Your Baby is the Size of a -------

How big is my baby at 3 weeks?

You ovulated this week, and the moment you’ve been waiting for has finally arrived: You’ve conceived! Meaning your soon-to-be-fetus has started on its miraculous transformation from solitary cell to bouncing baby boy or girl.

Once the winning sperm makes its way through the egg's outer layer, the single-cell fertilized egg — or zygote — immediately forms a barrier to keep other sperm out.

But your zygote doesn't stay single for long. Within hours, it divides into two cells, then four, and so on, until the growing cluster comprises around 100 cells just a few days after that crucial first meeting between sperm and egg. Some will form the embryo, others the placenta, but for now, it’s still just one microscopic ball of cells that’s one-fifth of the size of the period at the end of this sentence. 

Implantation

Tiny? Yes. But don't underestimate its potential. As it divides, the blastocyst, as it's now called (don't worry, you'll come up with a cuter name soon), travels this week from your fallopian tube to your uterus — a trip that takes about five or six days.

Spoiler alert: Once it arrives during week 4, it will implant itself in the uterine wall and grow for the next nine months. In other words, congratulations! You've got yourself a baby-in-the-making, ready to begin the incredible journey that will end in your arms.

Boy or girl?

So will your lone little cell miraculously become a girl or a boy? Though it will be months before you can find out for sure (if you decide to find out before delivery day), that remarkable determination has already been made, believe it or not.

Ready for a crash course in biology? The fertilized egg contains 46 chromosomes — 23 from each biological parent. The mother always provides an X chromosome, but the father can provide either an X or a Y. If the sperm that fertilizes your egg carries an X, the XX zygote will be a girl. If the sperm is Y-bearing, your XY zygote will be a boy.

The Mutlu Anne app is with you every step of the way on your pregnancy journey.

Thanks for reading.