Issues in Pregnancy Dating: Revisiting the Evidence


  • Linda A. Hunter CNM, EdD

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    • Linda A. Hunter, CNM, EdD, is a Clinical Assistant Professor in Obstetrics and Gynecology at the Warren Alpert Medical School of Brown University. She is also in clinical practice on the nurse-midwifery faculty in the Department of Obstetrics and Gynecology at Women & Infants Hospital in Providence, RI.

Nurse-Midwifery Division, Women & Infants Hospital, 101 Dudley St., Providence, RI 02905. E-mail:


As the end point date in pregnancy, the estimated date of delivery provides guidance for the timing of specific prenatal tests, gauges fetal growth, and informs critical decision making for specific obstetric complications. It is prudent to use the most evidenced-based methods available to accurately determine gestational age. This article explores the accuracy of both menstrual and ultrasound dating techniques and discusses some of the issues and limitations for each method. In addition, a simple formula called the rule of eights can be used to determine a final estimated date of delivery when a discrepancy between menstrual and ultrasound dating occurs.