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

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- It's implantation time!

Now, no bigger than a poppy seed, but a whole lot sweeter,

the ball of cells that will become your baby

has completed its week-long 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 stared 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 baby's vital organs are firmly in place.

(bright upbeat music)