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 about 8 weeks after conception (about 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.
| Author | Jeannette Curtis |
| Author | Caroline Rea, RN, BS, MS |
| Editor | Kathleen M. Ariss, MS |
| Editor | Susan Van Houten, RN, BSN, MBA |
| Associate Editor | Tracy Landauer |
| Associate Editor | Pat Truman |
| Primary Medical Reviewer | Patrice Burgess, MD - Family Medicine |
| Primary Medical Reviewer | Adam Husney, MD - Family Medicine |
| Primary Medical Reviewer | Kathleen Romito, MD - Family Medicine |
| Last Updated | May 25, 2007 |
WebMD Medical Reference from Healthwise
Last Updated:
May 25, 2007
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