Fetal development


Learn how your baby is conceived and how your baby develops inside the mother's womb.



Gestation is the period of time between conception and birth when a baby grows and develops inside the mother's womb. Because it's impossible to know exactly when conception occurs, gestational age is measured from the first day of the mother's last menstrual cycle to the current date. It is measured in weeks.

This means that during weeks 1 and 2 of pregnancy, a woman is not yet pregnant. This is when her body is preparing for a baby. A normal gestation lasts anywhere from 37 to 42 weeks.

Week 1 to 2

Week 3

Week 4

Week 5

Weeks 6 to 7

Week 8

Week 9

Week 10

Weeks 11 to 14

Weeks 15 to 18

Weeks 19 to 21

Week 22

Weeks 23 to 25

Week 26

Weeks 27 to 30

Weeks 31 to 34

Weeks 35 to 37

Week 38 to 40

Review Date: 6/30/2019
Reviewed By: John D. Jacobson, MD, Professor of Obstetrics and Gynecology, Loma Linda University School of Medicine, Loma Linda Center for Fertility, Loma Linda, CA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

This information should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. © 1997- 2007 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.