Naegele Rule Edd

The estimated due date (EDD) is not a promise that birth will occur on one particular day. It is the reference point used to express gestational age and schedule care. Screening windows, anatomy assessment, fetal growth interpretation, viability discussions, preterm-birth management, and induction decisions all depend on the pregnancy being dated as accurately as possible. Gestational age is conventionally counted from the first day of the last menstrual period (LMP), not from fertilization. Because ovulation and fertilization usually occur about 2 weeks after the LMP, gestational age is approximately 2 weeks greater than embryonic or conceptual age. A pregnancy described as 10 weeks' gestation therefore usually represents about 8 weeks since conception. The EDD should be established early, discussed with the pregnant person, and recorded clearly. Once a reliable date has been selected, repeatedly changing it creates confusion and can shift time-sensitive care into the wrong gestational window.