If your period is regular and lasts 28 days, and if ovulation generally happens on day 14 of your cycle, then conception probably took place about two weeks after the LMP. For gestational age counting, these two weeks are added to a pregnancy as a simpler method than trying to track from ovulation or fertilization.

Do they always add 2 weeks to pregnancy?

To clarify, the gestational period of 40 weeks actually starts with the first day of your last period, which adds two weeks of time to the gestational period when your baby didnt even exist yet…

Can ultrasound be wrong about how many weeks pregnant?

Evidence suggests that ultrasounds more accurately predict your due date than using your last menstrual period—but only in the first trimester and early second trimester (until roughly 20 weeks). 3 Early ultrasound due dates have a margin of error of roughly 1.2 weeks.

When do I start to feel pregnant?

Early Pregnancy Symptoms It can occur from one to four weeks after the first day of your last period. Sometimes women feel cramping around the time of implantation (when the fertilized egg attaches to the uterus lining), which happens ten to fourteen days after conception.