2.1.1 Approximately 70% of monozygotic twins are monochorionic/diamniotic (one placenta with two amniotic sacs). TTTS affects approximately 15% of these pregnancies and perinatal mortality is up to 80% if the syndrome is left untreated. TTTS results from abnormal shunting of blood between the circulations of the unborn twins through anastomoses of the vessels of the shared placenta. Blood is transfused from the donor twin, whose growth becomes restricted and who develops oligohydramnios or anhydramnios (too little or absent amniotic fluid), to the recipient, who usually develops circulatory overload, cardiac compromise and polyhydramnios (too much amniotic fluid). The combination of polyhydramnios in the recipient and oligo/anhydramnios in the donor squashes the donor twin against the wall of the uterus. The syndrome is associated with high morbidity and mortality for both twins. Morbidity among survivors includes cardiac, renal and serious neurological impairment, such as cerebral palsy. About 15% of survivors have long-term neurological sequelae.
2.1.2 The options for managing TTTS include expectant management, amnioreduction, septostomy, laser ablation, and selective fetal termination using techniques such as umbilical cord occlusion. In some cases the treatment aim is to enable one twin to survive, as the chances for both surviving are extremely poor. Some parents may choose to terminate the pregnancy because of the high risk of perinatal morbidity and mortality in both twins and the risks of serious long-term morbidity in survivors.
2.2.1 The procedure is performed under regional analgesia or local anaesthesia with maternal sedation. Under ultrasound guidance, a cannula and needle are inserted through the maternal abdominal wall, uterine wall and into the amniotic sac of the recipient twin. The needle is removed, and a fetoscope with a thin fibre to carry the laser energy is then inserted through the cannula. The fetoscope is used to look at the blood vessels on the surface of the placenta. Placental vessels are then coagulated using the laser. After completion of surgery, excess amniotic fluid in the recipient twin's sac is removed to achieve a normal volume.
2.3.1 In a systematic review that included 10 studies (n = 981) assessing laser ablation (both non-selective and selective) for the treatment of TTTS, overall perinatal survival ranged from 61% (87/142) to 70% (210/300); rates for survival of at least one twin ranged from 61% (11/18) to 83% (79/95). In a systematic review that included a single randomised controlled trial of selective laser ablation versus amnioreduction, the likelihood of at least one twin surviving to 28 days was higher with laser ablation than with amnioreduction: 76% (55/72) versus 51% (36/70; p = 0.002). This difference was also maintained to 6 months of age (p = 0.01).
2.3.2 Postnatal neurological sequelae were reported in 8 of the 10 studies included in the systematic review. The incidence of postnatal neurological morbidity ranged from 1% (1/87) to 8% (2/26). Two additional case series that specifically evaluated long-term neurological sequelae reported major neurological abnormities in 6% (10/167) and 11% (10/89) of twins treated with laser and followed up postnatally for a median of 22 and 38 months, respectively. In the randomised controlled trial it was reported that babies in the laser ablation group were more likely to be free of neurological complications at 6 months of age than those treated with amnioreduction (52% [75/144] vs 31% [44/140]; p = 0.003). For more details, refer to the 'Sources of evidence' section.
2.3.3 The randomised controlled trial also reported that median gestational age at delivery was significantly prolonged in the laser ablation group compared with the amnioreduction group (33 weeks versus 29 weeks; p = 0.004). Similar results were reported in a non-randomised controlled trial of 173 women with reported median gestational age at delivery to be 33 weeks in the laser group compared with 29 weeks in the amnioreduction group.
2.3.4 Only one study (n = 101) reported recurrence of TTTS following the procedure in 14 (14%) of pregnancies.
2.3.5 The Specialist Advisers commented that there are some uncertainties about whether the procedure reduces the incidence or severity of long-term neurodevelopmental outcomes, and the degree of selectivity required when performing laser ablation. They also expressed uncertainty as to the best treatment for early-stage TTTS.
2.4.1 The most common maternal complication following laser surgery was premature rupture of the membranes, which occurred in 28% of women (49/175) in a case series evaluating the perioperative complications of laser ablation; 12% (6/49) occurred within 3 weeks of the procedure. In the randomised controlled trial, premature rupture of the membranes within 28 days of the procedure occurred equally in the two groups (9%). Placental abruption and pregnancy loss (miscarriage) occurred in 2% (3/175) and 7% (12/175) of women, respectively, in the case series; and in 1 out of 69 pregnancies (1%) in the laser ablation group and in 2 out of 68 (3%) in the amnioreduction group in the randomised controlled trial. In the randomised controlled trial, pregnancy loss within 7 days after the procedure occurred in 8/69 (12%) of women in the laser ablation group and 3% (2/68) in the amnioreduction group (p = 0.1). Other complications reported in the studies included amniotic fluid leakage and vaginal bleeding. For more details, refer to the 'Sources of evidence' section.
2.4.2 The Specialist Advisers listed potential complications as premature rupture of the membranes, infection (chorioamnionitis), pregnancy loss, iatrogenic intrauterine death of the donor twin and sometimes of the recipient twin, persistent TTTS and reverse transfusion. The Specialist Advisers also noted that there was a risk of maternal death, although this risk has been reduced with improvements in the technique.