Understanding Last Menstrual Period (LMP) and Pregnancy Dates

When a doctor asks for the first day of your last menstrual period (LMP), it is not because you have already conceived. The LMP is used to calculate your estimated due date (EDD) for pregnancy, which is typically around 40 weeks from the first day of your last period.

Ovulation, which is the process of releasing an egg from the ovary, usually occurs 14 days before the start of your next period. This means that if you have a 28-day cycle, you will typically ovulate on day 14. If you have sex on or around the day of ovulation, there is a chance that you could conceive.

If you do conceive, it will take the fertilized egg about 7 days to travel to the uterus and implant in the uterine lining. This process is called implantation. Once the embryo has implanted, it will begin to grow and develop.

The EDD is based on the assumption that ovulation occurs 14 days before the start of your next period and that implantation occurs 7 days after ovulation. However, these are just averages and there can be some variation from woman to woman. This is why the EDD is an estimate and not an exact date.