These are the stages of a child's growth during the first trimester, starting at Week 3:
- Week 3 - Your baby is a microscopic cluster of cells. This is the stage during which the sperm and egg unite to form a zygote, or a tiny one-celled structure. As the zygote moves, the cells divide very quickly and form a blastocyst, or cluster of hundreds of cells.
- Week 4 - The embryo is only about 1/2 to 1 mm long! It already has two layers—the epiblast and the hypoblast—that will eventually develop into organs.
- Week 5 - The embryo already has three layers: the ectoderm, mesoderm, and ectoderm. It’s only about 1 to 3 mm long!
- Week 6 - Your baby's heart is beating and its facial features are forming. Your baby is about a quarter inch long.
- Week 7 - Your baby's facial features are becoming more defined, and little paddle-like hands are developing. Your baby is about a half an inch long, or the size of a blueberry.
- Week 8 - Your baby is starting to move! (You can’t really feel it yet, though.) Your baby is a little over half an inch long, or the size of a lima bean.
- Week 9 - Your baby has developed many of its physical characteristics and looks like a human. Your baby is around an inch long, which is the size of an olive or grape.
- Week 10 - Your baby is officially considered a fetus. It's a little over an inch long.
- Week 11 - Your baby is about one and one-half to two inches long, or about the size of a fig. Your baby's head makes up half of its entire length.
- Week 12 - Your baby is around three inches long, or about the size of a large lime. Even though length is still the best way to determine the size, your baby weighs almost an ounce this week!
