REVIEW ARTICLE

https://doi.org/10.5005/jp-journals-10009-1974
Donald School Journal of Ultrasound in Obstetrics and Gynecology
Volume 17 | Issue 2 | Year 2023

Laser Treatment of Twin-twin Transfusion Syndrome

Rubén A Quintero1, Eftichia V Kontopoulos2, Ramen H Chmait3

1–3USFetus Research Consortium, Miami, Los Angeles, United States of America

Corresponding Author: Rubén A Quintero, USFetus Research Consortium, Miami, Los Angeles, United States of America, Phone: +13056673793, e-mail: quintero@usfetus.org

Received on: 10 March 2023; Accepted on: 15 April 2023; Published on: 30 June 2023

ABSTRACT

Objective: Laser ablation of all placental vascular anastomoses is the optimal treatment for twin-twin transfusion syndrome (TTTS). This requires proper endoscopic identification of the anastomoses and adequate photocoagulation. However, two important controversies have recently become apparent—(1) a gap between concept and performance and (2) a question as to whether all the anastomoses can indeed be identified endoscopically and therefore, whether blind lasering of healthy placental tissue between anastomoses is justified. The purpose of this paper is to address the potential source of the gap between concept and performance and to discuss the optimal surgical technique.

Materials and methods: Laser surgery for TTTS can be broken down into two fundamental steps—(1) endoscopic identification of the placental vascular anastomoses and (2) laser ablation of the anastomoses. Regarding the endoscopic identification of the laser targets, the nonselective technique is based upon lasering all vessels crossing the dividing membrane, whether anastomotic or not. The selective technique identifies all anastomoses and occludes only such vessels. The Solomon technique involves lasering healthy areas of the placenta between lasered anastomoses, as it assumes that not all anastomoses are endoscopically visible. Regarding the actual laser ablation process, successful achievement of complete surgical ablation (i.e., lasering all the anastomoses) can be measured by how often the selective technique can be performed, by the rate of postoperative persistent or reverse TTTS (PRTTTS) or postoperative twin anemia-polycythemia sequence (TAPS), and by the rate of residual patent placental vascular anastomoses (RPPVAS) on surgical pathology analysis of the placenta. Articles representing the different techniques are discussed.

Results: The nonselective technique is associated with the lowest double survival rate (35%), compared with 60–75% of the Solomon or the Quintero selective techniques. The Solomon technique is associated with a 20% rate of RPPVAS, compared to 3.5–5% for the Quintero selective technique (p < 0.05). Both the Solomon and the Quintero selective techniques are associated with a 1% risk of PRTTTS. Adequate placental assessment is highest with the Quintero selective technique (99%) compared with the Solomon (80%) or the “Solomon standard” (60%) techniques (p < 0.05). A surgical performance index is proposed.

Conclusion: The gap between concept and performance responsible for suboptimal clinical results gave rise to the Solomon technique. Unfortunately, The Solomon technique actually represents a historical backward step in the performance of the surgery, given that it is based on assuming that not all of the anastomoses are visible endoscopically. Furthermore, the Solomon technique is associated with a higher rate of residual patent vascular communications than the Quintero selective technique. The Quintero selective technique is associated with the highest rate of successful ablation of placental vascular anastomoses and with the lowest rate of persistent or reverse TTTS. The reported outcomes of the Quintero selective technique do not lend support to the existence of anastomoses beyond those that can be seen endoscopically that would justify lasering healthy placental tissue.

How to cite this article: Quintero RA, Kontopoulos EV, Chmait RH. Laser Treatment of Twin-twin Transfusion Syndrome. Donald School J Ultrasound Obstet Gynecol 2023;17(2):149–157.

Source of support: Nil

Conflict of interest: None

Keywords: Laser photocoagulation, Outcome, Treatment, Twins monochorionic, Twin-to-twin transfusion syndrome

INTRODUCTION

The treatment of twin-twin transfusion syndrome (TTTS) has evolved through the years and has included expectant-medical management,1 sectio parva,2 serial amniocentesis,3-5 and the current treatment using laser photocoagulation of the placental vascular anastomoses.6-11 The rationale for the use of laser photocoagulation in TTTS stems from the fact that:

Therefore, the goal of laser surgery is to correctly identify and ablate all of the placental vascular anastomoses responsible for the syndrome. This raises two fundamental issues:

