Pregnancy Dating

Informs, shows its work. Naegele's rule: EDD = LMP + 280 days, assuming a certain LMP and a regular 28-day cycle with ovulation on day 14. Gestational age is dated from the LMP. This is a point estimate of a spread — most patients deliver across the 37–42 week term window, not on the date. First-trimester ultrasound (crown-rump length) is more accurate and supersedes LMP dating when the two disagree or the LMP is uncertain.