Twin to twin transfusion syndrome (TTTS) is a condition that occurs only in monochorionic pregnancies — ones in which two or more genetically identical babies (usually twins) share the same placenta. Although all identical twins share a placenta, TTTS develops in about 10 to 15 percent of those pregnancies. The condition does not occur when the twins are non-identical (fraternal).
When babies share a placenta they also share connecting blood vessels. Usually the blood flow is equally balanced between them, and the babies are able to grow and develop normally (Figure 1). But in cases of TTTS, the flow of blood becomes unbalanced, and one baby will actually donate blood to the other. When this happens, the baby donating the blood (the “donor” twin) becomes dehydrated and stops making urine. This results in a decrease in amniotic fluid, the protective liquid that surrounds the baby in the womb. The baby receiving the extra blood (the “recipient” twin), however, produces higher-than-normal amounts of urine, resulting in excess amniotic fluid (Figure 2).
Untreated, TTTS can be life-threatening for both babies. The donor twin may experience much slower-than-normal growth, while the recipient twin is at risk of heart failure due to the extra volume of blood. Twin to twin transfusion syndrome treatment is available at Midwest Fetal Care Center.
In some TTTS cases only red blood cells transfer between the babies. In these cases the amniotic fluid levels remain normal. This form of TTTS is known as Twin Anemia Polycythemia Sequence (TAPS). It occurs when the vascular connections between the babies are only tiny blood vessels in the shared placenta, permitting just red blood cells to flow from one baby to the other. Over time, too many red blood cells build up in the recipient twin’s blood, causing the blood to thicken (a condition known as polycythemia). At the same time, the donor twin’s blood will have too few red blood cells (anemia).
At 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 twin to twin transfusion syndrome treatment. That way, you are assured of getting the best possible information by some of the most experienced physicians in the country. For TTTS, your care team will 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.
The placenta is a very active organ and provides babies with oxygen and nutrients during pregnancy. 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. When unborn babies share a placenta, the result can be an imbalance in blood circulation, with one baby receiving too much blood through the umbilical cord and the other receiving too little. It is this imbalance that leads to TTTS.
A twin to twin transfusion syndrome diagnosis is confirmed by ultrasound. The condition becomes evident when the ultrasound images show that one child has extra amniotic fluid and the other child has significantly decreased amounts. Abnormalities in the blood-flow patterns in the umbilical cord may also be found. In addition, the mother may experience a rapid enlargement of her uterus — more quickly than is expected during pregnancy.
Because TTTS can develop rapidly, women carrying twins who share a placenta should undergo frequent ultrasounds to evaluate amniotic fluid volumes. Typically, ultrasounds are performed every two weeks, starting at 16 weeks. The frequency of ultrasounds then increases during the third trimester.
When TTTS is diagnosed, a staging system is used to classify the severity of the condition. This system — known as the Quintero staging system — helps to determine whether an intervention is needed and which treatment option(s) might be most appropriate. Here is an explanation of twin to twin transfusion syndrome stages:
Stage I: The ultrasound shows an imbalance of amniotic fluid around the twins, but the donor twin’s bladder is still visible. The visibility of the bladder indicates the donor baby is receiving enough nutrients and fluid through the blood to produce urine.
Stage II: The ultrasound shows an imbalance of amniotic fluid around the twins, but the donor twin’s bladder is not visible. This finding indicates the bladder is empty — a sign that the baby has stopped making urine.
Stage III: In addition to the Stage I and II indicators, the ultrasound shows significant abnormalities in the flow of blood within the twins’ umbilical cords.
Stage IV: In addition to the Stages I-III indicators, the recipient twin shows signs of heart failure (hydrops fetalis, or extra fluid within the baby).
Our prenatal management of babies with TTTS centers on monitoring the babies frequently with high-resolution fetal ultrasonography and fetal echocardiography. This testing allows us to measure the amount of 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.
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 volume of amniotic fluid that surrounds them throughout the pregnancy.
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 function while in the womb.
The key to twin to twin transfusion syndrome treatment is early diagnosis and intervention. What treatment option will be best for your babies will depend on the stage of the TTTS and your babies’ gestational age at diagnosis. Several options are available, including the following:
95% of procedures resulted in at least one twin surviving
73% of procedures resulted in both twins surviving
Most babies with TTTS are born prematurely, but our goal will be to have your babies delivered as close to your due date as possible. Babies who are treated with laser ablation are typically delivered around week 31 or 32 of the pregnancy.
We will recommend that your babies be born at 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.
The long-term prognosis for babies with TTTS depends on how soon the condition is treated after it has developed, as well as the age of the babies at delivery. The earlier the babies receive treatment and the longer they stay in the womb before birth, the less likely they will experience complications.
When untreated, 90 percent of babies with advanced TTTS do not survive to birth. That percentage is dramatically improved for babies who undergo fetoscopic laser photocoagulation. In almost 90 percent of those pregnancies, at least one baby will survive and be healthy after leaving the hospital NICU. Having both twins survive advanced TTTS remains a challenge, however. Across all medical centers in the United States, about half of pregnancies treated for TTTS end with two healthy babies.
Because of all the potential health issues associated with TTTS, your babies will require long-term follow-up care. At Children’s Minnesota, we have developed a detailed care plan for babies who experienced TTTS during gestation. 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 baby may require to manage any twin to twin transfusion syndrome long term effects.
Need a referral or more information? You or your provider can reach the Midwest Fetal Care Center at 855-693-3825.
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Twin to Twin Transfusion Syndrome: Pathophysiology, diagnosis and up to date management