Selective intrauterine growth restriction

What is selective intrauterine growth restriction (sIUGR)?

Selective intrauterine growth restriction (sIUGR) is a condition that occurs in twin pregnancies when one of the babies does not receive enough nourishment through the placenta to grow at a normal rate. It is diagnosed when the fetal weight of the growth-restricted twin falls below the 10th percentile, and the weight difference between the twins exceeds 20 percent.

sIUGR occurs in 10 percent to 15 percent of dichorionic (ones in which the babies have two separate placentas) and monochorionic twin pregnancies (ones in which the babies share a placenta). Dichorionic twins have entirely separate fetal-placenta blood circulations, and thus the larger twin is unaffected. For the smaller twin, however, the condition can be life threatening. With monochorionic twins, the risks are increased because the twins share blood vessels in the placenta. This means that the larger twin may also be affected if there is an adverse event with the smaller twin.

Even when only one twin is affected, however, both babies are at risk because any necessary intervention for one twin affects the entire pregnancy.

Who will be on my care team?

At the Midwest Fetal Care Center, a collaboration between Children’s Minnesota and Allina Health, we specialize in individual attention that starts with you having your own personal care coordinator to help you navigate the complex process of caring for your babies. We use a comprehensive team approach to sIUGR. That way, you are assured of getting the best possible information by some of the most experienced physicians in the country. For sIUGR, your care team may include a maternal-fetal specialist, a fetal interventionist, a pediatric cardiologist, a neonatologist, a nurse specialist care coordinator, a perinatal social worker and several other technical specialists. This entire team will follow you and your babies closely through the evaluation process, and the team will be responsible for designing and carrying out your complete care plan.

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What causes selective intrauterine growth restriction (sIUGR)?

The placenta, which provides the babies with oxygen and nutrients during gestation, is a very active organ. It grows along with the babies. Sometimes, for reasons that are not well understood, the normal flow of blood in the placenta’s blood vessels develops an abnormal pattern, or the placenta is shared unequally between twins.

The cause of sIUGR is different for dichorionic and monochorionic twins. In dichorionic twins, the condition is associated with placental insufficiency, which is the failure of the placenta to deliver an adequate amount of nutrients and oxygen to the affected twin. Fortunately, the circulatory systems of dichorionic twins are independent of each other, and the larger twin remains unaffected.

In monochorionic twins, sIUGR occurs when one baby receives a significantly smaller portion of the blood supply from the shared placenta and, thus, fewer nutrients. Over time, this lack of nourishment results in the baby growing at a much slower-than-normal rate. In addition, the placenta contains blood vessels that are shared between the twins. These shared vessels often include large connections (known as arterio-arterial anastomoses). The smaller twin may benefit from the connections, as they allow the larger twin to “share” some blood flow. This compensatory effect can help the smaller twin survive for many weeks. As the pregnancy progresses, however, the shared vessels leave the larger twin vulnerable to sudden changes in the smaller twin’s blood circulation. If the smaller twin does not survive, the larger twin may be at risk.

How is selective intrauterine growth restriction (sIUGR) diagnosed?

sIUGR is diagnosed by ultrasound as early as the 16th to 18th week of pregnancy. The condition is identified when the estimated weight of one twin falls below the 10th percentile and the weight difference between the twins exceeds 20 percent. The ultrasound may also find abnormalities in blood flow patterns within the umbilical cord.

In monochorionic twins, it is important to distinguish sIUGR from twin to twin transfusion syndrome (TTTS). TTTS and sIUGR both involve an abnormally shared placenta, but are differentiated by how much of the placenta is being shared and the types of blood vessel connections between the twins. Our experienced team uses detailed ultrasound evaluations to distinguish between TTTS and sIUGR.

What are the types of selective intrauterine growth restriction (sIUGR) in monochorionic twins?

When sIUGR is diagnosed, a system is used to classify the severity of the condition. This system — known as the Gratacos classification system — helps to determine whether an intervention is needed and which treatment option(s) might be most appropriate.

The three types of sIUGR are classified based on the blood-flow pattern (wave form) in the umbilical artery of the growth-restricted twin. Here is an explanation of the various types:

Type 1: The ultrasound shows a positive end-diastolic flow — or persistent forward flow — in the umbilical artery of the growth-restricted twin. Babies with type 1 sIUGR have a good prognosis and are born, on average, during the 34th or 35th week of pregnancy. In most cases of type 1 sIUGR, the babies’ condition remains stable throughout the pregnancy, although in up to 15 percent of cases, the sIUGR progresses as the pregnancy continues. The overall survival rate for babies with type 1 sIUGR is greater than 90 percent.

