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Health & Pregnancy

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Your Pregnancy Week by Week: Weeks 1-4

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Week 3

Baby: Congratulations! If your egg and your partner's sperm have joined successfully, your embryo is really there, although it's very small -- about the size of the head of a pin. It doesn't look like a fetus or baby; it's just a group of about 100 cells multiplying and growing rapidly. The outer layer of cells will become the placenta, and the inner layer will become the embryo.

Mom-to-be: You won't notice any changes in your body at this point. Remember, you haven't even missed your period yet.

Tip for the Week: Can't wait to find out? Take a home pregnancy test. They're about as reliable as a urine test or blood test done in the doctor's office -- and you get results immediately. To ensure accuracy, read the directions carefully and make sure all the supplies you use are clean.

Week 4

Baby: Now that your egg is fertilized, it burrows into the lining of your uterus. This is called implantation.

Mom-to-be: You're probably expecting your period this week, and if it doesn't occur, it might be one of the first signs that you're pregnant. You may also notice light spotting as the embryo implants itself in your uterus. You might not feel any different yet, but the amniotic cavity, which will be filled with fluid, and the placenta, which will bring oxygen and nutrients to nourish your baby, are forming in your uterus.

Tip for the Week: Try to eat healthfully, which means choosing a variety of foods from recommended food groups and drinking at least six to eight 8-ounce glasses of water a day. But you don't really need to "eat for two"; you only need an extra 300 calories per day while you're pregnant. And don't worry if your food intake drops in the beginning because of morning sickness. If you've been eating right already, your baby will get what it needs.

What's Happening Inside You?

end of first month

The fertilized egg grows, and a water-tight sac forms around it, gradually filling with fluid. This is called the amniotic sac, and it helps cushion the growing embryo.

The placenta also develops. It is a round, flat organ that transfers nutrients from you to the baby and transfers baby’s wastes.

A primitive face takes form with large dark circles for eyes. The mouth, lower jaw, and throat are developing. Blood cells are taking shape, and circulation will begin.

By the end of the first month, your baby is about 1/4 inch long --smaller than a grain of rice.

WebMD Medical Reference

Reviewed by Kecia Gaither, MD, MPH on September 20, 2014
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