Week 4 · First trimester
Week 4, gently.
Your baby is the size of
a poppy seed
- 0.2 cm long
Your baby has only three layers of cells this week — those three will become every part of a whole person.
“Three soft layers, already arranging themselves into everything.”
What’s happening inside
The embryo has three layers: the ectoderm (future brain and skin), the mesoderm (heart, bones, muscles), and the endoderm (lungs, digestive system). The placenta is beginning to form.
How you might feel
Your period is now officially late. A home pregnancy test is likely reliable around now. You may feel tender, tired, a little queasy, or nothing at all — all of it is normal.
