Your Developing Baby: Week 9

What's going on with your baby in pregnancy week nine? Find out all about important pregnancy milestones and exciting fetal development specific to this week of pregnancy!

Week 9 American Institute of Ultrasound in Medicine -

Perhaps the most important development happening this week is taking place in your baby-to-be's heart. While his heart has been beating since week 5, it has been maturing more and more each day. The heart is now divided into four chambers, and the valves that will help funnel blood in and out of the heart are forming. Although your baby's heart is beating, your healthcare provider probably won't be able to pick it up during your prenatal office visits quite yet. Give it another week or so.

The umbilical cord is your baby's lifeline in utero -- connecting Mother and Baby. Made up of three spiraling vessels (one vein and two arteries), the umbilical cord provides oxygenated blood to help your baby ?breathe.? Connected at your baby's abdomen, one vein carries blood to the baby's heart while two arteries carry blood out of baby's heart and back to the placenta. This system of pumping blood in and out of your growing baby's body not only provides oxygen and nutrients, but also removes any waste that your baby produces as he's developing. Along with your baby, the umbilical cord will continue to mature and strengthen to provide everything your baby needs to survive and mature.

The constant blood flow is helping your baby-to-be's limbs develop and lengthen. He already has the beginning of arms, legs, and fingers; this week his toes are also taking shape. Inside those limbs, bones are forming. As those bones develop, joints such as elbows, ankles, shoulders, and wrists are helping your baby move more freely. You won't be able to feel all this movement because your baby-to-be is still so tiny -- even though a sonographer could capture it with an ultrasound.

Another fun note: Baby's eyelids are forming this week!

    Terms to Know

    Vein: A vessel that most often carries deoxygenated blood to the heart in a human's circulatory system. The blood is then oxygenated and sent throughout the body through arteries.

    Artery: A vessel that most often carries oxygenated blood away from the heart in a human's circulatory system. Differs from veins in that vessel walls are often thicker and more muscular.

    Important Information About Your Pregnancy

    Images courtesy of the American Institute of Ultrasound in Medicine (