Twin Ultrasound Images From Every Trimester

Parents partnered with the American Institute of Ultrasound Medicine (AIUM) for a unique peek at twin ultrasound images from each trimester.

Most people may only receive one or two ultrasounds during pregnancy. The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) recommends that twin fetuses receive a first-trimester ultrasound and a second-trimester ultrasound to screen for anomalies. Monochorionic twins (identical twins that share a placenta) should also receive a cardiac screening assessment, which may be more evident in the third trimester.

But Parents partnered with the American Institute of Ultrasound Medicine (AIUM) for a unique peek at twin fetal development in each trimester. These images reveal all the intricate details of their growth from a collection of cells to a full-term newborn. 

Read on to learn about twin fetal development and see some incredible twin ultrasound images from each trimester of pregnancy.

01 of 11

Week 6 (4 Weeks From Conception)

twins ultrasound week 6
American Institute of Ultrasound in Medicine - AIUM.org

Embryonic size: Length measures 1/6 to 1/4 of an inch from crown to rump. Weight is still too small to measure.

Embryonic development milestones: This week, a sonographer can detect embryonic cardiac activity. There are now two distinct amniotic sacs, and the twins' heads, legs, and umbilical cords are forming.

Although this may not look like much, these circles show two distinct gestational sacs—twins! With a single pregnancy, only one sac would appear on the screen. Here, the sonographer (ultrasound technician) has identified each embryo, one marked AA, the other BB.

Most people receive several ultrasounds during a twin pregnancy to ensure that both babies are growing properly and the pregnancy is progressing normally. Your twins will grow at the same rate as singletons until about 26 weeks. Research has found that twins may weigh about 10% less than singletons at term.

02 of 11

Week 11 (9 Weeks From Conception)

twins ultrasound week 11
American Institute of Ultrasound in Medicine - AIUM.org

Fetal size: Length measures 1.61 inches from crown to rump. Weight is just 0.25 ounces.

Fetal development milestones: Little arms and legs are growing and elongating this week! Facial features are developing, as are fingers and toes.

Just 11 weeks into your pregnancy (nine weeks from conception), your babies' faces are becoming more recognizable, with ears and eyes gradually moving into the proper place. Where there were once only small buds, arms and legs are now growing.

In this twin ultrasound image, each fetus has their own amniotic sac and umbilical cord. If your twins are fraternal (dizygotic), they are formed from two separate fertilized eggs and will have separate sacs and cords. However, identical (monozygotic) twins might share an amniotic sac or have separate sacs depending on how early the egg is divided into two.

Here, the sonographer has marked each twin, one with an A and the other with a B. The baby marked A is always the one closest to the cervix. Here, you can see the cervix in the lower right-hand corner of the image as the grayish form that comes near baby A. This baby has their head facing the cervix (notice the white facial bones), while baby B has their back toward the membrane that separates the two babies.

03 of 11

Week 13 (11 Weeks From Conception)

twins ultrasound week 13
American Institute of Ultrasound in Medicine - AIUM.org

Fetal size: Length is almost 3 inches from crown to rump. Weight is almost 1 ounce.

Fetal development milestones: Kidney and urinary tracts are now functioning. Your babies can suck on their thumbs. Genitalia is developing, too.

This 3D twin ultrasound image shows how each baby develops, much like in a single pregnancy. Notice that the babies' heads are more prominent than their growing limbs. Soon, their arms and legs will be proportionated to the rest of their bodies.

With just the right angle, the sonographer may be able to view each baby's developing genitalia. But at this early point in the pregnancy, genitals often look the same and will still be challenging to determine.

04 of 11

Week 14 (12 Weeks From Conception)

twins ultrasound week 14
American Institute of Ultrasound in Medicine - AIUM.org

Fetal size: Length measures 3 1/4 to 4 inches from crown to rump. Weight is around 1 ounce.

Fetal development milestones: Your babies' genitalia continue to form. The tissue under their faces and limbs is beginning to harden into bone. Their livers and spleens produce red blood cells. Upper limbs are becoming proportionate to the rest of their bodies (although lower limbs are still underdeveloped).

Now, into your second trimester, your babies' bones are beginning to harden in an ossification process, where inorganic and organic compounds come together to help the skeleton harden. Looking closely at each baby's head, you can see the ossified white outlines of the bones in the skull.

Baby A has their back toward the right side of the image, so their face is toward the membrane. Their twin, Baby B, has their back to the membrane (notice the white line of balls indicating the spinal column) and their arm to their side.

05 of 11

Week 18 (16 Weeks From Conception)

twins ultrasound week 18
American Institute of Ultrasound in Medicine - AIUM.org

Fetal size: Length is 5 to 5 1/2 inches from crown to rump. Weight is about 5 1/4 ounces.

Fetal development milestones: The babies' senses are beginning to function. Facial features are now in their proper position. Fat tissue is developing. And you may be feeling fetal movement!

Almost halfway into your pregnancy, your babies are more alert. In fact, their ears may even pick up on some sounds. According to the American Academy of Pediatrics (AAP), at 18 weeks, babies can hear sounds inside your body, like your heartbeat.

Your babies' facial features are continuing to become more refined. In this image, Baby B has their back to the right side of the picture. Notice the white grouping, which indicates their spinal column. The dark circular form is their heart, and the faint, bubble-looking form above them is the umbilical cord.

Baby A's umbilical cord is also visible at the top of the baby's body. The membrane that separates the two growing babies can move and sway as the fluid in the uterus moves—or as the babies wiggle. Here, it's swaying toward Baby B.

06 of 11

Week 19 (17 Weeks From Conception)

twins ultrasound week 19
American Institute of Ultrasound in Medicine - AIUM.org

Fetal size: Length is 5 1/4 to 6 inches from crown to rump. Weight is about 7 ounces.

