Abstract
Background. We studied the agreement between different measurements of gestational age, i.e. self-reported gestational age in the Danish National Birth Cohort Study, ultrasound-estimated gestational age from the medical records in one Danish county and gestational age from the Danish National Hospital Discharge Register. Methods. The ultrasound-estimated gestational length was based on the size of the biparietal diameter. The ultrasound-estimated gestational length was related to corrected and uncorrected last menstrual period estimates in the Danish National Cohort Study, and to the gestational length recorded in the Danish National Discharge Register. Non-parametric statistics were used in the analysis. Results. The gestational ages estimated by ultrasound were 2-3 days shorter than gestational ages estimated by the other methods. The gestational ages recorded by the Discharge Register and the gestational ages based on corrected last menstrual period did not differ significantly. Conclusion. The self-reported gestational age in The Danish National Birth Cohort is in good concordance both with data from the National Hospital Discharge Register and with ultrasound-estimated gestational age.