Fetofetal transfusion, more commonly known as “Twin to Twin Transfusion Syndrome” (TTTS), is a very serious prenatal complication. According to the Twin to Twin Transfusion Syndrome Foundation (TTTSF), TTTS occurs in up to 15 percent of pregnancies in which the mother is carrying identical twins that share a placenta. That means that the risk of having TTTS in any given pregnancy is one in 1,000.
If your twins suffer from TTTS, one baby will receive too much blood and the other will receive too little. This is due to imbalanced blood vessel connections between the placenta and the twins.
Twin to Twin Transfusion Syndrome occurs when blood is not equally exchanged between both twins.
In some pregnancies with twins, each fetus is connected to the placenta through its umbilical cord. Blood vessels spread from each cord into the placenta. Each twin sends blood through these vessels into the placenta. They then receive blood through the veins that has been enriched with oxygen and nutrients. Circulation is balanced—each twin sends and receives blood the same way. Although rare, this situation can be healthy, and is called “monochorionic twins.”
In pregnancies affected by TTTS, one twin (the donor) sends blood through the arteries to the placenta, but does not receive enough blood back through the veins. The other twin (the recipient) gets more blood through the veins than what was sent to the placenta through the arteries. This is dangerous for both twins. The donor is often small in size and deprived of nutrients and oxygen. The recipient has an overloaded cardiovascular system, which may lead to poor heart function.
Most cases of TTTS result from abnormalities of the blood vessels in the placenta. Beyond this, specific causes are often unknown.
Pregnancies with multiple fetuses and one placenta carry an elevated risk of TTTS. This type of pregnancy is usually identified during an early ultrasound. You will need to have frequent scans during pregnancy to monitor the size and condition of your twins. According to the Twin to Twin Transfusion Syndrome Foundation, research suggests there may be links between maternal nutrition and TTTS (TTTS Foundation). If you have a high-risk pregnancy, your doctor may recommend a specific diet, or prescribe vitamins.
TTTS is usually identified through ultrasounds and prenatal testing before you feel anything more than typical symptoms of pregnancy. When TTTS has progressed, you may experience “maternal mirror syndrome.” This is when your symptoms mimic those of the recipient fetus who has increased cardiovascular activity. You may experience any of the following:
- severe swelling
- high blood pressure
Maternal mirror syndrome is rare but serious. Seek medical care if your pregnancy is affected by TTTS and you have any of these symptoms. You may be admitted to the hospital to control your symptoms and monitor your twins.
Scheduling and keeping regular prenatal appointments is essential to identifying TTTS. Your doctor will usually be able to identify multiples in the first trimester through ultrasound or fetal heart tones. Once your doctor suspects twins, he or she will examine the fetuses by ultrasound. If both twins share one placenta, your pregnancy will be considered high risk. You will need to undergo regular scans and prenatal testing.
TTTS is often diagnosed by ultrasound based on the levels of amniotic fluid surrounding each twin. In response to lack of oxygen and nutrition, the donor twin’s kidneys may shut down, resulting in limited amniotic fluid. The recipient twin increases urine output to keep up with the extra amount of blood pumping through his or her system, causing high levels of fluid in the amniotic sac.
Another sign of TTTS is the difference in the sizes of the fetuses. This is a less reliable way of diagnosing the condition. One twin being larger than the other may be normal, or could be caused by other types of complications.
Prenatal testing such as amniocentesis may be used to confirm a diagnosis of TTTS.
Treatment varies depending on the severity of TTTS and the health of the mother and babies. Your goal will be to carry the fetuses until they can be delivered safely, at which point TTTS is usually not a threat (although there may be complications from pre-term delivery). The health of the fetuses will be tracked using ultrasound. Fetal MRIs and echocardiograms will assess any problems with the babies’ hearts and brains.
You will likely be told to remain on bed rest through the duration of your pregnancy. Nutritional supplements will also be prescribed.
In severe cases, or if delivery is going to happen soon, you may be hospitalized. A minimally invasive laser procedure may be used to interrupt circulation through the placenta. This surgery is usually ordered only when one or both twins are in immediate danger because it carries some risk of injury to the fetuses.
Once your twins are developed to the point where they may be able to survive outside the womb, you and your doctor will need to plan your delivery. Your doctor may recommend inducing labor or a C-section if it looks like the risks associated with pre-term delivery are not as threatening as the TTTS.
If left untreated, the outlook for twins with TTTS is poor. According to an article in BJOG, An International Journal of Obstetrics and Gynaecology 70 to 80 percent of affected twins will not make it to delivery, and many of those who do survive will have damaged brains, hearts, and kidneys (Ong et al., 2006).
Modern advances in medicine give twins affected by TTTS a more positive outlook. Many mild cases of TTTS can be controlled with bed rest and nutritional therapy until delivery is safe.
Laser surgery for severe cases of TTTS carries some risks, and the outcomes vary greatly. A study in The Journal of Fetal Neonatal Medicine found that survival for one or both twins was 91 percent, and dual survival was 72 percent (Chmait).
There are other treatments for TTTS, such as amnioreduction, in which some of the amniotic fluid is removed from the sac of the larger twin. Another procedure, called a septostomy, makes little holes in the membrane that separates the twins. Neither of these procedures fixes the cause of TTTS the way laser surgery does. Each procedure has its risks.
Many cases of TTTS can’t be prevented. However, maintaining a healthy diet before and during pregnancy may prevent TTTS, or make it less severe if it does occur. Take prenatal supplements as recommended by your doctor. Always attend regular prenatal appointments to monitor your pregnancy. Incidents of TTTS have more positive outcomes when they are identified early and monitored by doctors. TTTS and its treatment is a very complicated medical condition. Consult with your doctor early in your pregnancy to plan out an approach to treating the disorder.