STEP IDENTIFICATION OF THE PLACENTAL VASCULAR ANASTOMOSES

Classic placental pathology studies have shown the presence of three different types of placental vascular anastomoses—arteriovenous (AV) (so-called “deep anastomoses”), arterio-arterial (A-A), and venovenous (VV) anastomoses (A-A and VV also called “superficial” anastomoses).12 All of the anastomoses can be seen on the surface of the placenta, even if the actual anastomotic exchange occurs deep within the substance of the placenta. While some authors have suggested that there are anastomoses deep within the placental parenchyma that cannot be seen on the surface of the placenta,13 such arguments have proven untenable. While in principle, all the placental vascular anastomoses are visible on the surface of the placenta, technical issues may prevent their actual endoscopic identification, such as fetal position, angle of view or location relative to the trocar entry site.

How can all the anastomoses be identified? In the early days of laser surgery for TTTS, this was an issue of contention. The original reports suggested that the anastomoses could be identified based on their appearance, that is, based on specific patterns and angles, with drawings intended to aid in this process (identification based on pattern recognition).14 Soon it became clear that a gestalt approach to the identification of the placental vascular anastomoses was both inaccurate and impractical, given the myriad of vascular patterns that the anastomoses can actually have. Furthermore, nonanastomotic vessels (NSC) could be mistaken for an anastomosis using this approach. The lack of a practical and accurate way to identify placental vascular anastomoses was one of the most important hindrances in establishing laser surgery as a valid approach for the treatment of TTTS. This limitation led to the development by other groups of what we called “the nonselective technique.”

The Nonselective Technique

The nonselective technique was based on lasering all of the vessels that would cross the dividing membrane. By definition, this technique did not attempt to differentiate anastomotic from NSC, but rather to catch as many anastomoses as possible based on three unverifiable assumptions:

  • The dividing membrane should lie parallel to the vascular equator.

  • All vessels crossing the dividing membrane are vascular anastomoses.

  • The vascular anastomoses (vascular equator) are all within the sac of the recipient twin (where the endoscope is inserted).

The use of the dividing membrane as a proxy for the definition of anastomotic vessels was fraught with several problems. First, the location of the dividing membrane may or may not be parallel to the so-called vascular equator, the area of the placenta where the anastomoses are actually located. Indeed, the location of the dividing membrane relative to the fetal placental surface may be:

  • At an angle to the vascular equator (such that some of the anastomoses may be in the sac of the donor twin and some in the sac of the recipient twin).

  • Completely within the sac of the recipient twin, such that the vascular equator lies within the sac of the donor twin.

Second, and as a corollary, not all of the vessels crossing the dividing membrane are anastomotic vessels. Therefore, by lasers all of the vessels that would cross the dividing membrane, the risk of ablating normal vessels (i.e., nonanastomotic) could be high. Third, in the rare cases where all of the anastomoses are within the sac of the donor twin, lasering of all the vessels crossing the dividing membrane from within the sac of the recipient twin would aim only at the recipient’s vessels (with or without anastomoses), with a high-risk of demise for this fetus. The increased risk for harm to either twin from the use of a nonselective technique can be appreciated in the report by Ville et al. in 1995, where the use of the nonselective technique was associated with a dual fetal survival of only 35% and a rate of the single intrauterine fetal demise of 35% as well.9 Subsequent clinical studies showed that the use of a nonselective technique, which unnecessarily targeted NSC, was associated with an increased risk for the demise of one or both twins.9 Clearly, using the dividing membrane as a surrogate for the identification of the placental vascular anastomoses was suboptimal, albeit an improvement over nondescriptive previous reports. Thus, a better way of identifying the actual anastomoses was needed.

