Fetal development: Your baby’s growth in the womb

So much is going on inside your body and mind to prepare for your baby! Here are some details to help you understand this fascinating time in your pregnancy through each stage of fetal development.

The beginning of fetal development

Three days after fertilization the cluster of now several dozen cells begins moving down your fallopian tube to your uterus, an “embryo” from the day when you would have expected to have your next period until the end of the second month (an arbitrary time selection), when it’s called a “fetus.”

To estimate your due date, add seven days to the first day of your last menstrual period and subtract three months. You can also try this due date calculator from the American Pregnancy Association: Pregnancy Calculator.

Month 1

At the beginning of this month, the fertilized egg is a fluid-filled cluster of rapidly multiplying cells. The egg tunnels into the uterus, where it promptly divides into two parts. Half the egg attaches to the uterine wall and develops into the placenta, which will transport oxygen and nutrients to Baby and waste products away from your baby during the next nine months. The other half will develop into the embryo, which will later become the fetus.

During this month the following occurs:

• Spinal cord development. A sheet of cells on the back of the embryo folds in the middle to form a tube, which will become the baby’s spinal cord.
• Brain section development. At the other end the tube enlarges to form the brain's major sections.

Learn more about the first month of pregnancy:
Week 1
Weeks 2 to 3
Week 4

Month 2

Although the embryo measures less than ¼ inch at the beginning of this month, by the end of the month it’s longer and curled into the fetal position. Because it’s difficult to measure the full length with the legs drawn up, measurements are more commonly made from the top of the head to the buttocks.

• Organ formation. By this stage of fetal development, all of your baby’s main organs have started to form.
• Body parts formation. The baby has fingers, toes, and bumps on either side of his head that are early ears.

Learn more about the second month of pregnancy:
Week 5
Week 6
Week 7
Week 8

Month 3

Your baby is now technically called a fetus and about the size of a grape.

• Organ systems. Your baby has all of the organ systems in place.
• Movement. With stimulation your baby may squint, open her mouth, and flex fingers and toes. Because the fetus is still relatively small, you won’t feel this movement.
• Brain function. Your baby’s head is becoming more rounded, and her brain, nerves, and muscles begin to function.

Learn more about the third month of pregnancy:
Week 9
Week 10
Week 11
Week 12