How Is Pregnancy Week Calculated?
Pregnancy weeks are counted from the first day of your last menstrual period (LMP). While actual conception typically occurs about 2 weeks after LMP, medical practice counts from LMP as the standard starting point. A full-term pregnancy spans 40 weeks (280 days), divided into three trimesters.
The first trimester (weeks 1–12) is when major organs form — a critical period for the developing embryo. The second trimester (weeks 13–27) brings rapid fetal growth and the appearance of movement. The third trimester (weeks 28–40+) involves final fetal development and birth preparation. The due date is estimated by adding 280 days to LMP (Naegele's rule).
Frequently Asked Questions
Using Naegele's rule: LMP + 280 days (40 weeks). Actual delivery typically occurs within 2 weeks before or after this date.
Pregnancy is divided into three trimesters: 1st (weeks 1-12), 2nd (weeks 13-27), and 3rd (weeks 28-40+), each with distinct developmental milestones.
Morning sickness typically begins around weeks 4–8 and usually improves by the end of the first trimester. Severity varies significantly between individuals.