Umbilical cord occlusion

Umbilical cord occlusion in twin–twin transfusion syndrome

As discussed in Chapter 9, the surgical treatment of twin–twin transfusion syndrome (TTTS) involves primarily laser obliteration of the anastomoses responsible for the syndrome. Occasionally, however, selective feticide of one of the fetuses must be contemplated. 

Indications for selective feticide in TTTS include a discordant anomalous twin or failed attempted laser therapy. The former are classified as being primary, the latter as being secondary selective feticides. Occasionally, patients may choose primary selective feticide after counseling, in accordance with their own personal opinions regarding potential outcomes. 

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. 

Triplet gestations

Selective laser photocoagulation of communicating vessels in triplet gestations

Triplet or higher-order multiple gestations may also develop TTTS, provided that a monochorionic placentation exists. In the case of triplets, pregnancies may be either dichorionic or monochorionic. SLPCV in dichorionic triplets differs little from that of twins, other than the unaffected ‘singleton’ may interfere with trocar access to the amniotic cavity of the recipient twin. 

In monochorionic triplets, one of three combinations may exist: one recipient–two donors, one donor–two recipients, and one donor–one recipient–one unaffected. Because vascular anastomoses will typically be present between all three fetuses, a seemingly unaffected triplet may serve as a go-between fetus between the other two. 

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) 

Selective laser photocoagulation

Selective laser photocoagulation of communicating vessels in patients with an anterior placenta

An anterior placenta presents additional technical challenges in patients undergoing percutaneous SLPCV for severe TTTS. The challenges consist of finding a placenta-free area in the anterior uterine wall through which the trocar can be inserted and being able to assess all vascular communications from that entry site. Finding a placenta-free area in the anterior wall may be difficult, particularly if the placenta is widely extended. 

In addition, anterior placentas may also ‘wrap around’ the lateral walls, precluding free access to the amniotic cavity. Approaches to the treatment of patients with anterior placentas that cannot be addressed with a straight operating endoscope have included performing a wide laparotomy with forward flipping of the uterus and entry into the amniotic cavity from the posterior wall (De Lia, pers comm); performing a mini-laparotomy and inserting a bent cannula;23 use of flexible-steerable operating endoscopes. In 2001 we published on two techniques to address patients with anterior placentas. 

Trocar assistance

TTTS. Trocar assistance

The relationship between the trocar and the endoscope varies from manufacturer to manufacturer. Most of the endoscopes available for operative fetoscopy follow the hysteroscopy design, in which the tip of the endoscope is flushed with the tip of the trocar and the back end of the endoscope locks with the trocar sheath. 

In our design, the trocar and endoscope are independent of each other, with the endoscope being purposely 4 cm longer than the trocar length. Fluid leakage is prevented not by a locking mechanism, but rather, by a rubber cap and a check-flow valve within the trocar. With our specific trocar and endoscopic design, we have developed the concept of trocar assistance. 

Anastomoses

Anastomoses within the sac of the donor twin

Vascular communications may be found within the sac of the donor twin in approximately one-thrid of patients with TTTS. 

In these patients, the anastomoses may take one of several forms: 

• Terminal end visible. In these patients, the terminal end of the vessels and, thus, the actual site of the anastomosis, can be seen. Branching prior to the anastomosis may or may not exist, but does not interfere with access to the terminal end. 

• Terminal end not visible. In these patients, the terminal end of the vessel is not visible, whether because of extensive branching of the recipient vasculature within the sac of the donor, or because of donor interference.