Twin Pregnancy Growth Scans: What to Expect at Every Ultrasound
Twin Pregnancy Growth Scans: What to Expect at Every Ultrasound
One of the biggest differences between a singleton pregnancy and a twin pregnancy is the number of ultrasounds you'll have.
After your anatomy scan, you'll likely begin having regular growth scans to make sure both babies are growing well. These ultrasounds are one of the most important ways your healthcare team monitors your twins' health throughout pregnancy.
If you're wondering what all those measurements mean—or why your provider keeps talking about percentiles and estimated weights—you're not alone.
Here's what you can expect at your twin pregnancy growth scans.
What Is a Growth Scan?
A growth scan is an ultrasound that measures how each baby is growing over time.
Unlike your anatomy scan, which focuses on checking that each baby's organs and body structures are developing normally, growth scans are designed to answer questions like:
Are both babies growing appropriately?
Are they growing at a similar rate?
Is each baby receiving enough blood flow and nutrients?
Is there enough amniotic fluid around each baby?
Are there any signs of pregnancy complications?
By comparing today's measurements with previous ultrasounds, your provider can see how your babies are growing throughout pregnancy.
How Often Will I Have Growth Scans?
The exact schedule depends on the type of twins you're carrying and whether your pregnancy has any complications.
In general:
Di/Di twins: Growth scans are often performed about every 4 weeks beginning in the second trimester.
Mo/Di twins: Growth is typically assessed every 2–4 weeks, with additional ultrasounds every 2 weeks to monitor for Twin-to-Twin Transfusion Syndrome (TTTS).
Mo/Mo twins: Monitoring is much more frequent and may include hospitalization later in pregnancy.
If concerns arise about one or both babies, your provider may recommend more frequent ultrasounds.
What Happens During a Growth Scan?
A growth scan is very similar to a regular pregnancy ultrasound.
During the exam, the sonographer will identify each baby and take several measurements before moving on to the next twin.
Your provider may evaluate:
Head circumference
Abdominal circumference
Femur (thigh bone) length
Estimated fetal weight
Amniotic fluid levels
Placenta(s)
Umbilical cord blood flow (when indicated)
Baby's position
The ultrasound usually takes longer than a singleton growth scan because every measurement is repeated for both babies.
How Is My Baby's Weight Estimated?
One of the most anticipated numbers after every growth scan is your babies' estimated weight.
Ultrasound machines use several measurements—including the head, abdomen, and femur—to calculate an Estimated Fetal Weight (EFW).
It's important to remember that this is an estimate, not an exact measurement.
Ultrasound weight estimates become less accurate later in pregnancy because babies are larger and space inside the uterus becomes more limited.
Your provider looks at overall growth trends over time rather than focusing on a single number.
What Are Growth Percentiles?
Growth percentiles compare your baby's estimated size to other babies at the same gestational age.
For example:
A baby in the 50th percentile is close to average.
A baby in the 25th percentile is smaller than average but may still be perfectly healthy.
A baby in the 75th percentile is larger than average.
One twin does not need to be in the same percentile as the other.
Many healthy twins naturally grow at different rates.
Your healthcare provider is usually more interested in consistent growth over time than a single percentile.
What Is Growth Discordance?
Growth discordance describes the size difference between twins.
Some difference is completely normal.
However, if one baby becomes significantly smaller than the other, your provider may recommend additional monitoring to determine whether one baby is experiencing Fetal Growth Restriction (FGR) or another complication.
Monitoring growth discordance helps your healthcare team decide whether your pregnancy can safely continue or whether earlier delivery might become necessary.
Why Does My Provider Measure Amniotic Fluid?
Each baby's amniotic fluid is measured during most growth scans.
Too much or too little fluid can sometimes be an early sign of pregnancy complications.
For twins sharing one placenta, differences in amniotic fluid can also help providers identify conditions such as Twin-to-Twin Transfusion Syndrome (TTTS).
What Are Doppler Studies?
Sometimes your provider may recommend a Doppler ultrasound in addition to a growth scan.