The Selective Technique

In 1998, Quintero et al. described the selective laser photocoagulation of communicating vessels technique (SLPCV).10 This was the first description of a precise anatomical way of identifying the placental vascular anastomoses endoscopically and differentiating them from NSC. The technique required a systematic assessment of the vascular equator from one end of the placenta to the other. Basically, this meant following each vessel on the surface of the placenta to its terminal end. If the terminal end of the artery of one twin had a returning vein to the same fetus, this was labeled as a nonanastomotic pair. On the contrary, if the terminal end of an artery was followed by a vein returning to the other twin, this was identified labeled as AV anastomosis. A-A anastomoses were apparent since the artery of one twin would continue as an artery to the other twin as well. Similarly, VV anastomoses could be identified by following an uninterrupted vein from one twin to the other. The identification of the anastomoses using the SLPCV technique did not rely on the location of the dividing membrane relative to the vascular equator. This avoided missing anastomoses located in the sac of the donor twin, regardless of whether this involved a few or even all of the placental vascular anastomoses. Identification of the anastomoses within the sac of the donor by looking through the dividing membrane was also shown to be possible. This was in contrast to previous reports which had stated that anastomoses within the sac of the donor would not be visible due to the presence of two layers of amnion.14 In fact, the two layers of amnion do not preclude visualization of anastomoses located within the sac of the donor twin, particularly if severe oligohydramnios or anhydramnios is present in the sac of that fetus. The selective technique provided a reproducible way of identifying all of the vascular anastomoses, independent of their location, a first step in the proper performance of the laser surgical technique. Quintero et al. also commented on how to document the identified vascular anastomoses. This included mentioning the type (AV, A-A, VV), size (e.g., “hair,” small, medium, large, extra-large), as well as their direction (AVDR—an AV anastomosis from donor to recipient, or AVRD—an AV anastomosis from the recipient to the donor).15 The direction of flow in A-A or VV anastomoses could be determined in some cases, provided there were significant color differences in these vessels resulting from differences in fetal oxygen saturation.16 This led to the concept of the “hemodynamic equator” or HE, which represents the collision front between the two fetal circulations within an A-A or a VV anastomosis.17 The HE allowed for the first time a better understanding of the actual behavior of A-A or VV anastomoses, which until then were thought to be bidirectional in all cases. Indeed, if the HE moves back and forth between draining vessels of either twin, the behavior of the A-A or VV anastomosis is truly bidirectional. On the contrary, if the HE only reaches a draining vessel of one twin, the function of such superficial vessel is essentially no different than an AV anastomosis (and as such, labeled as fAVDR if from donor to recipient, or fAVRD if from the recipient to the donor). Lastly, if the HE does not reach any draining vessel, the net exchange of blood between the fetuses through that vessel is zero.

The selective technique also assumed that once the vascular equator was entirely mapped, the anastomoses could all be photocoagulation (a two-step process).

The acronym used for the selective technique, that is, SLPCV, defined the systematic approach that needs to take place to identify and photocoagulate all of the vascular anastomoses. Other acronyms used to describe the performance of the laser surgery may or may not be similar to the Quintero SLPCV technique. For example, while performing SLPCV, the dividing membrane is always respected. Purposeful injury to the dividing membrane, or so-called “septostomy,” is not part of the SLPCV technique.18 Though not implicit, the performance of a laparotomy to access the amniotic cavity is also not part of the SLPCV technique. While general anesthesia was originally used in our cases,19 surgery can be best performed under local anesthesia.20 Therefore, the acronym SLPCV, should apply only to those surgeries in which access to the amniotic cavity is performed under local anesthesia, percutaneously, and following a systematic and thorough identification and obliteration only of placental vascular anastomoses.10,21,22

Lasering Healthy Interanastomotic Placental Tissue: The “Solomon” Technique

As centers began to adopt the selective technique, it became apparent that the rate of RPPVAS after laser surgery (as shown in surgical pathology of the placenta) varied significantly between centers (Table 1). Similarly, the incidence of failed surgery, defined as persistent or reverse TTTS, which is the clinical manifestation of RPPVAS after laser surgery, also varied significantly (Table 2). In a study by Robyr et al., the rate of failed surgery was 22%.23 Anemia of a surviving twin after the demise of the co-twin, which is reflective of incomplete occlusion of all placental vascular anastomoses, was also noted as a common complication. Lopriore et al. reported an incidence of 33% of RPPVAS in 52 TTTS patients treated with laser at their institution.24 In comparison, the rate of RPPVAS after SLPCV by our groups, using a common technique and common technology, has consistently been less than 5%, with no anemia after the demise of the co-twin, and an incidence of reverse or persistent TTTS of only 1–1.5% (USFetus Consortium) (Tables 1 and 2).25

