Fetal development


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

Alternative Names

Zygote; Blastocyst; Embryo; Fetus



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 your 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


Feigelman S, Finkelstein LH. Assessment of fetal growth and development. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 20.

Ross MG, Desai M, Ervin MG. Fetal development, physiology, and effects on long-term health. In: Landon MB, Galan HL, Jauniaux ERM, et al, eds. Gabbe's Obstetrics: Normal and Problem Pregnancies. 8th ed. Philadelphia, PA: Elsevier; 2021:chap 2.

Review Date: 8/23/2023
Reviewed By: LaQuita Martinez, MD, Department of Obstetrics and Gynecology, Emory Johns Creek Hospital, Alpharetta, GA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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