1 Week of Pregnancy

Baby's Growth and Development at Week One

It may seem strange, but your pregnancy journey begins before your baby even is conceived.

The first week of pregnancy actually begins with the start of your last menstrual period. Why? It's hard to pinpoint exactly when your egg becomes fertilized, but the date of your last cycle is a more accurate starting point. Your doctor will calculate your due date by counting 40 weeks from the start of your last menstrual period.

It's called the Gestational Age, and it's how most doctors measure pregnancies. Because ovulation and conception take place about two weeks after your period begins, your baby's Fetal Age (which begins when your egg is fertilized) will be two weeks less than his Gestational Age. So, when you're 8 weeks pregnant, your baby's fetal age is 6 weeks.