This document discusses how to determine a pregnant woman's expected date of delivery (EDD) and why accurate dating is important. It outlines four groups for determining EDD: 1) women with regular cycles based on last menstrual period, 2) women with irregular cycles based on ultrasound scans, 3) women conceiving through IVF based on embryo transfer date, and 4) women with multifetal pregnancies based on the larger fetus. The document emphasizes that the EDD determined early in pregnancy from last menstrual period or early ultrasound scans between 6-14 weeks is usually the most accurate. Subsequent scans may show different dates due to fetal growth variations, but the original EDD should not be changed. Accurate dating guides prenatal care