Predicting date of birth and examining the best time to date a pregnancy

To compare the estimated date of birth (eDOB) from the last menstrual period (LMP) and ultrasound scans at varying gestations (<7(0), 7(0)-10(6), 11(0)-14(0), 14(1)-19(6), and 20(0)-27(6)weeks) with the actual date of birth (aDOB).

In a retrospective study, data were analyzed from 18 708 women with spontaneous labor who delivered a single neonate without major anomalies in a local health district in Australia between 2007 and 2011. Data were sourced from a computerized population birth database. The study outcomes were duration of pregnancy expressed as total days, and the difference between aDOB and eDOB by dating method.

Only 5% of births occurred on the eDOB, regardless of the dating method or timing of the dating. Approximately 66% of births occurred within 7days of the eDOB, and there was little difference among the ultrasound examinations performed at varying gestational weeks. The ultrasound scans at 11(0)-14(0)weeks of gestation performed as well as ultrasound scans conducted at other gestational ages.

On a population basis, there were no meaningful differences in the prediction of date of birth by ultrasound scan date. An early dating scan (≤10weeks) is unnecessary if LMP is reliable.