To better understand the changes your body goes through during the last trimester and labor, it is helpful to be familiar with basic anatomy. Open the activity on the right to compare your body before pregnancy to your body at 37 weeks. You'll see how your body adjusts in amazing ways to support your growing baby. Then, play the video to learn about pregnancy anatomy from inside the womb.

open activity Activity: Comparative Anatomy


Comparative Anatomy

Mouse over each word to highlight organs

play video Anatomy: Take a 3D look inside pregnancy.

view text Take a 3D look inside pregnancy.

It’s helpful to understand what’s happening inside your body during the third trimester as it prepares for labor. This animation shows a pregnant woman ready for birth with her full-term baby positioned head-down. Your baby lives inside of your uterus. This is a strong, balloon-shaped muscle that contracts during labor. The bottom part of your uterus is called the cervix. A mucous plug fills the cervix to protect your baby from the outside environment. Your cervix opens into the vagina, or birth canal. It’s through this passageway that your baby enters the world. The placenta is an organ that forms early after conception and grows into the wall of uterus. It makes pregnancy hormones, delivers oxygen and nutrients from you to your baby, and removes waste from your baby’s blood. The umbilical cord allows your baby’s blood to travel to and from the placenta. Growing out from the placenta is the bag of waters, or amniotic sac. The amniotic fluid, inside the sac cushions your baby in a comfortable, warm environment.

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Fetal Development : These amazing 4D ultrasound images show you how babies move in the womb.

Fetal Development
view text These amazing 4D ultrasound images show you how babies move in the womb.

Pregnancy lasts about 40 weeks and is divided into three trimesters. Let’s focus on the third trimester. It starts at week 28 of your pregnancy, and ends with the birth of your baby. During these final weeks, your baby continues to grow and develop. When you are between 39 and 41 weeks, your pregnancy is considered full term and your baby is ready to be born. If you haven’t had your baby by 42 weeks, you are considered postterm, which is also normal but your healthcare provider will probably keep a closer eye on you and your baby.

4D ultrasound images like this one give us a glimpse at what babies can do during the third trimester. As this baby rubs her eyes, you’ll see that she already has her own unique facial features. In this next ultrasound, watch as she licks her arm. These mouth and tongue movements help her learn how to feed. And here, she is practicing how to move her hands and fingers.

While it looks like your baby is ready to greet the world, he needs a little more time. Babies born from the 37th week to the end of the 38th week are considered “early term.” Early-term babies are still at a greater risk for breathing, feeding, and other medical problems. It's usually healthiest for the baby to be born at 39 weeks or later.

During the final trimester of pregnancy, your baby’s brain continues to develop. In fact, it practically doubles in size and adds brain cell connections needed for balance, coordination, and learning. Also, your baby’s lungs are still forming and he is gaining fat that will help him stay warm once he is born.

So, even though you may be uncomfortable, be patient. The health of your baby is worth the wait!

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