Effects of different data-editing methods on trends in race-specific preterm delivery rates, United States, 1990-2002

In recent years, national vital statistics data indicate that the US preterm delivery rate has decreased among African Americans and increased among whites. These trends in preterm delivery rates may have been affected, in part, by improvements in the accuracy of gestational age reporting on birth certificates. Several data-editing methods have been developed with the intention of reducing the percentage of records with misclassified gestational age. We explored whether three data-editing methods yielded different trends in preterm delivery for years 1990-2002 among US non-Hispanic white and non-Hispanic African American singleton livebirths. Using National Center for Health Statistics (NCHS) public-use data, we assessed two published methods for editing gestational age, one by Alexander et al. and the other by Zhang and Bowes (Zhang/Bowes). We also assessed a third method that substitutes the clinical estimate (CE) of gestational age when the NCHS last menstrual period (LMP)-based estimate differs from the CE by more than 2 weeks (the LMP/CE method). The percentage of records excluded and/or reclassified by each method was calculated for years 1990, 1996 and 2002. Gestational age-specific birthweight distributions were plotted by race for each method. Preterm delivery rates were calculated and compared by method of editing over time. The percentage of records excluded or reclassified declined from 1990 to 2002 regardless of the method applied. For infants at 28-33 weeks' gestation using the NCHS edited data, birthweight distributions were bimodal, with the second (right-sided) mode showing a mean birthweight consistent with that of term infants. The second mode was less pronounced using the Alexander et al. and the Zhang/Bowes methods, and was not present when the LMP/CE method was used. From 1990 to 2002, preterm delivery rates increased for non-Hispanic whites regardless of method (range 21.3-31.3%). Preterm delivery rates increased slightly for non-Hispanic African Americans with the LMP/CE method (1.8%), and decreased with the other methods (range 6.7-10.8%). Different approaches to editing gestational age from vital records can result in variation in preterm delivery rates and trends. Uncertainty persists around the true trends in preterm delivery, especially among African Americans. Additional research is needed to identify the approach that results in the most accurate classification of gestational age.