Table 1: : Reported incidence of RPPVAS after laser surgery on surgical pathology analysis of the placentas. Comparisons were made relative to the lowest reported rate (P1) or between the “standard” and the Solomon techniques (P2)
Author RPPVAS P1 P2
Quintero (SLPCV), 2010 5/143 (3.5%) –
Chmait (SLPCV), 2010 5/100 (5%) 0.74
Lopriore (“Fetoscopic laser surgery”), 2007 17/52 (33%) <0.001
Slaghekke, 2014
“Standard” 26/77 (34%) <0.001 >0.05
Solomon 14/74 (19%) <0.001
Table 2: Reported incidence of clinical outcomes after laser therapy reflecting RPPVAS. Comparisons were made relative to the lowest reported rate
Author Reverse or persistent TTTS p
Chmait et al.37 1/100 (1%) –
Kontopoulos et al.36 5/417 (1.5%) 1.0
Robyr et al.23 14/101 (13.8%) 0.0006
Lopriore et al.24 2/52 (3.8%) 0.27
Slaghekke et al.29
 “Standard” 9/135 (6.7%) 0.046
 Solomon 2/137 (1.5%) 1.0
Baschat et al.28
 “Selective” 6/71 (8.5%) 0.02
 Solomon 3/76 (3.9%) 0.31
Ruano et al.27
 “Selective” 4/76 (5.3%) 0.17
 Solomon 0/26 (0%) 1

In view of the relatively high incidence of RPPVAS seen by some groups, some authors proposed “connecting the dots” between photocoagulation areas on the surface of the placenta.26 The premise behind this idea was that by lasering areas between laser-ablated placental vascular anastomoses, such “blind lasering” would capture “anastomoses” that would have been presumably missed (“not visible”).13 The argument was based on the assumption by such authors that not all of the placental vascular anastomoses can be identified endoscopically,13 and that therefore, ablating only the visible ones using the selective technique, could miss vascular anastomoses. This would explain their high rate of RPPVAS. The resulting surgical technique of lasering healthy interanastomotic areas of the placenta was dubbed “the Solomon technique,”26 in reference to the biblical passage where, in order to resolve a dispute between two alleging mothers of a child, King Solomon proposed to cut the baby in half (1 Kings 3:16–28, New International Version). The analogy, therefore, is that by lasering the areas of the placenta between endoscopically-identified and laser-ablated vascular anastomoses, the placenta would be “cut in half.” Recent studies suggest that indeed, relative to the surgical groups’ prior experience with the selective technique, the use of the Solomon technique was associated with improved perinatal outcomes.27,28

Which Laser Technique is Better?

To test whether the Solomon technique could indeed reduce the rate of RPPVAS, an open-label randomized clinical trial was conducted in Europe (the Solomon trial) comparing the Solomon technique with the “standard” technique.29 The latter, although not specifically defined, was intended to refer to the Quintero selective technique (SLPCV). Interestingly, the study showed that the actual rate of persistent RPPVAS was no difference between the two Solomon techniques or the “standard” technique (14/74, 19% vs 23/77, 29.8%, Solomon vs “standard,” respectively, p = 0.12). However, the study did show a decreased rate of persistent or reverse TTTS (2/137, 1% vs 9/135, 7%, Solomon vs “standard,” respectively, p = 0.03) and of TAPS (4/137, 2.9% vs 21/135, 15.5%, Solomon vs “standard,” respectively, p ≤ 0.001). Although the rationale and primary outcome of the study (to reduce the rate of RPPVAS) was no difference between the groups, the authors concluded that the Solomon technique was superior to the “standard” technique. Two additional observational studies comparing the Solomon technique with the selective technique also appeared to show favorable results relative to cohorts treated with the selective technique.27,28

