The fertilized egg is now a zygote. Which I originally thought was the creature Gandalf fought in the Lord of the Rings, but that was a Balrog. My bad.

It travels down the fallopian tube for a few days and divides to form a ball of wee cells that are even smaller than the period at the end of this sentence.

The zygote continues to divide, creating an inner group of cells with an outer shell (I like to envision an M&M but I doubt that’s the case) becoming a blastocyst. The blastocyst implants itself on your uterine wall around day six.

3 Weeks Pregnant Cheat Sheet:

  • Sperm and egg have met and created a zygote in one of your fallopian tubes
  • The zygote starts dividing to form a cluster of cells (a morula ) while traveling down the fallopian tube toward the uterus.
  • You have around 259 days before you give birth.
First trimester pregnancy timeline showing fetal development from month 1 to 3, with a marker on week 3.

Amy Morrison is the founder of Pregnant Chicken, a no-BS pregnancy and parenting site she started in 2010 after getting fed up with patronizing baby advice. A former ad agency creative director and mom of two boys, she's been serving up honest, funny guidance to parents-to-be ever since.

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