Twins in the Womb Week by Week: A Guide for Expecting Parents

Learning you’re expecting twins can bring excitement, and lots of questions. How do twins grow? Will you feel different from someone carrying one baby? What should you expect during delivery?

Twin pregnancies are unique and can come with a few extra steps along the way. This guide breaks down how twins grow and what to expect each week, so you can feel more confident as you prepare for life with two little ones.

Understanding Twin Pregnancy

There are two ways twins can form. Identical twins come from one fertilized egg that splits into two embryos. These twins share the same DNA, so they’re always the same gender and often look alike.

Fraternal twins happen when two separate eggs are fertilized by two separate sperm. These babies are like regular siblings, just born at the same time. They can be the same gender or different and may not look alike.

No matter how they form, both types of twins go through the same stages of growth—developing organs, limbs, brains, and their own unique personalities.

What to Expect with Identical Twins

Identical twins begin as one egg that splits early in pregnancy. They often share a placenta, the organ that delivers oxygen and nutrients. Some share the same amniotic sac, while others have separate sacs. Each baby always has their own umbilical cord.

If your babies share a sac, your care team may monitor you more closely, since it can raise the chance of cord problems or uneven growth.

Common Symptoms in Twin Pregnancy

Early pregnancy symptoms may feel stronger or start sooner when carrying twins. You might notice:

• More intense nausea (morning sickness)
• Extreme tiredness
• Breast tenderness
• Faster weight gain
• Feeling “more pregnant” earlier

Your body is doing double the work. Get plenty of rest, eat well, and let your care team know how you’re feeling.

Twin Pregnancy Development Week by Week

First Trimester:

You’ll likely confirm your pregnancy with a home test. An early ultrasound (around six to nine weeks) can show if you’re having twins and whether they’re identical or fraternal. This scan also helps determine if your babies share a placenta or sac, which affects your care plan.

By the end of the first trimester, both babies are forming major organs, with tiny hearts beating. They’re about the size of limes.

Second Trimester (Weeks 13–26):

Between 18 and 22 weeks, you’ll have a detailed anatomy scan. This checks the development of both babies, head to toe, including the brain, heart, spine, and other organs. Your doctor will make sure both twins are growing well and developing on track.

Third Trimester (Weeks 27–40):

Your belly will grow quickly, and you may feel more discomfort. Back pain, swelling, shortness of breath, and trouble sleeping are all common. Your care team will monitor you more closely to prepare for a safe delivery.

Weekly Monitoring Guide for Twin Development

Your doctor will likely schedule more frequent ultrasounds during a twin pregnancy, depending on the type of twin pregnancy, to keep an eye on each baby’s progress.

• Weeks 5–6: First ultrasound confirms twins and checks if they are identical or fraternal.
• Weeks 8–12: Regular ultrasounds track heartbeats, limbs, and organ development.
• Weeks 16–20: The anatomy scan checks for growth and rules out potential problems.
• Weeks 24–28: Focus shifts to lungs, brain, and other vital systems.
• Weeks 32–36: Ultrasounds measure size and weight to ensure both babies are growing as they should.
• Weeks 37–40: Final scans monitor movement, position, and readiness for birth.

Regular monitoring helps catch issues early, keeping both you and your babies safe.

Possible Complications with Twins

While many twin pregnancies go smoothly, they are considered higher risk. This doesn’t mean something will go wrong. It just means your doctor will keep a closer watch.
Common complications include:

• Preterm labor (before 37 weeks)
• Premature birth
• Cesarean delivery (C-section)
• Gestational diabetes or high blood pressure
• Postpartum complications like heavier bleeding or longer recovery
• Twin-to-twin transfusion syndrome in case of twins with one placenta

Staying on top of appointments and following your provider’s advice can help reduce risks and lead to a healthy delivery.

Monitoring Twin Pregnancy: What to Expect

You’ll likely have more ultrasounds than someone carrying one baby. Along with early and mid-pregnancy scans, some twins—especially those who share a placenta (monochorionic), may need extra tests like fetal echocardiograms to check their hearts.

Experts recommend all twin pregnancies receive detailed ultrasounds in the first and second trimesters.

Getting Ready for Delivery

Your doctor will look at several things to decide the safest way to deliver:

• The type of twins (identical or fraternal)
• Baby positions (head-down, breech, etc.)
• How far along you are
• Each baby’s size and your overall health

Monochorionic-monoamniotic twins (sharing both a placenta and a sac) are usually delivered by C-section to prevent cord-related complications.

Keep in close contact with your care team and ask questions along the way. Your delivery plan might shift depending on how your pregnancy progresses.

Caring for Newborn Twins

Bringing home two babies is a big job, but also full of love. In those first few weeks, having a plan helps:

• Create a feeding and diaper change schedule
• Take turns with a partner or support person
• Ask family or friends for help
• Connect with other twin parents for support

Breastfeeding twins is possible, though it may take some practice. A lactation consultant can help you find a comfortable routine that works for your family.

You may also want to stock up on extra clothes, bottles, diapers, and safe sleep spaces before the babies arrive.

Twin pregnancy can feel overwhelming at times, but you’re not alone. With good care, trusted support, and the right information, you can move through each week with confidence. This journey may look different, but it’s just as beautiful.

If you ever have questions or concerns, reach out to your care team. They’re here to support you every step of the way.

Welcoming Your Two Little Miracles

Expecting twins is a special journey, full of joy and unique moments. While it can bring extra challenges, many moms go on to have healthy deliveries with the right care and support.

Understanding how twins grow week by week can help you feel more prepared and confident. Regular checkups, ultrasounds and close monitoring help your care team spot any issues early so they can act quickly.

As your due date gets closer, think about making a birth plan. It’s a helpful way to share your wishes with your doctor and feel more ready for delivery day.

If you still need an OB-GYN or want to talk to someone about your pregnancy, our team is here for you. You can request an appointment anytime. We’re happy to help.

Every twin pregnancy is different. Your doctor is your best partner in keeping you and your babies healthy. Keep asking questions, take care of yourself and remember, you’re not alone on this amazing journey.