Treatment of twin-to-twin transfusion syndrome
The natural outcome of twin-to-twin transfusion syndrome involves high in utero or neonatal morbidity and mortality rates in the majority of cases; the incidence of neurological disability is 40–80% and the rate of mortality is almost 100% in cases that develop before week 20 and 80% if the onset is between weeks 21 and 26.
Early diagnosis and timely treatment are key factors in improving the prognosis. The condition requires urgent treatment, within a few days of the diagnosis, because it can worsen very quickly.
The first-choice treatment for severe cases of twin-to-twin transfusion syndrome is a surgical intervention: foetoscopic laser surgery.
Foetal surgery (foetoscopy) is the treatment of choice in twin-to-twin transfusion syndrome. It was proposed as a treatment for TTTS at the beginning of the 1990s.
Foetoscopic laser surgery is a minimally invasive procedure. A 3 mm incision is made in the skin and then a cannula (trocar) equipped with a camera and fibre optic cable is inserted into the uterine cavity.
Twin-to-twin transfusion syndrome is a problem associated with the placenta, not the foetuses, and so the treatment is also focused on the placenta. An endoscope provides a direct view of the placenta and is used to identify the interconnecting blood vessels which are subsequently coagulated with a laser. The aim is to eliminate all the vascular connections between the two foetuses and divide the single placenta into two independent placental territories, as if it were a dichorionic pregnancy.
This intervention is usually performed under local anaesthesia with sedation so that the expectant mother is more relaxed. She will be asleep but breathing spontaneously.
Patients must adhere to total bed rest for the first 24 hours after the procedure. The first ultrasound control is taken after 24 hours and so long as there are no complications the patient can start moving around and will be discharged to their home.
Patients attend weekly ultrasound check-ups in the weeks following the intervention and are indicated relative rest and sick leave until the end of the pregnancy. Relative rest means avoiding pressure on the abdomen (do not lift heavy objects or carry out any exercises that increase abdominal pressure) and being active for short periods but frequently (moving around the house, walking for 5–10 minutes).
A second-choice treatment is that of amniodrainage. Amniodrainage consists of introducing a needle into the amniotic cavity to extract the excess fluid from the recipient’s amniotic sac and therefore reduce the pressure and the risk of a preterm birth.
The results of amniodrainage are evidently inferior to those of foetoscopic laser surgery and so it is only used in cases where the latter is either impossible or contraindicated.
The mean survival achieved through this method is close to 60% and the rates of neurological disability are higher than those observed with laser treatment. Amniodrainage manages to extend the pregnancy but it is only a symptomatic treatment and does not deal with the cause of the disease – the transfusion of blood across the aforementioned anastomoses.
The most frequent complications are:
- Premature rupture of membranes (PRM). This occurs when the amniotic sac breaks and amniotic fluid leaks out of the uterus. It occurs in 10–20% of cases of TTTS. It is a frequent complication that does not usually imply a loss of pregnancy.
- Preterm birth (PB). Foetuses that undergo laser surgery have a mean gestational age of 33 weeks at delivery. Approximately 5–8% of cases terminate in extremely preterm births (before 28 weeks).
- Pregnancy loss. This occurs in approximately 5-10% of all cases due to a preterm birth, rupture of membranes or no tolerance of the fetus to treatment. The treatment for twin-to-twin transfusion syndrome brings about an abrupt end to the volume overload in the recipient, while the donor foetus’ volume increases suddenly; both foetuses have to adjust to this new situation quickly. In some cases they are unable to adapt and subsequently die.
- Selective growth retardation. The act of dividing the placenta into two parts, thereby converting the foetuses into independent twins, means that each foetus now has its own placental territory. If the placental division is very uneven, then the foetus with too little placenta is exposed to the risk of selective growth retardation. The risk is greater whenever the preoperative growth discordance between the two foetuses is greater than 30–35%. Severe cases of selective growth retardation can lead to foetal loss.
- Neurological complications for the surviving foetus. Various values have been reported for the rate of neurological complications in twin-to-twin transfusion syndrome (2–20%). The most recent publications, which incorporate greater treatment success rates and improved foetoscopic monitoring protocols for treated foetuses, report lower incidences (2–8%) of neurological impairment prior to delivery in half of all cases. This complication generally affects recipients and is mainly associated with prematurity.
- Intra-amniotic infection. This is a relatively rare complication due to the use of prophylactic antibiotics during surgery. Nevertheless, it still occurs in up to 1% of cases and the consequences are pregnancy loss and/or premature birth.
- Reverse twin-to-twin transfusion syndrome. This occurs when the donor foetus transforms into the recipient and vice versa. Although very rare, a small percentage of cases will require another intervention to treat it.
- Onset of twin anaemia-polycythaemia sequence (TAPS). This is a recently identified form of twin-to-twin transfusion syndrome known as twin anaemia-polycythaemia sequence (TAPS) in which the twins have different haemoglobin levels and a lack of oligo-polyhydramnio sequence.
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