The study population consisted of 522,315 infants born to maternal residents of five central counties of metropolitan Atlanta during the period 1995–2005. The final sample included 2,273 infants with anencephaly, spina bifida, cleft lip with or without cleft palate, clubfoot, Down syndrome, or rectal atresia or stenosis identified by MACDP or reported on a birth certificate. Of those, 2,251 infants met the MACDP case definition for at least one of the selected birth defects, and 550 infants had at least one of the selected birth defects noted on their birth certificate. A total of 86 infants had more than one of the selected defects reported; seven were noted in both sources, 74 were reported in MACDP only, and four were reported on birth certificates only. Approximately 23% of the selected birth defects ascertained by MACDP also were reported on birth certificates (). The sensitivity of birth certificates varied according to type of defect and ranged from 7% for rectal atresia or stenosis to 69% for anencephaly. The combined PPV was 96%, and was >90% for all defects except clubfoot (87%).
Sensitivity and PPV for birth certificate diagnoses for selected birth defects identifiable at birth, 1995–2005
The sensitivity of birth certificates for the combined group of defects differed significantly by maternal race/ethnicity and education, gestational age, and hospital size (i.e., mean annual number of births) (). These variables also were significantly associated with a lower probability of a true birth defect diagnosis on birth certificates in the adjusted models. For example, compared with non-Hispanic white mothers, infants born to mothers of non-Hispanic black and other non-Hispanic races/ethnicities were less likely to have a birth defect diagnosis correctly reported on a birth certificate. A maternal education of less than high school and preterm birth also were associated with decreased sensitivity. Finally, the odds of the accurate reporting of a birth defect diagnosis on birth certificates decreased with increasing hospital size. Overall, hospital-specific sensitivity varied and ranged from 0% to 100% (data not shown). Among the largest hospitals (>2,500 mean annual births) the sensitivity ranged from 1% to 58%.
Sensitivity and AOR estimates for associations among maternal, infant, and hospital characteristics and having a true birth defect diagnosis on birth certificates for selected birth defects identifiable at birth, Atlanta, 1995–2005
Overall, non-Hispanic black race/ethnicity and delivery in a large hospital were negatively associated with a report of cleft lip with or without cleft palate, clubfoot, and Down syndrome (). Specifically, among infants with cleft lip with or without cleft palate ascertained by MACDP, non-Hispanic black race/ethnicity, maternal education of less than high school, and delivery in a hospital with ≥1,000 mean births per year were associated with reduced sensitivity of birth certificates. Non-Hispanic black race/ethnicity, maternal age of younger than 35 years, maternal education of less than high school, preterm delivery, and large hospital size also were negatively associated with accurate reporting of a clubfoot diagnosis on birth certificates. For Down syndrome, low sensitivity was associated with non-Hispanic black and other non-Hispanic race/ethnicity, nulliparity, and delivery in a hospital with >2,500 mean annual births.
Defect-specific AORs for the association between selected maternal, infant, and hospital characteristics and having a true birth defect diagnosis on birth certificates, Atlanta, 1995–2005
The depicts trends in the overall and race/ethnicity-specific prevalences of the combined group of birth defects identifiable at birth, calculated using cases identified via MACDP and cases identified using birth certificates. Overall, the MACDP and birth certificate prevalence estimates were stable over time; however, there was a fourfold difference in the estimates, with the MACDP estimates ranging from 43.2 per 10,000 births in 1995 to 43.3 per 10,000 births in 2005, compared with 10.4 per 10,000 births and 11.6 per 10,000 births, respectively, for birth certificate data. The variations in the prevalence estimates varied by race/ethnicity. For example, the MACDP estimates for infants born to non-Hispanic black and Hispanic mothers were about five times higher than the birth certificate estimates for mothers of the same race/ethnicity. In comparison, there was generally a threefold difference noted in the prevalence estimates for non-Hispanic white people.
Three-year simple moving mean of prevalence of selected birth defects identifiable at birth by race/ethnicity for birth certificate and MACDP data, Atlanta, 1995–2005