Monoamniotic twins

Selective laser photocoagulation of communicating vessels in monoamniotic twins

Contrary to common belief, TTTS does occur in monoamniotic twins and is thought to occur in approximately 10% of monochorionic twins. Since monoamniotic twins represent approximately 1% of all monochorionic twins, TTTS would occur in 0.1% of monochorionic twins, or approximately 1:24 000 pregnancies. 

Monoamniotic twins may have any of the above placental distribution patterns, but, in particular, may be more prone to have extensive vascular anastomoses and a circular placental vascular pattern. In addition, the distance between the cords may be exceedingly short, with large AA or VV anastomoses. Cord entanglement may also be present, placing the fetuses at an increased risk of in-utero demise from this complication. 

Most cases, however, may simply show intertwining of the cords and not have a true knot. SLPCV can be contemplated in monoamniotic twins provided cord entanglement is not present. If a circular pattern is suspected, SSLPCV may need to be performed instead. If a short intercord distance exists and large AA and/or VV anastomoses exist, trocar assistance and inching technique with high wattage may achieve vessel obliteration while trying to avoid thermal injury to the umbilical vein. If cord entanglement is present, serial amniocentesis or umbilical cord occlusion and transection may be the only alternatives left. 

CONCLUSION 

Laser surgery for TTTS is highly technologically and technically dependent. Over the years, we have developed both the appropriate instrumentation as well as the specific surgical techniques to address the surgical task in every specific instance. Attention to all technical details is pivotal in order to complete the surgery successfully in all cases. 

With the right equipment and surgical training, however, surgery is markedly facilitated and expedited. Success with SLPCV worldwide has resulted in increasingly more centers being involved with the laser treatment of TTTS. We hope the concepts discussed in this chapter will be of use to all of those performing or training to perform SLPCV for the treatment of TTTS.