Validation of obstetric estimate of gestational age on US birth certificates

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.

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.

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%.

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.