Medically Reviewed by Traci C. Johnson, MD on May 09, 2023
Your Pregnancy Stage by Stage

Your Pregnancy Stage by Stage

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Are you curious about what's going on in your uterus during pregnancy? Take a peek inside to see all that's happening with your fetus and your body -- and what to expect as your pregnancy progresses.

Conception 

Conception 

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When a sperm joins with an egg, the two form a single cell called a zygote that contains DNA from both parents. This is fertilization, also called conception. Within about 3 days, the zygote begins dividing into more cells. By about 5-6 days, it has traveled through the fallopian tube into the uterus. At this stage, it's called a blastocyst. It attaches, or implants, to the uterus walls. By day 10-12, the zygote has become an embryo. 

Development at 4 Weeks

Development at 4 Weeks

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At this point, the embryo is developing the structures that will eventually form the face and neck. The heart and blood vessels continue to develop. And the lungs, stomach, and liver start to develop. The placenta, which will nourish the fetus, is forming. A home pregnancy test could show up positive now.

Development at 8 Weeks

Development at 8 Weeks

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The embryo is now a little over half an inch in size. Eyelids and ears are forming, and you can see the tip of the nose. The arms and legs are well formed. The fingers and toes grow longer and more distinct. At the end of the 10th week of pregnancy, the embryo is considered a fetus. That's what doctors call it until birth. 

Development at 12 Weeks

Development at 12 Weeks

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The fetus measures about 2 inches and starts to make its own movements. You may start to feel the top of your uterus above your pubic bone. Your doctor may hear the heartbeat with special instruments. The sex organs should start to become clear. At the end of the 12th week, the first trimester is over.

Development at 16 Weeks

Development at 16 Weeks

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The fetus now measures about 4.3 to 4.6 inches and weighs about 3.5 ounces. You should be able to feel the top of your uterus about 3 inches below your belly button. The fetus' eyes can blink and the heart and blood vessels are fully formed. Its fingers and toes have fingerprints.

Development at 20 Weeks

Development at 20 Weeks

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The fetus weighs about 10 ounces and is a little more than 6 inches long. Your uterus should be at the level of your belly button. The fetus can suck its thumb, yawn, stretch, and make faces. Soon -- if you haven't already -- you'll feel it move, which is called "quickening."

Time for an Ultrasound

Time for an Ultrasound

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An ultrasound is usually done at 20 weeks. During this ultrasound, the doctor will make sure that the placenta is healthy and attached normally and that your fetus is growing properly. You can see the heartbeat and movement of its body, arms, and legs on the ultrasound. You can usually find out whether it's a boy or a girl at 20 weeks.

Shown here is a 2D ultrasound (inset) contrasted with a 4D ultrasound, both at 20 weeks.

Development at 24 Weeks

Development at 24 Weeks

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The fetus weighs about 1.4 pounds now and responds to sounds by moving or increasing their pulse. You may notice jerking motions if they hiccup. With the inner ear fully developed, it may be able to sense being upside down in the womb.

Development at 28 Weeks

Development at 28 Weeks

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The fetus weighs about 2 pounds and 6 ounces and changes position often at this point in pregnancy. If you had to deliver prematurely now, there is a good chance it would survive. Ask your doctor about preterm labor warning signs. With the third trimester beginning, now is the time to register for birthing classes. They prepare you for many aspects of childbirth, including labor and delivery and taking care of your newborn. 

Development at 32 Weeks

Development at 32 Weeks

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The fetus weighs almost 4 pounds and moves often. It has fewer wrinkles as a layer of fat starts to form under the skin. Between now and delivery, your fetus gains up to half its birth weight. Think about how you plan to feed your baby. You may notice a yellowish fluid leaking from your breasts. That's colostrum, and it happens to prepare your breasts for making milk. Most people go to the doctor every 2 weeks at this stage. 

Development at 36 Weeks

Development at 36 Weeks

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A fetus' size depends on things like gender, the parents' size, and whether it's a multiple. On average, it's about 18.5 inches and weighs close to 6 pounds. The brain has been developing rapidly. Lungs are almost fully developed. The head is usually positioned down into the pelvis. A baby is considered early-term if born between 37-39 weeks, at term at 39-40 weeks, and late term at 41-42 weeks.

 

Birth!

Birth!

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Your due date marks the end of your 40th week. The delivery date is calculated using the first day of your last period. Based on this, pregnancy can last between 38 and 42 weeks. Some post-term pregnancies -- those lasting more than 42 weeks -- aren't actually late. The due date may just may not have been accurate. For safety reasons, most babies are delivered by 42 weeks. Sometimes the doctor may need to induce labor to make that happen.