4 Weeks Pregnant – What to Expect Your 4th Week of Pregnancy

by Claire October 15, 2015, 4:04 am 1.9k Views 48 Comments

It’s implantation time! Now no bigger than a poppy seed, though a whole lot sweeter, the ball of cells that will become your baby has completed its weeklong voyage down your fallopian tube and has claimed its berth in your uterus by tunneling into the sticky uterine lining. Nestled in your uterine home, this miniature miracle has established the cozy connection that will bind the two of you for the next eight plus months and forever after.

But that’s just the beginning of the action this week. In the works is the amniotic sac that your baby will call home sweet home. And at last! The sign you’ve been waiting for. Your little embryo starts to produce HCG, the just-for-pregnancy hormone that’ll turn your pregnancy pee test positively positive. You are officially expecting!

Though your embryo is only a tiny dot, it has already started to differentiate into three layers, each with its own job assignment. The inner layer, called the endoderm, will become the digestive system, the liver, pancreas, bladder, and thyroid gland.

The middle layer, the mesoderm, will grow into the heart, bones, kidneys, muscles, and blood vessels. The outer layer, called the ectoderm, will develop into the brain, nervous system, skin, hair, and eyes. It’s hard to believe, but by the end of your fourth week of pregnancy, all the building blocks for your baby’s vital organs are firmly in place.

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Written by Claire

Claire is our Community Manager here at New Moms Forum. A mom of two (almost grown-up babies), Claire has been building and operating community-based websites for almost 20 years. In her downtime, Claire enjoys spending time with her family and drinking copious amounts of red wine!