standardization results analysis indicated that this health issue is not caused by shifting population demographics. By 2002 to 2003, more than one in five women were obese at the beginning of pregnancy. Our study is the largest to date to examine trends in pre-pregnancy obesity in the United States; these nine states represent 18.5% of all live births in the United States (14).

The greatest increases in pre-pregnancy obesity were generally among women who had the lowest prevalence in 1993 to 1994. For example, women <20 years of age had the lowest percentage of obesity in 1993 to 1994 (7.2%) and one of the greatest increases in obesity by 2002 to 2003 (97.0%). This pattern suggests that all subgroups of women are experiencing increases in obesity and that those traditionally at lowest risk are catching up with those at highest risk.

Although our finding that pre-pregnancy obesity is increasing is consistent with previous studies (10, 11, 15, 16), more recent evaluations of obesity trends in non-pregnant women found no increase between 1999 and 2004 (17), and it is possible that obesity may be leveling off in pregnant women as well. The Institute of Medicine BMI categories are specific to pregnancy, but this classification includes more obese women than the widely used National Heart, Lung, and Blood Institute (NHLBI) categories. However, when we re-categorized our BMI data to conform to NHLBI guidelines, there was no difference in the trend between 1993 to 1994 and 2002 to 2003. Our finding that 22% of women were obese before pregnancy in 2002 to 2003 is slightly less than recent national estimates, in which obesity prevalence among non-pregnant women 20 to 39 years of age participating in National Health and Nutrition Education Survey was 28.9% in 2003 to 2004 (17). This difference could reflect regional variations in obesity and differences in the age distribution of women participating in PRAMS and those participating in the National Health and Nutrition Education Survey or in self-report vs. clinically measured BMI. In addition, National Health and Nutrition Education Survey uses an obesity cut-off of ≥30 kg/m2 based on the NHLBI BMI criteria. As expected, when we used the higher cut-off, the obesity prevalence in 2002 to 2003 was slightly lower (18.6%) than obesity prevalence based on Institute of Medicine criteria.

The growing burden of obesity among pregnant women will likely have substantial national health consequences. For example, pre-pregnancy obesity has been associated with an increased risk of gestational diabetes (GD) (3), and recent studies suggest that GD is rising in the United States (18, 19, 20). In a study of the Kaiser Permanente Medical Care Program in Northern California, the authors reported a 35% increase in GD between 1991 and 2000 among women 15 to 49 years of age (18). We were unable to evaluate the contribution of BMI to changes in the prevalence of GD in this study because of limited information about GD in this dataset. However, elevated BMI is strongly associated with GD and is likely contributing to the increasing incidence of GD reported in California and New York City (18, 21).

Cesarean delivery is another complication associated with obesity. Obese women have an ∼2-fold increased risk for cesarean section compared with normal-weight women (2). Between 1996 and 2004 in the United States, the overall rate of cesarean delivery increased 40%, from 20.7% to 29.1% of all births, and the primary cesarean rate increased 41%, from 14.6% to 20.6% (22). Although many factors contribute to changing cesarean rates (23, 24, 25, 26), increasing BMI or pre-pregnancy obesity may be playing a role.

Pre-pregnancy obesity also affects the health of infants born to obese mothers. Infants born to obese mothers have greater percentage body fat than infants of non-obese mothers, a marker for future risk of obesity and type 2 diabetes (27). In addition, children whose mothers were obese during the first trimester of pregnancy were 2.3 times more likely to be obese at 4 years of age (24.1%) than children whose mothers were not obese (9.0%), after adjusting for maternal demographic characteristics, infant birth weight, and smoking and weight gain during pregnancy (7). A longitudinal cohort study found that children exposed to maternal obesity were at a 2-fold increased risk of developing metabolic syndrome leading to type 2 diabetes (8). These studies suggest that the increase in maternal obesity is likely to lead to increases in childhood obesity and type 2 diabetes, potentially contributing to a recurring cycle of maternal obesity passed on to future generations.

A limitation of this study is that pre-pregnancy BMI was self-reported, and self-report has been shown to slightly underestimate BMI (9). Several studies in the past 10 years, including a nationally representative study, found that women tended to misrepresent their weight, with overweight women underestimating their weight and underweight women overestimating their weight (28, 29, 30). However, the magnitude of under-reporting for overweight women was <10 lbs, on average. Hence, a small percentage of obese women would be misclassified as overweight (28, 31). In addition, the trend in the increasing prevalence of obesity in our study may be underestimated. In a comparison of self-reported height and weight compared with measured height and weight using Behavioral Risk Factor Surveillance System and National Health and Nutrition Education Survey, underestimation of weight among American women actually increased slightly in the 1990s (31). Thus, the prevalence and the percentage increase in pre-pregnancy obesity may be greater than what was reported in this study.

Missing information about BMI is another limitation in that 9.4% of PRAMS participants did not provide their height and/or weight and, thus, were excluded from the analysis, potentially introducing bias into the study. However, the demographic characteristics of the women excluded for missing BMI did not change during the study period, suggesting minimal effects on trends findings. Last, we did not include Hispanic ethnicity in our paper because data on ethnicity were not available in our dataset for 1993 to 1994. Therefore, we were not able to examine ethnic-specific trends in pre-pregnancy obesity. In addition, we were not able to directly evaluate the potential contribution of growth of the Hispanic population in these nine states to pre-pregnancy obesity trends. However, using data from 2002 to 2003, in which Hispanic ethnicity was available, we found that Hispanics represented only 13% of the sample. Furthermore, the prevalence of obesity among Hispanic women (19%) was similar to that in non-Hispanic women (22%). Therefore, we conclude that including Hispanic ethnicity in the direct standardization analysis would not have influenced the results of our study.

In summary, pre-pregnancy obesity increased significantly over the last decade in all nine of the states studied, independently of demographic, obstetrical, and behavioral factors. Obesity is associated with increased risk of complications during pregnancy and at labor and delivery (1, 2, 3, 4, 5, 6). Therefore, the increasing prevalence of obesity poses unique challenges in the provision of prenatal care. Moreover, obesity is an important health concern across the lifespan for women. Although weight loss is not recommended during a woman's pregnancy, her consistent contact with health care providers during pregnancy and the puerperium provides an opportunity to promote appropriate physical activity and nutrition to mitigate the effects of obesity for future pregnancies and beyond.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Data from the Pregnancy Risk Assessment Monitoring System (PRAMS) included in this study are collected at the state level by the following state collaborators and their staff: Alabama—Louie Albert Woolbright; Alaska—Kathy Perham-Hester, MS, MPH; Florida—Helen Marshall; Maine—Kim Haggan; New York State—Anne Radigan—Garcia; Oklahoma—Dick Lorenz, MS; South Carolina— Sylvia Sievers; Washington—Linda Lohdefink; West Virginia—Melissa Baker, MA; CDC PRAMS Team, Applied Sciences Branch, Division of Reproductive Health. The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention. There was no funding/outside support for this study.

Footnotes
  • 1

    Nonstandard abbreviations: PRAMS, Pregnancy Risk Assessment Monitoring System; WIC, Women, Infants, and Children; NHLBI, National Heart, Lung, and Blood Institute; GD, gestational diabetes.

  • The costs of publication of this article were defrayed, in part, by the payment of page charges. This article must, therefore, be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
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