How long is term pregnancy?

When is baby coming? Traditionally obs consider a due date to be 40 weeks after the last normal menstrual period (lmp) and a term pregnancy to be 38 to 42 weeks. However, conception occurs approximately two weeks after the lmp. Also many people stick to talking about nine months being the length of pregnancy. Confused? You are not alone. Med students often scratch their heads. Ask your OB at each visit how many weeks.