Complications with twins & higher order multiples

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Some types of conditions specifically affect some twins, triplets and higher order multiples as they develop in the womb. At the Center for Fetal Care, our high-risk pregnancy specialists have training and expertise in the newest, safest treatments for higher order multiples.

Our center was the first in Illinois with the fetal surgery capacity to manage prenatal needs and complications for all higher order multiples pregnancies. We specialize in nonsurgical care, open fetal surgery and minimally invasive procedures. We coordinate care with pediatric experts across Advocate Children’s Hospital to support you and your babies throughout pregnancy, delivery and into childhood.

How do twins develop?

Twins can be identical or fraternal, with each type forming differently:

Identical twins happen when a single sperm fertilizes a single egg, and the fertilized egg (zygote) then divides into two identical embryos. Identical twins share the same genes.
Fraternal twins occur when two separate sperm fertilize two separate eggs. Fraternal twins don’t share the same genes – they’re like siblings from different pregnancies.

What are the different types of twins?

Beyond identical and fraternal, twins have other characteristics that can affect how they develop before birth. A baby in a single pregnancy has one placenta (organ in the womb for nourishment) and one amniotic sac (protective, fluid-filled membrane). In a twin pregnancy, the two babies often share a placenta and sometimes can share an amniotic sac:

Dichorionic twins: Each twin has its own placenta and amniotic sac. All fraternal twins are dichorionic but only about 30% of identical twins.
Monochorionic twins: The babies share a placenta, a feature in about 70% of pregnancies with identical twins. They may or may not share an amniotic sac:
- Monochorionic-diamniotic twins: In these identical twin pairs who share a placenta, each baby has their own amniotic sac. This arrangement is by far the most common.
- Monochorionic-monoamniotic twins: Only about 1% of identical twins share a placenta and an amniotic sac.

How does sharing a placenta affect identical twins?

With monochorionic twins, each baby’s umbilical cord connects to the same placenta. Where the cords do so can affect the baby’s share of resources. Blood vessels also develop in the placenta to supply the babies with nutrients and oxygen. It’s natural for the twins to share some of the blood vessels, and blood can flow back and forth between them.

In most pregnancies with monochorionic twins, the blood supply and placenta are roughly equal between babies. In some cases, an unequal share can increase the risk of complications for the twins.

Types of fetal conditions that affect twins

Monochorionic twins can have a higher risk of certain conditions than dichorionic twins and single babies. These conditions can threaten the life of a twin (or both) when the placenta is shared, making the right care critical.

Some identical twins develop with connected body parts. They can join at the head, chest, abdomen (belly) and other areas.

We can usually find out about these types of twins through ultrasound toward the end of the first trimester. It helps to learn early in your pregnancy because there may be complications. It also gives more time to plan for delivery and evaluate what body parts are shared between the twins.

After delivery, we carefully evaluate conjoined twins and work closely with you to decide on the next steps. Separation surgery may provide an option, depending on the twins’ health, where they connect, and which organs and body parts they share.

In some identical twins, one baby develops congenital conditions, but the other does not. Discordant anomalies refer to structural problems that can affect many organs and body systems. These systems include the heart, lungs, kidneys, intestines and central nervous system (brain, spine and nerves).

Some monochorionic twins develop unevenly, with their estimated weights differing by 20% or more. This variation happens because of unequal placenta and blood sharing.

IUGR is a more severe form of unequal placenta sharing between monochorionic twins. The smaller twin’s estimated fetal weight is below the 10th percentile, or the twins’ weights may differ by 25% or more.

One twin has too few red blood cells (anemia), and the other twin has too many red blood cells, leading to thick blood. TAPS can prevent both babies from receiving enough oxygen.

TRAP occurs in monochorionic twins, when one twin doesn’t fully develop. This twin, called an acardiac twin, may have a missing or poorly developed heart, head or limbs and won’t survive after birth. The other twin, called the pump twin, supplies blood for both twins, straining its heart. The larger the acardiac twin grows, the higher the risk of heart failure in the pump twin.

In some monochorionic twins and higher order multiples, abnormal vascular connections between the twins within the placenta cause differences in blood flow to each baby.

The donor twin loses too much blood, which reduces its nourishment, growth and urine production. Less fetal urine means less fluid in its amniotic sac.
The recipient twin receives too much blood, which increases its growth and urine production, leading to excess amniotic fluid.

In about 10 to 15% of these cases, TTTS will develop. TTTS can affect both babies’ heart function, putting them at risk of heart failure. Learn more about surgery for twin-to-twin transfusion syndrome (TTTS).

Because they share one amniotic sac, monochorionic-monoamniotic twins are more likely to get their umbilical cords tangled. The umbilical cord is the lifeline for your babies, with blood vessels that carry oxygen and nutrients from the placenta. As the twins move in the womb, the cords can become tangled and compressed, potentially reducing or cutting off blood flow.

What causes fetal conditions in twins?

The causes of fetal conditions in twins vary depending on the disorder, with not all causes known or fully understood. Some possible causes and risk factors include:

Problems with cell division in the first few days after a sperm fertilizes an egg
Location of umbilical cord connection with the placenta
Problems with the placenta
Certain health problems in the mother, such as diabetes, high blood pressure or infections

Symptoms and signs of fetal conditions in twins and higher order multiples

Our fetal specialists diagnose twin and higher order multiple pregnancies through ultrasound, and we evaluate the babies for:

Differences between amniotic sacs, including their sizes and amounts of fluid
Differences in the babies’ sizes and estimated weights
Problems with blood flow in the babies, umbilical cords or placenta
Signs of strain on the babies’ hearts, such as fluid buildup

Sometimes, these conditions cause symptoms that you may experience, such as:

Enlarged uterus because of excess amniotic fluid
Feeling of rapid growth in the uterus
Less movement of the babies
Pain, pressure or contractions in the belly
Swelling in the hands, legs and feet during early pregnancy

Diagnosis of fetal conditions in twins and higher order multiples

In routine checkups during your first trimester, your doctor can detect whether you’re carrying twins or a higher order multiple pregnancy. If so, we perform further imaging to see whether the babies are sharing a placenta, an amniotic sac or both.

Knowing whether you have monochorionic twins helps guide our care for you and your babies through pregnancy and delivery. For monochorionic twins, our fetal care specialists see you every two weeks to check your health and your babies’ health. We also refer you to our genetics program for a consultation and evaluation.

We use the latest imaging to monitor you and confirm a possible diagnosis. Our state-of-the-art scans include:

Targeted, high-resolution fetal ultrasound: We check your twins’ growth and development and look for any problems.
Fetal Doppler ultrasound: We assess blood vessels and blood flow from the placenta through the umbilical cords to your babies.
Fetal echocardiogram: Heart ultrasound can show how well your babies’ hearts are working.
Ultrafast fetal MRI: These scans show details of your babies’ internal structures.

Treatment of fetal conditions in twins

Our experienced fetal care and high-risk pregnancy specialists offer comprehensive treatment for twins and higher order multiples, including surgical and nonsurgical options. They provide expert care to help your babies have a successful start in life.

Learn more about our fetal surgery and the nonsurgical treatment and services we offer.