What is Twin-Twin Transfusion Syndrome ? (TTTS)
Twin –Twin Transfusion Syndrome (TTTS) is a serious complication of twin pregnancies where the babies share a placenta (monochorionic). TTTS occurs in 10-15% of these pregnancies. Twins that are monochorionic also share blood vessel connections on the surface of the placenta that connect their circulations.
In TTTS, an imbalance develops between the circulations of the two twins. The result of this imbalance is a (donor) baby that is “dehydrated” with only a small amount of amniotic fluid around it because it is not producing as much urine (oligohydramnios). The other baby (recipient) develops a large amount of amniotic fluid around it (polyhydramnios), because it tries to get rid of the extra fluid in its circulation by urinating. The recipient may develop heart failure from the additional blood volume and its response to it. Differences in fetal size and growth rate are more often related to the relative percentage share of the placenta each baby has than to the fact that TTTS is ongoing. If severe cases of TTTS go left untreated there is an 80-100% chance of fetal death.
Diagnosis of Twin-Twin Transfusion Syndrome
TTTS is diagnosed by ultrasound, usually between 16-22 weeks of pregnancy. TTTS has been divided into stages to assist in assessing the severity, the need for and the most appropriate treatment option for any given case. Individual pregnancies do not necessarily progress through these stages but may skip them or stop at one stage or even regress. This staging was proposed by Dr Ruben Quintero, one of the pioneers in the field.
- Stage I: Donor with oligohydramnios and small bladder visible; polyhydramnios in recipient. The deepest pocket of fluid measures >8cm in recipient sac, <2cm in donor sac before 20 weeks, >10cm in the recipient sac after 20 weeks.
- Stage II: Donor with oligohydramnios (deepest vertical pocket <2cm), bladder remains unfilled; polyhydramnios (>8cm or 10cm depending on age) in recipient.
- Stage III: Critically abnormal blood flow studies (Doppler) in the umbilical cords or blood vessels of either twin.
- Stage IV: Abnormal fluid collection (hydrops) in one of the twins, usually the recipient, from severe heart failure.
- Stage V: Death of one of the twins.
Treatment Options
There are two main treatment choices available for TTTS currently, serial amnioreduction and laser therapy.
Serial Amnioreduction
Serial amnioreduction is the removal of excess amniotic fluid from around the recipient baby. This is repeated as often as necessary, depending on how fast the fluid reaccumulates. This treatment may be used in milder cases of TTTS, but has not been shown to be as effective in severe cases, particularly if the recipient has signs of a weakening heart. Serial amnioreduction has an overall average success rate of 50-65% (at least one twin surviving). As many as 30% or more of those survivors may have some neurological handicap.
Laser Therapy
In severe cases of TTTS, the only treatment that has been shown to stop the underlying process, and allow the twins to regain their health and decrease the occurrence of neurological injury, is laser photocoagulation therapy. Laser photocoagulation uses a light (laser) to close the blood vessels that the babies share connecting their circulations on the surface of the placenta.
In general, survival rates with fetoscopic laser photocoagulation have been around 80% (at least one twin surviving) and 60-70% overall. Survivors have approximately a 5-10% chance of some neurological injury. As effective as this treatment appears to be it is not risk free for the mother, the pregnancy or the fetuses, and this has to be weighed carefully.
