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4 weeks

What Is The Difference Between An Embryo And A Fetus?

Baby was an embryo and is now a fetus. What does that mean?

It’s a different phase of baby’s development. “The embryo is defined as the developing pregnancy from the time of fertilization until the end of the eighth week of gestation, when it becomes known as a fetus,” says James A. O’Brien, MD, ob-gyn, medical director of inpatient obstetrics at Women & Infants Hospital of Rhode Island.

 During the embryonic period, cells begin to take on different functions. The brain, heart, lungs, internal organs, and arms and legs begin to form. Once baby is a fetus, it’s more about growth and development to prep for life on the outside.

Plus, more from The Bump:

What Is Implantation Bleeding?

Most Common Symptoms of Pregnancy

First Trimester To-Dos

By James A. O'Brien, MD