Chapter 53: Dating the Beginning of Pregnancy

This chapter describes how charting with the CREIGHTON MODEL FertilityCare System allows a pregnancy to be dated from the estimated time of conception (ETC), in contrast to gestational age measured from the first day of the last menstrual period. Hilgers explains how the ETC is taken as the midpoint between the earliest and last acts of intercourse during the time of fertility, with conventions for single acts of intercourse and even-numbered intervals, and gives a formula for the estimated time of arrival (ETA), or due date, from the ETC. In 173 consecutive pregnancies charted with the CrMS, the CrMS due date equaled the early ultrasound due date plus 1.97 days on average, and the two were within 10 days of each other in 100 percent of cases. The chapter argues that accurate dates reduce obstetrical interference and improve judgment in managing pregnancy, labor and delivery.