New Recommendations for Estimating Due Dates

By Kelly Young

Edited by David G. Fairchild, MD, MPH, and Jaye Elizabeth Hefner, MD

The American College of Obstetricians and Gynecologists, along with the American Institute of Ultrasound in Medicine and the Society for Maternal-Fetal Medicine, have published standardized recommendations on how to best estimate a due date for a pregnant woman. The guidance appears in Obstetrics & Gynecology.

The groups note that, traditionally, the first step in estimating a due date is adding 280 days to the woman's last menstrual period. Beyond that, they make the following recommendations:

• The most accurate method of establishing or confirming gestational age is measuring the fetus' crown-rump length via high-quality ultrasound in the first trimester (accuracy of +/- 5-7 days).

• If assisted reproductive technology (ART) was used, the due date should be estimated by the ART-derived gestational age (e.g., age of embryo and date of transfer).

• Changes to the estimated due date should be done only in rare instances, discussed with the patient, and documented in the medical record.