ABSTRACT
OBJECTIVE: The birth certificate variable obstetric estimate of gestational age (GA) has not been previously validated against GA based on estimated date of delivery from medical records. STUDY DESIGN: We estimated sensitivity, specificity, positive predictive value, negative predictive value and the corresponding 95% confidence intervals (CIs) for preterm delivery (<37 weeks' gestation) based on obstetric estimate using estimated date of delivery-based GA as the gold standard. Trained abstractors obtained the estimated date of delivery from the prenatal record (64.8% in New York City, and 94.6% in Vermont), or, when not available, from the hospital delivery record for 2 population-based samples: 586 live births delivered in New York City and 649 live births delivered in Vermont during 2009. Weights were applied to account for nonresponse and sampling design. RESULTS: In New York City, the preterm delivery rate based on estimated date of delivery was 9.7% (95% CI, 7.6-12.4) and 8.2% (95% CI, 6.3-10.6) based on obstetric estimate; in Vermont, it was 6.8% (95% CI, 5.4-8.4) based on estimated date of delivery and 6.3% (95% CI, 5.1-7.8) based on obstetric estimate. In New York City, sensitivity of obstetric estimate-based preterm delivery was 82.5% (95% CI, 69.4-90.8), specificity 98.1% (95% CI, 96.4-99.1), positive predictive value 98.0% (95% CI, 95.2-99.2), and negative predictive value 98.8% (95% CI, 99.6-99.9). In Vermont, sensitivity of obstetric estimate-based preterm delivery was 93.8% (95% CI, 81.8-98.1), specificity 99.6% (95% CI, 98.5-99.9), positive predictive value 100%, and negative predictive value 100%. CONCLUSION: Obstetric estimate-based preterm delivery had excellent specificity, positive predictive value and negative predictive value. Sensitivity was moderate in New York City and excellent in Vermont. These results suggest obstetric estimate-based preterm delivery from the birth certificate is useful for the surveillance of preterm delivery.
