The perinatal mortality rate for cases of SCT diagnosed prenatally approximates 40 percent (Hedrick, 2004; Shue, 20l3). Poor prognostic factors include a solid component comprising more than 50 percent of the tumor mass and a tumor volume-to-fetal weight ratio (tumor volume divided by estimated fetal weight) exceeding 12 percent prior to 24 weeks' gestation (Akinkuotu, 2015). Fetal loss rates approach 100 percent if hydrops or placentomegaly develop (Vrecenak, 20l3). The group at the Children's Hospital of Philadelphia recommends consideration of open fetal surgery for SCT only in cases in which the tumor is completely external (Type I) and in which high cardiac output with early hydrops has developed in the second trimester (Vrecenak, 2013). For excision, hysterotomy is performed, and the external component is resected. he coccyx and any deep tumor are left in place for postnatal removal. Because tumor debulking interrupts the pathological vascular steal, normal fetal physiology may be restored.
As with open fetal surgeries, these procedures are performed at highly specialized centers, and some are considered investigational. To accomplish them, iberoptic endoscopes only 1 to 2 mm in diameter are used to penetrate the maternal abdominal wall, the uterine wall, and membranes. Instruments such as lasers fit through 3-to 5-mm cannulas that surround the endoscope. vIorbidities are generally lower than with open fetal surgery, but they still may be formidable, particularly if maternal laparotomy is required for access (Golombeck, 2006). Examples of some conditions treated by fetoscopy are listed in Table 16-2.
Indications and Technique. As discussed in Chapter 45 (p. 879), fetoscopic laser ablation of placental anastomoses is the preferred management for severe twin-twin transfusion syndrome (TTTS). It is generally performed between 16 and
FIGURE 16-4 Selective laser photocoagulation for twin-twin transfusion syndrome. The fetoscope is inserted into the recipienttwin sac and positioned over the vascular equator, which lies in between the two placental cord insertion sites. Arteriovenous anastomoses along the placental surface are individually photocoagulated using the laser. (Reproduced with permission from Shamshirsaz AA, Ramin, SM, Belfort MA: Fetal therapy. In Yeomans ER, Hoffman BL, Gilstrap LC III, et al: Cunningham and Gilstrap's Operative Obstetrics, 3rd ed. New York, McGraw-Hili Education, 201o7.) 26 weeks' gestation for monochorionic-diamnionic twin pregnancies with stage II to stage IV TTTS. These categories of the Quintero Staging System are described in Chapter 45 (p. 879) (Quintero, 1999; Society for Maternal-Fetal Medicine, 2013).
For the procedure, a fetoscope is used to view the vascular equator that separates the placental cotyledons supplying each twin (Fig. 16-4). Arteriovenous anastomoses along the placental surface of the vascular equator are photocoagulated using a 600-�m diameter diode laser or a 400-�m neodymium:yttriumaluminum-garnet (Nd:YAG) laser (Fig. 16-5). he procedure is typically performed under epidural or local analgesia. At the end, amnioreduction is performed to decrease the single deepest pocket of amnionic luid to below 5 cm, and antibiotics are injected into the amnionic cavity.