Measuring Gestational Age in Vital Statistics Data: Transitioning to the Obstetric Estimate.

Beginning with the 2014 data year, the National Center for Health Statistics is transitioning to a new standard for estimating the gestational age of a newborn. The new measure, the obstetric estimate of gestation at delivery (OE), replaces the measure based on the date of the last normal menses (LMP). This transition is being made because of increasing evidence of the greater validity of the OE compared with the LMP-based measure. This report describes the relationship between the two measures. Agreement between the two measures is shown for 2013. Comparisons between the two measures for single gestational weeks and selected gestational age categories for 2013, and trends in the two measures for 2007-2013 by gestational category, focusing on preterm births, are shown for the United States and by race and Hispanic origin and state.