Supraselective laser

Supraselective laser photocoagulation of communicating vessels

SLPCV results in a functional or surgical dichorionization of a monochorionic placenta. Indeed, as a result of obliterating all vascular anastomoses, the remaining placental cotyledons are perfused individually by each twin (individual placental territory, or IPT). 

All shared cotyledons, with the exception of three-vessel or four-vessel cotyledons, are rendered non-functional. Survival of any one twin after SLPCV depends, at least partially, on whether the remaining IPT is enough to sustain in-utero life (see Chapter 5) 

There are typically 20 cotyledons in a monochorionic placenta. What determines the percent of shared vs individual cotyledons in any given monochorionic placentation is not known, but at least theoretically, one of three permutations could potentially exist: 

• Both fetuses have enough IPT to survive in utero after SLPCV. In this situation, the percent shared cotyledons is low, and each twin has an adequate IPT. 

• Only one of the fetuses has enough IPT to survive after SLPCV. In this situation, one of the fetuses has an inadequate IPT as a result of unequal placental distribution. 

• Neither twin has enough IPT to survive after SLPCV. In this situation, both fetuses are interdependent for their survival, with blood having to go through the other twin before it comes back oxygenated. We have dubbed this placental model ‘circular pattern.’ 

Typically, the amount of IPT cannot be determined sonographically or endoscopically. However, if during the diagnostic fetoscopy step of SLPCV a circular pattern becomes obvious, dual in-utero demise after SLPCV can be predicted. Thus, a variation in the SLPCV technique must be performed. 

This can be done by targeting only one or a few (not all) of the AVDRs to decrease the amount of blood being lost by the donor twin, in an empiric attempt to balance the blood exchange between the fetuses. We have named this technique ‘supraselective SLPCV, or SSLPCV.’ 

Patients treated with SSLPCV continue to have patent vascular anastomoses. Although TTTS may resolve, patients treated with this technique are at risk for developing persistent or reverse TTTS, or any of the untoward consequences of spontaneous in-utero demise of one of the twins.