Table 1 shows the rate of RPPVAS reported by the different groups using either the Quintero selective (SLPCV) technique, or the “standard” or the Solomon technique reported in the Solomon trial. As can be seen, the rate of RPPVAS is lowest using the Quintero SLPCV compared with the “standard” or Solomon techniques. Table 2 shows that the Quintero SLPCV technique is also associated with a lower rate of persistent or reverse TTTS than that of the “standard” technique reported in the Solomon trial and the “selective technique” of other authors and that the Solomon technique in all studies achieves the same rate of persistent or reverse TTTS than that reported with Quintero SLPCV. Given that the Solomon technique is still associated with approximately 20% of RPPVAS, the initial rationale for the technique, that is, to reduce the high rate of RPPVAS, does not appear to hold. Furthermore, given that the proponents of the Solomon technique have also shown that most missed anastomoses are located in the margins of the placenta,24 lasering inexistent placental vascular anastomoses in otherwise healthy placental tissue between vascular anastomoses within the main body of the placenta is incongruent with the rationale (Table 3 and Fig. 1). Altogether, the Solomon technique would seem to represent a backward step in the ability to correctly identify all of the placental vascular anastomoses, by accepting the unproven theory of the presence of nonvisible placental vascular anastomoses on otherwise healthy-appearing fetal surface of the placenta. Alternatively, we have shown that all of the placental vascular anastomoses can be clearly identified without having to ablate inexistent anastomoses in healthy placental areas. Stated differently, the use of the “Solomon technique” may simply represent an attempt to achieve similar results as those which can be obtained with the performance of the Quintero SLPCV technique, rather than a true advantage over the SLPCV technique, at the expense of lasering healthy placental tissue.

Table 3: Principles and results of the use of the Solomon technique to identify and ablate all placental vascular anastomoses in TTTS
Purpose of the surgery Purported location of the RPPVAS Actual location of the additional laser ablations Rate of RPPVAS29 Rate of RPPVAS (USFetus group)30,37
To decrease the rate of RPPVAS after laser therapy Mostly on the margins of the placenta Within the body of the placenta, between endoscopically identified vascular anastomoses 30% (“Standard” vs 19% Solomon) p > 0.05 5% p < 0.05 relative to Solomon technique

Figs 1A and B: (A) Selective photocoagulation of communicating vessels (SLPCV). All of the anastomoses are photocoagulated, regardless of their location relative to the dividing membrane, while sparing nonanastomotic vessels. Rate of RPPVAS: 3.5–5%36,37; (B) Solomon modification of the SLPCV technique. The fetal surface of the placenta between endoscopically identified anastomoses is also lasered, to occlude “anastomoses” not visible by the endoscope. Note that marginal anastomoses may be missed, as they are not between laser shots. Rate of residual patent vascular anastomoses: 20%.29

ABLATION OF THE PLACENTAL VASCULAR ANASTOMOSES

Assuming that there is a conceptual agreement on how to identify the anastomoses, the next step consists of being able to ablate them. Successful ablation of the placental vascular anastomoses assumes that the surgeon can adapt to the different clinical scenarios and overcome the various challenges that may be present in each case. Particular known surgical challenges include:

The management of each of these challenges requires the use of special techniques or technology, including the use of fluid management systems, blunt probes, trocar assistance,30 and special laser photocoagulation techniques, which are beyond the scope of this article.31 A recent Delphi study outlined the multitude of steps needed to perform the surgery. Most authors agreed on the basic surgical goal (the purpose of the Delphi survey), including the ablation of all of the placental vascular anastomoses along the vascular equator, without injuring healthy placenta or NSC.32 The question is—how often can these goals be accomplished while overcoming the various challenges mentioned above? One way to address this question is by noting how often can the placenta be adequately assessed and how often can the vessels be selectively ablated.

Adequate Placental Assessment

Adequate placental assessment refers to the ability of the surgeon to survey the entire vascular equator. For example, in a sub-analysis of the Solomon trial, the authors reported that they were able to adequately assess the placenta in only 65 out of 74 patients in the Solomon group (87%) and in only 69 out of 77 (89%) in the “standard” group.33 The reasons behind the inability of the surgeons to adequately assess the placenta in >10% of the cases in each group were not stated. Obviously, if the placenta cannot be adequately assessed, this is likely to result in missed anastomoses and thus an increased likelihood for adverse clinical outcomes, including persistent or reverse TTTS. In contrast, our group has shown consistently the ability to assess the placenta adequately in over 99% of the patients.34

