It is important to exclude a chromosomal abnormality before offering a fetoscopic procedure in TRAP sequence, because the incidence of chromosomal abnormality in the pump twin may be as high as 9%. Fifty-one percent of TRAP sequence pregnancies are complicated by polyhydramnios, and 75% are complicated by preterm labor.
The difference in estimated fetal weight between the pump twin and the acardiac / acephalic twin is predictive of outcome. When the acardius-to-pump twin weight ratio exceeds 0.5, adverse pregnancy outcome is predicted in 64% of cases. If this weight ratio is greater than 0.7, the adverse pregnancy outcome for the pump twin is approximately 90%.
Techniques of sectio parva (selective removal of an anomalous twin) and ultrasound-guided embolization were used in an attempt to interrupt the vascular communication between the pump twin and the acardius. These procedures have been associated with substantial morbidity and unreliable outcomes, which led to the development of fetoscopic approaches to this problem.
McCurdy and associates were the first to report a case of fetoscopic cord ligation in TRAP sequence. The acardiac / acephalic twin's cord was successfully ligated, but only after the pump twin's cord was ligated and then released after the error was recognized. The pump twin developed persistent bradycardia and was noted to be dead on ultrasound examination on postoperative day one.
Quintero et al, reported the first successful umbilical cord ligation for TRAP sequence. The fetal surgery was performed at 19 weeks of gestation, using two percutaneous trocars and a 1.9-mm endoscope. The cord was successfully ligated, and except for some mild postoperative uterine irritability, the patient responded well.
Three weeks following the procedure the mother presented with leakage of amniotic fluid that subsequently resolved. The pregnancy continued until 36 weeks of gestation, when a healthy boy was delivered.