Type 2: The ultrasound shows absent or reversed end-diastolic flow in the umbilical artery of the growth-restricted twin. In other words, the blood flow is either persistently absent in the artery or persistently flowing in a reverse direction, away from the smaller twin. Babies with type 2 sIUGR have a guarded prognosis. About 90 percent of cases worsen as the pregnancy continues. Extreme preterm delivery is common among babies with type 2 sIUGR, often before the 30th week of pregnancy. Internationally, about 50 percent of babies with sIUGR survive, and about 35 percent survive without disabilities.

Type 3: The ultrasound shows intermittent absent or reversed end-diastolic flow  — with some forward flow — in the umbilical artery of the growth-restricted twin. In other words, only occasionally is the blood flow in the artery absent or flowing in a reverse direction. This type of blood-flow pattern is unique to monochorionic twins with sIUGR. It occurs when large arterio-arterial connections are present, allowing shared blood to flow back and forth between the twins. Whether or not the condition will change or worsen during pregnancy is difficult to predict from the ultrasound images. Babies with type 3 sIUGR are born, on average, during the 30th to 32nd week of pregnancy. Their overall survival rate is 80 percent.

How is selective intrauterine growth restriction (sIUGR) managed before birth?

Our prenatal management of babies with sIUGR centers on monitoring the babies frequently with high-resolution ultrasonography. A fetal echocardiogram may also be performed. These tests allows us to measure the amount of growth and amniotic fluid around your babies. It also allows us to assess how well blood is flowing within your babies’ umbilical cords, as well as within other blood vessels.

What is high-resolution fetal ultrasonography?

High-resolution fetal ultrasonography is a non-invasive test performed by one of our ultrasound specialists. The test uses reflected sound waves to create images of your babies within the womb. We will use ultrasonography to follow the development of your babies’ internal organs and overall growth, as well as the blood flow through the umbilical cords throughout the pregnancy.

What is fetal echocardiogram?

Fetal echocardiography (“echo” for short) is performed at our center by a pediatric cardiologist (a physician who specializes in fetal heart abnormalities). This non-invasive, high-resolution ultrasound procedure looks specifically at how your babies’ hearts are structured and how they function while in the womb.

How can selective intrauterine growth restriction (sIUGR) be treated before birth?

The key to treating sIUGR is early diagnosis, close ultrasound surveillance, and, possibly, prenatal intervention. What treatment option will be best for your babies will depend on their chorionicity (dichorionic or monochorionic), their gestational age, and the type of sIUGR identified by the ultrasound.

Treatment options include the following:

  • Expectant management: This involves continued close ultrasound surveillance throughout the pregnancy. We currently recommend expectant management for most Type 1 sIUGR and dichorionic twins.
  • Selective cord occlusion: This procedure may be offered if you have monochorionic twins with Type 2 or Type 3 sIUGR. Selective cord occlusion is a minimally invasive procedure that stops blood flow to the growth-restricted twin. The goal is to optimize the outcome for the normally growing twin. The procedure can be performed using bipolar cord coagulation, interstitial laser, or microwave ablation.
  • Fetoscopic laser photocoagulation: In select cases this minimally invasive surgery can be used to laser ablate (seal) blood vessels that are shared between the babies. Similar to selective cord occlusion, the goal of therapy is to optimize the outcome for the normally growing twin.
  • Delivery: If sIUGR is discovered later in the pregnancy or the condition progresses after the pregnancy reaches its 24th to 26th week, delivery of the babies may be the best option.

How is selective intrauterine growth restriction (sIUGR) treated after birth?

Most babies with sIUGR are born prematurely, but our goal will be to prolong your pregnancy for as long as possible.

We will recommend that your babies are born at a hospital able to care for premature babies, such as one of our specialized Mother Baby Centers. Children’s Minnesota is one of only a few centers nationwide with the birth center located within the hospital complex. This means that your babies will be born just a few feet down the hall from our newborn intensive care unit (NICU). If necessary, many of the physicians you have already met may be present during or immediately after your babies’ birth so we can care for them right away.

What is my baby’s long-term prognosis?

The long-term prognosis for babies with sIUGR depends on the chorionicity of the twin pregnancy, the severity of the condition, whether an intervention was used, and the age of the babies at delivery. The longer the babies stay in the womb before birth, the less likely they will experience complications. In some cases, concerns with neurologic development are present regardless of the babies’ gestational age at birth.

Will my baby require long-term follow-up?

Because of all the potential health issues associated with sIUGR, your babies will require long-term follow-up care. At Children’s Minnesota, we have developed a detailed care plan for babies who experienced sIUGR during pregnancy. Your babies’ plan will be implemented by a comprehensive team of specialists, including a pediatrician (who will coordinate your babies’ overall care), a pediatric cardiologist, a developmental specialist, and any other caregiver your babies may require.

Contact us

Need a referral or more information? You or your provider can reach the Midwest Fetal Care Center at 855-693-3825.