Stages of pregnancy 1 First trimester (week 1–week 12). 2 Second trimester (week 13–week 28). 3 Third trimester (week 29–week 40). 4 Your developing baby.
The end of the first trimester is at about week 12, at this point in your baby’s development: The nerves and muscles begin to work together. Your baby can make a fist. The external sex organs show if your baby is a boy or girl. Eyelids close to protect the developing eyes. They will not open again until week 28.
A typical pregnancy lasts 40 weeks from the first day of your last menstrual period (LMP) to the birth of the baby. It is divided into three stages, called trimesters: first trimester, second trimester, and third trimester.