Fetal development milestones: Arms and legs are now well-developed and in proportion. Late in the second trimester, a fetus becomes covered with cheeselike vernix as protection. Fat is beginning to build up, especially around sensitive areas like the neck, sternum, and kidneys.

It's nearly impossible for the sonographer to capture a picture of both your babies' body profiles. In this image, one baby, BB, is positioned with their head nudging the membrane separating the two. The other baby, marked here as AA, looks up and to the left of the image.

You may begin to feel all this movement and heads shifting position. While your babies' arms and legs are now well-developed, their movements will still feel like little more than a flutter. In the coming weeks, their kicks and jabs will become more recognizable—and forceful!

07 of 11

Week 20 (18 Weeks From Conception)

twins ultrasound week 20
American Institute of Ultrasound in Medicine - AIUM.org

Fetal size: Length measures 5 2/3 to 6 1/2 inches from crown to rump. Weight is approximately 9 ounces.

Fetal development milestones: Hair and nails are continuing to grow. If either of your babies has a uterus, it is now formed, and the vaginal canal is forming. You should be able to really feel movement now!

As your babies grow, they have less room to maneuver. In this twin ultrasound image, the babies look as though their heads are touching. Often, the babies' heads will rub together or touch, separated only by the thin membrane that lies between the two.

With this image, the sonographer confirms that, indeed, two babies are developing and also that the babies' heads are about the same size. If one head is significantly larger than the other, the sonographer may make additional measurements to ensure that both babies are developing properly.

Different fetal sizes may indicate a potential problem in the pregnancy called selective intrauterine growth restriction (sIUGR). This condition might indicate a fetal anomaly in one twin or that the umbilical cord isn't functioning correctly.

08 of 11

Week 26 (24 Weeks From Conception)

twins ultrasound week 26
American Institute of Ultrasound in Medicine - AIUM.org

Fetal size: Length is about 9 1/4 inches from crown to rump. Weight is nearly 2 pounds.

Fetal development milestones: Fingernails are fully developed. Eyelashes are forming, and scalp hair continues to grow.

In this twin ultrasound image, you can see how the babies' heads are touching. The hand pointers the sonographer placed on the picture point out the babies' hair.

At this point in development, fetuses have been growing hair on their scalps for some time. While not every baby has hair on their head at birth, these two will have some curly locks!

09 of 11

Week 27 (25 Weeks From Conception)

twins ultrasound week 27
American Institute of Ultrasound in Medicine - AIUM.org

Fetal size: Length is about 9 2/3 inches from crown to rump, and total length is about 15 1/4 inches. Weight is about 2 pounds.

Fetal development milestones: Lungs continue to develop, and your babies' livers are maturing. Their immune systems are also strengthening.

This ultrasound image actually shows triplets! Marked with A, B, and C, this image captures three babies' heads in one image. It's very unusual for wiggly babies in utero to come together so that a sonographer can fit all three into the view screen. Looking at each head, you can see the bright white outline of the ossified, or hardening, skull bones.

As with marking twins in utero, the sonographer tags the baby closest to the cervix with an A, the next closest, B. That will also be the order in which the babies are born.

10 of 11

Week 28 (26 Weeks From Conception)

twins ultrasound week 28
American Institute of Ultrasound in Medicine - AIUM.org

Fetal size: Length measures 10 inches from crown to rump, and total length is 15 3/4 inches. Weight is almost 2 1/2 pounds.

Fetal development milestones: Brain tissue continues to develop, and your babies' scalp hair continues to grow. Your babies are gaining weight and opening their eyes.

At 28 weeks gestation, your babies are beginning to get scrunched in their home inside the uterus. Although you can't see the membrane in this image, a thin wall separates the two babies.

The bright white lines in this twin ultrasound image represent ossified, or hardened, facial bones in each baby's head. You may notice that your babies' movements become more sluggish as they have less wiggle room.

11 of 11

Week 36 (34 Weeks From Conception)

twins ultrasound week 36
American Institute of Ultrasound in Medicine - AIUM.org

Fetal size: Length is about 13 1/2 inches from crown to rump, and total length is about 20 1/4 inches. Weight is 6 pounds.

Fetal development milestones: A big, healthy weight gain! All body systems are now developed and functioning.

Only a few more weeks until delivery day! With a twin pregnancy, you're most likely to receive several ultrasounds to confirm that your babies are developing on schedule.

As you near your babies' due date, your health care provider may request an ultrasound examination to check the babies' position in the uterus. In this twin ultrasound image, the two babies lie cheek to cheek with only a thin membrane separating them.

Editor's Note

The sonographers of the Johns Hopkins Maternal-Fetal Diagnosis and Treatment Center provided all ultrasound images for this slideshow. We are grateful to Christine Bird, BS, RDMS, RVT, chief obstetrical sonographer, and Jude Crino, MD, medical director, for their assistance with this project. For examples of prenatal ultrasounds and more information on your baby's fetal development, be sure to visit www.aium.org.

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Sources
Parents uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. ISUOG Practice Guidelines: role of ultrasound in twin pregnancyUltrasound Obstet Gynecol. 2016.

  2. Differences in fetal growth patterns between twins and singletonsJ Matern Fetal Neonatal Med. 2020.

  3. The differences between identical and fraternal twins. American Academy of Pediatrics. 2019.

  4. When can my unborn baby hear me? I'd love to be able to read and sing to them. American Academy of Pediatrics. 2021.

  5. The second trimester. University of Rochester Medical Center. n.d.

  6. Selective intrauterine growth restriction (sIUGR). C.S. Mott Children's Hospital, University of Michigan Health. n.d.

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