1st trimester · Week 3
3 weeks pregnant
Fertilization and a traveling cluster of cells
If fertilization occurred, a zygote becomes a morula and then a blastocyst while moving toward the uterus. Implantation may start at the end of this week or early next week. A home test is often still negative.
How is your baby developing at 3 weeks?
The cluster of cells is microscopic — closer to a grain of rice only as a loose comparison. Inner cells will later form the embryo; outer cells help make placenta and membranes. Many fertilized eggs do not implant; that can be a normal biological outcome.
What changes in your body at 3 weeks?
You will usually feel like your usual premenstrual self. Some people have no symptoms. Light spotting can occur later with implantation, but spotting has many causes and is not a test of pregnancy.
Tips for this week
Keep taking folic acid. Avoid alcohol if there is any chance you conceived. A home pregnancy test is more reliable after a missed period. If you have severe one-sided pain or heavy bleeding, seek care — those symptoms need a clinician, not an app.