Selective Ablation of the Anastomoses

Another surgical competency benchmark refers to the ability of the surgeon to selectively ablate the vascular anastomoses without including NSC. To address this issue, a “selectivity index” (SI) was proposed by Stirnemann et al., as , where SC are the selectively coagulated vessels and NSC are the nonanastomotic vessels. NSC were also vessels that were considered presumed anastomoses, but that could not be followed to their terminal end and were nonetheless lasered. In their experience, most surgeries involved lasering both anastomotic and nonanastomotic vessels.26,35 A “high” SI defined as—0.25 was reported by the authors to correlate with improved postnatal survival at 28 days of at least one twin and both twins. Crisan et al. showed that the SI proposed by Stirnemann et al. is mathematically inaccurate and should not be used to assess the adequacy of laser surgery.34 Instead, a simpler index consisting of a ratio between how often the surgery can be done using the Quintero selective technique vs nonselectively, is more representative and easier to understand: , where QSI is the Quintero selectivity index, SLPCV is a surgery performed selectively, NSLPCV is a surgery where at least one vessel was not clearly identified as an anastomosis but was lasered. For example, in the article by Stirnemann, the authors showed that they were able to perform selective surgery in only 34% of cases.35 In another report of 123 patients, surgery could not be completed in five cases for a stuck twin obscuring the equator (2), poor visualization (2), and a large anastomotic vessel (1).24 Obviously, the goal is to try to perform the surgery selectively as close to 100% of the time as possible.22,34,36

Accuracy of Laser Therapy

Theoretically, one could combine the rate of adequate placental assessment and selective laser surgery with the rate of either RPPVAS (when available) and the rate of persistent or reverse TTTS to determine how accurately the laser surgery is being performed at a given center or by a given surgeon. The accuracy of SLPCV could thus be defined as:

AccSLPCV = QSI*(1-RPPVA)*(1-PRTTTS)

where, AccSLPCV is the accuracy in performing SLPCV, QSI is the rate of Quintero selectively performed surgeries, RPPVA is the rate of RPPVAS (when available), and PRTTTS is the rate of persistent or reverse TTTS. Table 4 shows such a theoretical calculation and its use to compare different reports.

Table 4: Accuracy of laser surgery for TTTS
Author Rate of selectively performed surgeries First-rate of RPPVAS First-rate of persistent/reverse TTTS Accuracy of SLPCV
USFetus group34,36 98.7% 0.95 0.99 92%
Solomon29 87% 0.81 0.99 69.7%
Solomon29 “standard” 89% 0.66 0.93 54%

Should the Rate of TAPS be Included as a Benchmark for the Performance of Laser Therapy in TTTS?

The rate of TAPS has been included as a measure of failed laser therapy for TTTS, in addition to the rate of RPPVAS and persistent/reverse TTTS.27-29,33,37 The decision stems from the purported etiology of TAPS, which presumably results from the transfer of blood between two monochorionic twins through small placental vascular anastomoses in such a way that one fetus develops anemia and the other twin develops polycythemia, but without the net blood volume inequalities typical of TTTS.38 Presumably, the syndrome occurs through small caliber AV anastomoses, in contrast to larger size vessels typically seen in TTTS. The plausibility of the proposed pathophysiology of TAPS is suspect, for the following reasons:

The original theory was based on the presence of RPPVAS. Given the high incidence of RPPVAS reported from such groups (20–33%), it is not possible to discern what role, if any, these anastomoses play in the etiology of TAPS.

While TAPS has been described in the presence of RPPVAS, they are not indispensable. We and others have recently reported on the presence of TAPS without apparent placental vascular anastomoses.36,39

Contrary to TTTS, ablation of residual patent placental anastomoses in cases of TAPS may not necessarily eliminate the condition in all cases. Table 5 compares TTTS with TAPS relative to the role of placental vascular anastomoses.

Table 5: Role of placental vascular anastomoses in the etiology of TTTS and TAPS
TTTS TAPS
Can exist in the presence of placental vascular anastomoses Yes Yes
Can exist in the absence of placental vascular anastomoses No Yes36,39
Is eliminated by ablating the placental vascular anastomoses Yes Yes45

Therefore, the assumption that TAPS is only the result of unsuccessful laser therapy may not be entirely accurate. Thus, in our opinion, the inclusion of TAPS as a benchmark of failed laser therapy should be used with caution.

