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What percentage of twin pregnancies are successful?

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 fetal care clinical 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.

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.

Preparing for Multiple Births

A multiple birth is when a mother is pregnant with more than one baby. This may mean a twin pregnancy, triplet pregnancy, or more.

What Are the Types of Multiple Births?

There are two types of twins: monozygotic (identical) and dizygotic (fraternal).

Identical twins result from a single fertilized egg dividing into separate halves and continuing to develop into two separate but identical babies. These twins are genetically identical, with the same chromosomes and similar physical characteristics. They’re the same sex and have the same blood type, hair, and eye color.

Fraternal twins come from two eggs that are fertilized by two separate sperm and are no more alike than other siblings born to the same parents. They may or may not be the same sex. This type of twins is much more common.

«Supertwins» is a common term for triplets and other higher-order multiple births, such as quadruplets or quintuplets. These babies can be identical, fraternal, or a combination of both.

What Are the Risks of Multiple Births?

Risks that can come with carrying multiple babies include:

  • Pre-term (or early) labor resulting in premature births. A typical, single pregnancy lasts about 40 weeks, but a twin pregnancy often lasts between 35 to 37 weeks. More than half of all twins are born prematurely (before 37 weeks), and the risk of premature delivery increases with higher-order multiples.
    Premature babies (preemies) can have health challenges. Their risk increases the earlier they’re born. Because the care of premature babies is so different from that of full-term infants, preemies are usually placed in a neonatal intensive care unit (NICU) after delivery.
  • Other conditions during pregnancy. Preeclampsia, gestational diabetes, placental problems, and fetal growth problems are more likely with multiple pregnancies. Because of this, moms who are pregnant with multiples are followed very closely by their doctor.
  • Long-term problems.Developmental delays and cerebral palsy are more likely as the number of multiples increases.

How Can I Stay Healthy During a Multiple Pregnancy?

Eating properly, getting enough rest, and regular prenatal care are ways for any expectant mother to stay healthy.

It’s important to find health care professionals who have experience with multiple births, and to see your health care provider as he or she recommends. This is so that the doctor can be on the lookout for problems and treat them as needed.

Ask your doctor to recommend a facility that specializes in multiple births. You should be part of a pre-term birth prevention program at your hospital and have immediate access to a specialized NICU should you go into early labor or if one of your babies is born with a health problem.

What Should I Eat if I’m Pregnant With Multiples?

If you’re pregnant with multiples, you should follow general pregnancy nutrition guidelines, including increasing your calcium and folic acid intake.

Another dietary requirement that must be increased if you’re expecting more than one baby is protein. Getting enough protein can help your babies grow properly.

During pregnancy, an increased supply of iron is needed to make enough healthy red blood cells. Low numbers of red blood cells are common in multiple pregnancies. Your doctor will probably prescribe an iron supplement, as your requirement for this mineral usually can’t be met by diet alone. Iron is absorbed more easily when combined with foods that have high amounts of vitamin C, like orange juice.

The doctor will also tell you what vitamins to take to get the nutrients your growing babies need.


How Much Weight Should I Gain if I’m Pregnant With Multiples?

Mothers carrying multiples are expected to gain more weight during pregnancy than mothers carrying a single fetus. But exactly how much weight you should gain depends on your pre-pregnancy weight and the number of fetuses, so make sure to talk to your doctor.

In general, though, you should consume about 300 additional calories a day for each fetus. It might be tough to eat a lot when your abdomen is full of babies, so try to eat smaller, more frequent meals.

How Should I Prepare for Delivery?

Getting ready for a multiple birth may seem overwhelming, especially with concerns about pre-term labor. But know that you have a network of support around you: capable doctors, a caring hospital staff, and a partner, family members, and/or friends.

Discuss the options of vaginal delivery versus cesarean section (C-section) with your doctor well before your due date. Even if you and your doctor agree to attempt a vaginal delivery, things may happen during labor or delivery that make a C-section necessary.

You may choose to have additional birthing attendants in the room during labor and birth. For example, midwives are becoming more common. For multiples, it’s usually recommended that a midwife work with a doctor, rather than alone.

Hiring a doula is another option. Doulas offer support services to women during the birth, as well as after delivery, by assisting with infant care and household chores.

What Will Delivery Be Like?

As labor begins, you’ll be connected to a fetal monitor so your doctor can check each baby’s progress.

If you’re hoping for a vaginal delivery, remember that with multiples this isn’t always possible. Sometimes, a C-section is needed to help keep the babies safe. Most triplets and other higher-order multiples are born by C-section.

If your doctor needs to do a C-section, a catheter will be placed in your bladder, you’ll be given medicine so that you don’t feel pain, and an incision will be made in your abdomen and uterus. The doctor will then deliver your babies through the incision. The babies will be delivered within just a few minutes of each other with this approach. The incision will then be closed.

Many babies born prematurely will need to go immediately to the NICU for the special care they need.

What Else Should I Know?

The first days, weeks, and months are often the most difficult for parents of multiples, as everyone gets used to the frequent feedings, lack of sleep, and lack of personal time.

It can help to join a support group for parents of multiples. Hearing what has worked well for others can help you find solutions to problems you come across.

Enlist whatever help you can — from neighbors, family members, and friends — for household chores and daily tasks. Having extra hands around not only will make feedings easier and help you rest and recover from delivery; it also will give you the precious time you need to get to know your babies.

What factors increase the odds of having twins?


Over the last 30 years, there’s been an increase in the instance of twins. This is primarily because more women are seeking help with getting pregnant. Assistive reproductive technology, things like drugs to increase ovulation and techniques like in vitro fertilization (IVF), increases the risk of having multiple gestations.

Factors that increase the odds of conceiving twins

Age – There’s an increased risk of having twins as women age. The average age at which women get pregnant has increased as more women enter the workforce and start a family a little later. The difficulty of getting pregnant and the percentage of miscarriages also increase as women get older. The number of successful pregnancies in women over 40 isn’t high, but the percentage of those successful pregnancies that result in twins is.

Family history – Twins tend to be more common in some families. There may be an underlying genetic factor that predisposes a woman to release more than one egg at a time, which increases the chance of having twins.

Weight – There has been some consideration that women who are overweight are more likely to have more than one ovulation at a time, which may increase the chance of twins.

Diet – Interestingly, the highest rate of twins in the world is among a particular group in Africa called the Yoruba. One possible reason the twinning rate is so high among the Yoruba is that their diet is rich in a specific kind of yam that contains a phytoestrogen, or plant-like estrogen, that may increase the rate of twinning. In that sense, a woman’s diet may affect the odds of conceiving twins, but I wouldn’t say that any specific diet a woman follows is known to produce twins.

Race – Race may affect the rate of twins. Most statistics show that the lowest rate of twins is in the Asian population, and it’s higher in the Black population. That may be due to dietary factors more than genetics, but it’s hard to say.

All of these factors specifically affect the risk of conceiving fraternal twins. Identical twins occur pretty much at random when an embryo splits after fertilization, so there’s no guaranteed way to increase the odds of having identical twins. That’s is the same across continents, populations and generations.

Jonathan Schaffir is medical director of Obstetrics and Gynecology Outpatient Clinic at The Ohio State University Wexner Medical Center and a professor in the Ohio State College of Medicine.

We have all of your pregnancy and childbirth needs covered at the Ohio State Wexner Medical Center. Find care options

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