As recommended by other investigators, this study examined the accuracy of prepregnancy BMI (height and prepregnancy weight) and GWG records using South Carolina birth certificate data compared to EMR abstracted data, which is the gold standard [5, 6, 7]. The study used data from a subsample of pregnant women who participated in the CenteringPregnancy group-based prenatal care program from 2015 to 2019 in three out of five obstetric sites in the Midlands of South Carolina. Women participating in the program and those receiving standard prenatal care were sufficiently similar regarding their characteristics, and the results from one source applied to the other. Overall, birth certificate mean estimates for height (r = 0.94), prepregnancy weight (r = 0.93), prepregnancy BMI (r = 0.92), and delivery weight (r = 0.96) largely correlated with the EMR data. Total weight gain was also correlated (r = 0.60) but not as strongly as the other variables. The mean differences in the variables between both data sources were quite small. A considerable number of women had height and weight at delivery values on birth certificates that were within a good reporting range of the EMR. Underreporting was common for prepregnancy weight, prepregnancy BMI and total weight gain. Prepregnancy body mass index (BMI) categories (underweight, normal weight, overweight, obese) for birth certificates agreed with those of EMRs, although birth certificates classified slightly fewer women as having normal weight and slightly more as being overweight compared to EMR abstracted data. For BMI categories, the BC data were both reasonably precise and accurate (PPV range between 69% and 89%) and somewhat all-inclusive (sensitivity range between 67% and 88%).
Prepregnancy weight values that were underreported were most likely to have contributed to the misclassification of prepregnancy BMI categories. This variable can be improved upon by measuring the weight at the first prenatal visit or just prior to conception for quality assurance and avoiding the use of self-reported figures. Additionally, birth certificate gestational weight gain categories (inadequate, adequate, excessive) were similar to those in the EMR data, although birth certificates classified slightly more women as having inadequate weight gain, i.e., below the IOM recommendation, and slightly fewer women as having excess weight gain in comparison to medical records. Regarding GWG categories, birth certificate data are reasonably accurate (PPV between 64% and 84%) and moderately inclusive (sensitivity ranges between 71% and 76%). As mentioned before, improvement in prepregnancy weight documentation can improve data on prepregnancy BMI categories, therefore enhancing GWG measurements and its categorization and avoiding misclassification. Our findings show that birth certificate data can provide reasonable estimates of these variables, at least in South Carolina.
Previous studies suggested the need for the validation of the quality of these variables (prepregnancy BMI and GWG and their categories) in birth certificate data because of mixed results or findings from prior studies on group-based prenatal care programs, with some showing a positive association, some showing a negative association and some showing no significant difference [19]. The findings from these studies (summarized in Appendices 2 and 3) are contrary or inconsistent with our results with respect to BMI and GWG categories, although the mean estimates of related variables were close to that of the gold standard. For example, Park’s study in Florida in 2005 investigated the reliability and validity of height, weight and prepregnancy BMI records in the Women, Infants and Children (WIC) Nutrition Program dataset compared to birth certificates (gold standard) and found that WIC data minimally overestimated the prevalence of underweight and normal weight and slightly underestimated the prevalence of overweight and obesity according to BMI. The study did not evaluate GWG. [10] The difference in findings was also noted in Bodnar’s study in Pennsylvania in 2014 and the Deputy study in New York and Vermont in 2018, which compared prepregnancy BMI and GWG data from birth certificates and PRAMS with data from EMRs (gold standard). Some of the variables were slightly overestimated or underestimated compared to the gold standard (EMRs). The reasons for the variation in results may be because the studies were carried out in different states with different populations of women and also because some studies used different gold standards, such as birth certificates. South Carolina data add to current knowledge, as the state has a population that may differ from other states in which similar work was done. It is important that researchers continue to monitor the accuracy of data for these variables on birth certificates. Researchers should continue to put effort into screening or evaluating the quality of maternal prepregnancy BMI and GWG categories in birth certificate data in different settings, as high-quality data give accurate, consistent, and reliable results in quantitative research that can better inform decision-making for health services policies. Overall, the South Carolina birth certificate form still provides a reasonable estimate of the prevalence of these variables for research purposes, for example, in examining the effect or impact of different prenatal care programs.
The strength of this validation study is that it validated the use of South Carolina birth certificate data for studies of prenatal care programs. We recognized the various limitations of our study. In addition to being limited to a single state, our study population was largely reflective of the experience of African American women who are between the ages of 20 and 29 years with at least a high school diploma, so future studies should consider a different age group in the same or different populations and different settings. Additionally, the sample size is another limitation, so we recommend that future studies expand on this limitation. Nevertheless, the results from our validation study show that in South Carolina, birth certificate estimates for height, prepregnancy BMI (and categories), prepregnancy weight, delivery weight and gestational weight gain categories were similar to those of electronic medical records; thus, the South Carolina birth certificate database is a valid database that can provide reasonable estimates for these variables for public health practice, future research purposes and particularly for the state’s evaluation of the CenteringPregnancy program.