Pregnancy Due Date

Naegele's rule assumes a regular 28-day cycle and ovulation on day 14. Only about 5% of babies are born on their exact due date — most are born within 2 weeks either side. Ultrasound dating in the first trimester is more accurate and is used to confirm or adjust the due date.

The first trimester covers weeks 1–12, the second trimester covers weeks 13–26, and the third trimester covers weeks 27–40. Each trimester involves distinct developmental milestones and health considerations for both mother and baby.

Gestational age is measured from the LMP and is the standard used by healthcare providers. Fetal age (conceptional age) is measured from conception and is typically 2 weeks less than gestational age. When a doctor says you are 10 weeks pregnant, they mean 10 weeks gestational age.