Validity of Birth Certificate‐Derived Maternal Weight Data

Abstract

Background Studies using vital records-based maternal weight data have become more common, but the validity of these data is uncertain. Methods We evaluated the accuracy of prepregnancy body mass index (BMI) and gestational weight gain (GWG) reported on birth certificates using medical record data in 1204 births at a teaching hospital in Pennsylvania from 2003 to 2010. Deliveries at this hospital were representative of births statewide with respect to BMI, GWG, race/ethnicity, and preterm birth. Forty-eight strata were created by simultaneous stratification on prepregnancy BMI (underweight, normal weight/overweight, obese class 1, obese classes 2 and 3), GWG (<20th, 20–80th, >80th percentile), race/ethnicity (non-Hispanic white, non-Hispanic black), and gestational age (term, preterm). Results The agreement of birth certificate-derived prepregnancy BMI category with medical record BMI category was highest in the normal weight/overweight and obese class 2 and 3 groups. Agreement varied from 52% to 100% across racial/ethnic and gestational age strata. GWG category from the birth registry agreed with medical records for 41% to 83% of deliveries and agreement tended to be the poorest for very low and very high GWG. The misclassification of GWG was driven by errors in reported prepregnancy weight rather than maternal weight at delivery, and its magnitude depended on prepregnancy BMI category and gestational age at delivery. Conclusions Maternal weight data, particularly at the extremes, are poorly reported on birth certificates. Investigators should devote resources to well-designed validation studies, the results of which can be used to adjust for measurement errors by bias analysis.

Validity of birth certificate‐derived maternal weight data in twin pregnancies

“…These factors could lead to important differences in the accuracy of maternal weight data on birth certificates. Nevertheless, our study suggests that the degree of error is similar to what we and others previously observed among singletons (Bodnar et al 2014) (Vinikoor et al 2010; Park et al 2011; Wright et al 2012). …”

“…This method is unlikely to lead to significant bias in our validation results because there is a strong correlation between measured prepregnancy weight and prepregnancy weight recalled at the first visit (Lederman & Paxton 1998; Phelan et al 2011; Mandujano et al 2012). Furthermore, we previously demonstrated in singletons that the agreement proportions for birth certificate-derived BMI and GWG categories with medical-record categories were similar when we used measured weight at ≤8 weeks or prepregnancy weight recalled at the first visit (Bodnar et al 2014). …”

“…The study design, setting, and methods of data collection were the same for the twin validation as for the singleton validation, and have been presented in detail previously (Bodnar et al 2014). The U.S. birth certificate collects self-reported prepregnancy height and weight via interview before discharge (CDC National Center for Health Statistics 2003), which we validated against self-reported prepregnancy weight and height at first prenatal visit [median 9 (interquartile range 7–11) weeks gestation].…”

“…We calculated exact binomial 95% confidence intervals for the agreement proportions. To determine whether the agreement proportions for birth certificate-derived BMI and GWG categories among twins were similar to singletons, we compared results from the singleton validation sample (Bodnar et al 2014) after weighting them to reflect the race-ethnicity and preterm birth distribution of the twins validation sample. A Fisher’s exact test was used to compare proportions.…”

“…Nevertheless, there is concern that information on maternal height, prepregnancy weight, and weight at delivery from vital records is inaccurate because it is based on self-report (Institute of Medicine 2009), and that this misclassification may lead to biased associations with adverse perinatal outcomes (Bodnar et al 2010). We recently undertook a large validation study of birth certificate-derived data on prepregnancy BMI and GWG compared with medical record information among singleton births in a Pennsylvania hospital and found poor agreement, particularly for extremes of maternal weight (Bodnar et al 2014). In this paper, we expand this analysis to determine whether vital records BMI and GWG data among twin pregnancies are accurate enough to be used without major concern about misclassification bias, or whether measurement error requires that conventional associations between maternal weight and adverse outcomes be adjusted for the bias (Fox et al 2005; Lash et al 2009; MacLehose & Gustafson 2012; Lash et al 2014).…”