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My Baby - Week by Week Pregnancy

Week 4 - Implantation

Your baby is entering the embryonic period, during which the brain, spinal cord, heart and other organs will form.

The spinal cord is one of the first structures to develop when a sheet of cells on the back of the embryo folds in the middle to form a tube, which will become the spinal cord full of nerves. At one end, the tube enlarges to form the brain's major sections.

The amniotic fluid also begins to accumulate and in the weeks and months ahead this fluid will cushion your precious baby. The placenta, chorionic villi, and the umbilical cord - which delivers nourishment and oxygen to your baby - are already on the job. By the end of the first month, your baby will be about 1/10 of an inch long (smaller than a grain of rice) and its heart, no larger than a poppy seed, will have begun beating.

Learn More: Amniotic Fluid

Join the Discussion: Cord Blood Banking Message Board

How is your body changing this week? Find out: My Pregnant Body Week 4

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