What is gestational age?

Gestational age is the age of an unborn baby, or fetus. It is measured in weeks and days and is based on the date of your last menstrual period. Your healthcare provider will talk about your pregnancy in terms of weeks, not months. There are three stages of each pregnancy, called trimesters. The first trimester is from the 1st week through the 13th week. The second trimester is from the 14th through the 27th week, and the third trimester is from the 28th week to delivery.