Functional Ablation of the Placental Vascular Anastomoses: The Sequential Technique

The development of the selective technique represented an important historical step in the surgical treatment of TTTS. SLPCV is indeed an anatomical surgical technique, which involves the identification and selective laser obliteration of the placental vascular anastomoses while preserving nonanastomotic vessels and healthy placental tissue. However, despite precise identification and ablation of placental vascular anastomoses, the intrauterine fetal demise of one of the fetuses after SLPCV would still occur in approximately 9–29% of cases with this technique.10,40 A potential explanation for this complication could be the sequence in which the anastomoses are obliterated during surgery. Indeed, since TTTS occurs from an excessive transfer of blood from the donor twin to the recipient twin, ablation of the AVDRs first would stop immediately the transfer of blood from this twin to the recipient twin. Furthermore, during the interval between the beginning and the end of the lasering of all the AVDRs, the donor twin would receive a transfusion from the recipient twin through the still-patent AVRDs until such vessels are also occluded. As a result, the donor twin, which is presumed to be hypotensive, would stop losing blood as soon as the laser process starts, while at the same time receiving an intraoperative transfusion from the recipient twin. The photocoagulation of the AVDRs first followed by AVRDs second was called the “sequential technique” or SQLPCV. Using sequential techniques, our group showed a reduction in the rate of intrauterine fetal demise of the donor twin from 21 to 7% and an increase in the double survival rate from 56 to 75%.41 Our group is currently assessing the merits of performing SQLPCV in a randomized clinical trial of the USFetus group.42 While a sequential technique may not necessarily be required in all cases, it could have an indication in patients where the condition of the donor twin would be most compromised.

The move toward a consensus that occurs in a Delphi study reflects a normative rather than informational influence (Murphy et al. 1998). In a similar vein Goodman (1987) comments that panelists may be persuaded to conform rather than express true agreement; a process that appears to mirror some of the disadvantages of informal methods of reaching consensus already stated. Delphi may best be viewed as a useful communication tool to generate debate, rather than reach a conclusion (McKenna 1994). As one supporter of Delphi has indicated, the output is at best an opinion and should be interpreted as such (Pill 1971).

Is There a Role for Umbilical Cord Occlusion in TTTS?

Interruption of the blood exchange between the fetuses can also be accomplished by occluding one of the two umbilical cords. This procedure should be contemplated only as a last resort to treat the syndrome. Unfortunately, the availability of bipolar photocoagulation and radiofrequency ablation has resulted in an unwarranted high number of selective feticide in many centers on patients that otherwise could have perhaps been treated best with laser surgery.26,43 Umbilical cord occlusion should not be offered as an alternative to laser because of limitations of the surgeon or the center unless the patient cannot be referred to another center capable of offering laser. Umbilical cord occlusion should be offered to patients with TTTS in which additional complicating circumstances may exist. This may be the case of patients with a severe congenital anomaly of one of the twins, or a moribund hydropic fetus. Since such cases are rare, the performance of selective feticide via umbilical cord occlusion in TTTS should be an exception, rather than the rule. Indeed, the counseling of our patients involves mentioning a survival rate of approximately 90 with a 5% risk of neurological damage if laser therapy is chosen, compared to 90% survival and a 5% risk of neurological damage to the surviving co-twin if umbilical cord occlusion is chosen. Therefore, since both survival and morbidity statistics are similar between the two procedures, but with umbilical cord occlusion one of the fetuses is denied the chance to survive, the justification is not there to offer feticide to an otherwise anatomically normal fetus.

CONCLUSION

It’s been >20 years since laser therapy was first proposed for the treatment of TTTS. Significant strides have been made both in establishing the scientific merit of using a laser to ablate the placental vascular anastomoses to treat the condition as well as in the various steps, techniques, and other technical aspects that allow such therapy.44 Selectively interrupting the placental vascular anastomoses without injuring healthy portions of the placenta using the Quintero selective technique, while obvious as a concept and as a surgical goal, has been associated with markedly different outcome results between centers. The Solomon technique has been proposed as a way to mitigate such differences but has not been shown to lower the high rate of RPPVAS that prompted its development. A properly performed Quintero SLPCV technique is associated with the highest rate of clinical success and with the lowest rate of failed therapy either by surgical pathology or clinical criteria. Further improvements in clinical outcomes with the use of the sequential technique, particularly for specific situations in which the donor may be at a unique disadvantage, could be expected and are being addressed in the ongoing randomized clinical trial conducted by our groups comparing SLPCV with SQLPCV. Selective feticide via umbilical cord occlusion should be the exception rather than the rule for severe cases of TTTS, and should not be performed to compensate for physician or surgical center limitations. Improvements in surgical equipment and other ancillary technology, while difficult to pursue, should continue to remain among the objectives of caregivers in this field. The education of next-generation surgeons using the wealth of information thus far gathered by the different centers should also be the main focus of all programs.

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