What is Twin to Twin Transfusion Syndrome (TTTS)?
Twin to Twin Transfusion Syndrome (TTTS) is a condition that occurs in identical twin (monozygotic) fetuses that share the same placenta. Monochorionic (one placenta) twin pregnancies have 15% to 20% chances of developing this syndrome. Also known as Twin Oligohydramnios-Polyhydramnios Sequence (TOPS) or Feto-Fetal Transfusion Syndrome (FFTS), it is characterized by imbalances in the flow of blood from one twin to the other due to abnormally connected blood vessels coming from the twins’ placenta. This leads to serious health implications in twins. Once thought to be a rare syndrome, Twin to Twin Transfusion Syndrome (TTTS) is now common, seen 1 in 1000 pregnancies.
In Twin Oligohydramnios-Polyhydramnios Sequence (TOPS), one baby known as donor twin receives less than required amount of blood that in turn reduces the baby size and makes it anemic. The second baby known as the recipient receives more than the required amount of blood that overloads its cardiovascular system and the baby appears large.
The Recepient Twin:
In order to decrease the volume of blood in its body, the recipient twin increases its quantity of urine. To meet this need, the bladder size increases. Also, the heart has to work harder to pump the excess blood, which may lead to heart failure. This twin may also retain fluid, a condition called edema that can lead to defects in digestive or respiratory system and brain. During an ultrasound the large size of the bladder and excess amniotic fluid can be found around the recipient twin’s body. This excess amniotic fluid is called polyhydramnios which makes the mother appear heavier giving an impression of nearing her delivery. The extra fluid not only makes the mother uncomfortable but also may lead to early delivery due to ruptured membranes in the cervical region.
The Donor Twin:
The donor twin makes less than the normal amount of urine and the amniotic fluid around this twin is either very less or totally absent. This lack of amniotic fluid is called oligohydramnios. Eventually the production of urine by the donor twin decreases to an extent that its urinary bladder may not be visible on ultrasound. This twin gets wrapped in its amniotic sac appearing as though its body is stuck up against the uterine wall. Although the donor baby appears small, if he/she survives birth, they have a healthy and strong heart among both because it did not have to work as hard as the recipient’s heart.
Warning Signals/ Diagnosis:
An ultrasound evaluation can diagnose Twin to Twin Transfusion Syndrome. The volume of amniotic fluid is measured by determining the deepest pocket measurement from the mother’s skin to her back. This measurement is called maximum vertical pocket (MVP).
Warning signals in the mother include:
- Sudden increase in body weight.
- A uterus that measures larger than the expected size for that particular month.
- Sensation of a rapidly growing womb.
- Swollen hands and legs in early stages of pregnancy.
- Uterine contractions or tightness and/or pain in the abdomen.
Warning Signals in Twins that appear on ultrasound:
- Single placenta.
- Twins with same sex.
- Evidence of a shared placenta.
- A very thin, almost invisible dividing membrane.
- Difference in sizes of the twins.
- Oligohydramnios in the sac of one twin.
- Polyhydramnios in the sac of the other baby.
- Water in the body of one twin due to heart failure also known as hydrops fetalis.
Stages of TTTS:
Five stages of this syndrome have been proposed based on ultrasound findings.
Stage I – This is the very first stage in which TTTS is observed on ultrasound. Polyhydramnios in the recipient’s amniotic sac with an MVP of 8 centimeters or more and oligohydramnios in the donor’s sac with a maximum vertical pocket (MVP) of 2 centimeters or less is observed. Donor twin’s bladder is still visible.
Stage II – Both oligohydramnios and polyhydramnios are seen but the bladder of the donor twin is not visible during ultrasound evaluation.
Stage III – Doppler is a special type of ultrasound that detects the flow of blood in fetus. The study of blood flow in the fetal ductus venosus (the fetal blood vessel that carries the blood from placenta to heart) and umbilical cord reveals abnormalities in this stage.
Stage IV – In this stage, one or both the twins show accumulation of fluids leading to scalp edema (swollen skin around the head), ascites (excess abdominal fluid), pleural effusions (excess fluid around the lungs) or pericardial effusion (excess fluid around heart). These conditions indicate heart failure and are usually seen in recipient baby.
Stage V – One or both the twins have died. Poor survival is seen in cases that progress to a higher stage over a period of time. According to an estimate, nearly half of the patients progress to next stage, 20% will move to a lower stage and 30% will remain at the same stage.
Treating Twin to Twin Transfusion Syndrome (TTTS):
Several treatment techniques are available depending on the gestational age of the pregnancy, ultrasound results and exact condition of the twins.
If one twin dies, the other faces a risk of damage to the main organs or even death. Even if the second twin survives, a risk of 40% brain damage cannot be ruled out. Moreover, almost 70% to 80% of twins with TTTS die if no treatment is given prior to 2 months of pregnancy (24 weeks gestation).
The treatment options currently available are as follows:
- Amnioreduction – This is a process of draining excess amniotic fluid from the amniotic sac of the recipient baby. The technique usually gets completed in an hour. The amount of fluid removed may vary. About 2.5 liters of fluid is extracted to return the amniotic fluid to its normal level. Soon after the removal of excess fluid, space is created for the smaller twin and the larger twin gets stabilized. Moreover, discomfort associated with carrying the fluid is eased and the risk of premature labor is greatly reduced. This fluid draining process may have to be done more than once. 44% of pregnancies produce both live twins whereas 66% of them produce only one live baby after amnioreduction.
- Fetoscopic Laser – All TTTS patients in stages II, III or IV and a few patients in stage I may be treated with this option. The fetal laser technique involves the introduction of a fiber-optic scope into the amniotic sac of the recipient baby through the wall of the uterus. The abnormal blood vessel connections between the twins can be identified and removed by hitting a laser beam at them. Through this procedure, only the imbalanced blood vessels that travel from one baby to the other are coagulated. The normal blood vessels remain intact to carry the required nutrients.
- Septostomy – This procedure is either performed in combination with amnioreduction or individually. Also called microseptostomy, it involves the insertion of a needle into the membrane between the twins’ amniotic sac to create a hole. This shifts the excess fluid from the recipient twin sac to the donor baby’s amniotic sac. The needle used in this process is the one used in performing amniocentesis (removal of amniotic fluid from the uterus for testing or treatment purposes). Therefore, complications such as premature rupture of membranes, infection and premature labor are very rare.
Depending on the stage of Twin to Twin Transfusion Syndrome (TTTS), the treatment should be taken to avoid unnecessary complications.