toggle mobile menu Menu
toggle search menu

Site Navigation

Supplemental

Menu

Embryo

When a fertilized egg has implanted in the uterus, the group of cells that will become a baby is called an embryo.

A developing, fertilized egg is known by several names within the first 2 weeks after conception, including zygote, morula (day 4), and blastocyst (day 5).

The embryonic period lasts until 8 weeks after conception (10 weeks from the last menstrual period). During this time, the embryo is forming major body structures, such as the head, spine, and internal organs. This is the time when most birth defects develop. After this point, the growing baby is called a fetus.

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. Healthwise is a URAC accredited health web site content provider. Privacy Policy. How this information was developed to help you make better health decisions.

© 1995- Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.