Instead of taking pictures of your babies, Doppler studies measure how blood flows through the umbilical cord and certain fetal blood vessels.
Doppler ultrasounds may be recommended if:
One baby is measuring small
Growth has slowed
FGR is suspected
TTTS or other placental complications are being monitored
These studies provide important information about how well oxygen and nutrients are reaching your babies.
What If One Baby Is Measuring Smaller?
Hearing that one twin is smaller than the other can be scary.
Fortunately, it doesn't automatically mean something is wrong.
Many twins have differences in size and continue to grow well throughout pregnancy.
If one baby begins falling behind, your healthcare provider may recommend:
More frequent growth scans
Doppler ultrasounds
Nonstress Tests (NSTs)
Biophysical Profiles (BPPs)
Additional monitoring by your Maternal-Fetal Medicine specialist
The goal is to carefully balance keeping your babies safely inside the uterus while recognizing if earlier delivery would be the healthier option.
How Accurate Are Growth Scans?
Growth scans are one of the best tools available for monitoring fetal growth, but they aren't perfect.
Because ultrasound estimates are based on measurements—not direct weighing—it's common for babies to weigh several ounces more or less than predicted after birth.
For that reason, providers pay close attention to growth patterns across multiple ultrasounds rather than relying on one scan alone.
My RN & Twin Mom Perspective
As an RN, I understand how valuable growth scans are because they allow providers to monitor babies long before problems become obvious.
As a twin mom, I also remember counting down to every growth scan. Seeing my babies on the screen, hearing their heartbeats, and learning how much they'd grown became some of my favorite appointments.
I also remember feeling nervous every single time, wondering if everything would still be okay. If you're feeling that way too, you're definitely not alone. It's completely normal to feel anxious before these appointments, especially during a high-risk pregnancy.
💛 Twin Mom Tip
Try not to compare your twins' estimated weights with babies you see online or even with other twin pregnancies.
Every pregnancy is different, and every set of twins follows its own growth pattern. The most important comparison is how your babies are growing over time, not how they compare to someone else's.
Frequently Asked Questions
How long does a twin growth scan take?
Most appointments last between 30 and 60 minutes, depending on your babies' positions and whether additional measurements are needed.
Are growth scans safe?
Yes. Ultrasound has been used during pregnancy for decades and is considered safe when performed for medical purposes by trained healthcare professionals.
Will I have a growth scan at every appointment?
Not necessarily. Many routine prenatal visits don't include an ultrasound. Your provider will explain your monitoring schedule based on your pregnancy.
What happens if my twins are measuring differently?
Some size difference is expected. If the difference becomes larger than expected, your provider may recommend more frequent monitoring or additional testing.
Can ultrasound accurately predict birth weight?
Ultrasound provides an estimate of birth weight, but it isn't exact. Most estimates are close, though some babies weigh more or less than predicted.
Related Guides
Twin Pregnancy Ultrasounds: What to Expect Throughout Your Pregnancy
Your Twin Pregnancy Anatomy Scan: What to Expect
What Is a Maternal-Fetal Medicine (MFM) Doctor?
Nonstress Test (NST): What to Expect
Biophysical Profile (BPP): What to Expect
Twin Pregnancy Terms Explained: The Complete A–Z Glossary
Early Signs of Preterm Labor With Twins Every Mom Should Know
References
American College of Obstetricians and Gynecologists (ACOG). Multiple Pregnancy, Ultrasound Exams, and patient education resources.
Society for Maternal-Fetal Medicine (SMFM). Coding for Two: Caring for a Twin Pregnancy and patient education resources.
International Society of Ultrasound in Obstetrics and Gynecology (ISUOG). Practice Guidelines: Role of Ultrasound in Twin Pregnancy.
American Institute of Ultrasound in Medicine (AIUM). Practice Parameter for the Performance of Obstetric Ultrasound Examinations.
Medical Disclaimer
This article is for educational purposes only and should not replace medical advice from your healthcare provider. Always consult your OB, maternal-fetal medicine specialist, or another qualified healthcare professional with questions about your pregnancy, ultrasound results, or any concerning symptoms.
