Twin-Twin Transfusion Syndrome (TTTS)

Friday, May 19, 2017

Serial Amniocentesis

TTTS. Serial Amniocentesis

Amniocentesis is the standard screening technique for fetal anemia, because amniotic fluid contains hemolytic products excreted from the fetal kidneys and lungs, including bilirubin.

Amniocentesis (also referred to as amniotic fluid test or AFT) is a medical procedure used in prenatal diagnosis of chromosomal abnormalities and fetal infections, and also for sex determination, in which a small amount of amniotic fluid, which contains fetal tissues, is sampled from the amniotic sac surrounding a developing fetus, and then the fetal DNA is examined for genetic abnormalities.

The most common reason to have an "amnio" is to determine whether a baby has certain genetic disorders or a chromosomal abnormality, such as Down syndrome. Amniocentesis (or another procedure, called chorionic villus sampling (CVS)) can diagnose these problems in the womb. Amniocentesis is performed when a woman is between 14 and 16 weeks gestation.

Women who choose to have this test are primarily those at increased risk for genetic and chromosomal problems, in part because the test is invasive and carries a small risk of miscarriage. This process can be used for prenatal sex discernment and hence this procedure has legal restrictions in some countries. Amniocentesis was first introduced by American obstetrician Fritz Friedrich Fuchs and Danish gastroenterologist Polv Riis in 1956 for fetal sex determination and up to mid 1970s amniocentesis were done 'blind‘.

TTTS. Septostomy

The rationale on the use of septostomy or dividingmembrane amniorrhexis for the treatment of TTTS was to equilibrate the amniotic pressures on both sides of the membrane.10,11 Prior to its proposal, a difference in amniotic fluid pressures in the two sacs was never demonstrated.

On the contrary, Quintero and others showed that, in fact, the pressure in both sacs is similar.12,13 Notwithstanding, a randomized controlled trial was carried out to compare septostomy versus amnioreduction.14 The study was terminated at the planned interim analysis stage after 73 women were enrolled.

TTTS. Medical Treatment

Medical treatment of TTTS has included only isolated case reports involving the use of digoxin3–5 or indomethacin.6–8 The rationale for the use of digoxin is to treat a recipient twin in heart failure.

Relatively high maternal serum levels of digoxin must be achieved in order to reach therapeutic levels in TTTS, as the mean feto–maternal gradient is 0.56.9 Fetal levels are also directly related to GA.

Treatment of twin–twin transfusion syndrome: an evidence-based analysis

Management of twin–twin transfusion syndrome (TTTS) has encompassed a wide spectrum of options, including expectant management, medical therapy, and surgery, as well as pregnancy termination.

Over the past few years, significant emphasis has been given to the development of clinical practice guidelines that are derived from evidence-based medicine.

Twin to Twin Transfusion Syndrome. Results

Between July 1997 and June 2002, 252 patients with the diagnosis of TTTS underwent surgical treatment at our center. UCO was performed on 36 (14.3%) of these patients. Ten cases were excluded from the analysis because they had undergone secondary UCO after an attempted SLPCV (technical success rate for TTTS 216/226, or 95.5%).

One additional case was excluded because the ligated cord was that of a recipient twin that had died shortly before surgery. Thus, 25 cases of TTTS underwent primary UCO. Six (24%) had cord occlusion of the donor fetus (donor group) and 19 (76%) of the recipient fetus (recipient group). Six fetuses had the following discordant fetal malformations: 2 had neural tube defects (both donors), 1 had body-stalk anomaly (donor), 1 had pulmonary atresia (recipient), 1 had anencephaly (recipient), and 1 had intracranial hemorrhage (recipient).

Twin-Twin Transfusion Syndrome. Surgical technique

The two methods of cord occlusion performed were umbilical cord ligation (UCL) or umbilical cord photocoagulation (UCP). UCL was performed via a 3.5 mm trocar inserted percutaneously into the amniotic cavity via 1–2 mm skin incision under continuous ultrasound guidance and general or local anesthesia.

The cord of the target fetus was identified endoscopically with a 2.7–3.3 mm diagnostic or operating endoscope (Richard Wolf, Inc., Vernon Hills, IL, USA). A 3-0 Vicryl suture that had been previously threaded through a custom-designed knot-pusher was passed down the working channel of the endoscope with a semi-automatic grasper (Cook Ob/ Gyn, Spencer, IN, USA), or through a second port, and was laid underneath the target umbilical cord.

TTTS. Methods

Standard sonographic diagnostic criteria for TTTS included polyhydramnios in the recipient twin (maximum vertical pocket [MVP] ?8 cm), oligohydramnios in the donor twin (MVP ?2 cm), single placenta, same gender, and thin-dividing membrane with absent ? or twin-peak sign.

Each case was prospectively classified using the Quintero staging system,15 as described in Chapter 7. Primary UCO was offered if there was (1) presence of a lethal discordant fetal anomaly, or (2) stage III/IV in a patient who elected this modality.

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.

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.

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 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 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.

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 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.

TTTS. Removal of the trocar

Once the desired level of amniotic fluid volume in the sac of the recipient twin is reached, the suction–irrigation trumpet is removed and the patient is alerted to the removal of the trocar. Trocar removal is monitored with ultrasound to detect bleeding from the anterior uterine wall or membrane detachment.

If neither occurs, the incision is covered with a band-aid, steri-strips or dermabond to conclude the surgery. Bleeding from the anterior uterine wall may occur at any point during surgery, but most commonly after removal of the trocar. Bleeding is typically short-lived, and can usually be contained with external digital pressure over the incision site of approximately 5 minutes.

TTTS. Post-laser amniodrainage

Surprisingly, the topic of how much fluid should be removed during a therapeutic amniocentesis has received relatively little attention.18 Descriptive terms such as ‘aggressive’ or ‘radical’ have been used to describe the philosophical objective of the procedure.

Objectively, goals range from decreasing the amniotic fluid volume to the level of oligohydramnios or to low-normal levels, using either MVP (maximum vertical pocket) or AFI (amniotic fluid index) as the measuring parameter.19–22 Most centers advocate reducing the MVP to a level of 5–6 cm.

Lasering of AV anastomoses

AV anastomoses can be interrupted by lasering the artery, the vein, or both. In theory, lasering of the vein still allows for blood to be lost into the cotyledon, and may be responsible for development of intraoperative fetal anemia. Therefore, when possible, we prefer to laser the artery first. Most placentas will have both AVDRs and AVRDs.

Whenever possible, we prefer to laser AVDRs first followed by AVRDs, as this may allow for an intraoperative transfusion of the donor twin (sequential technique, or SQLPCV). Lasering of superficial anastomoses Lasering of AA and VV anastomoses requires that the surgeon decide where, along the path of the vessel, the interruption needs to be made (Figure 9.11a and b).

Selective laser photocoagulation of communicating vessels

There are three steps in performing selective laser photocoagulation of communicating vessels (SLPCV). The first step is a diagnostic one, which consists of the identification of all of the anastomoses, differentiating them from individually perfused areas of the placenta (diagnostic fetoscopy step).

The second step consists in the actual lasering of the anastomoses. The third step involves reviewing all of the lasered anastomoses and relasering if necessary, as well as endoscopic review of any other important aspects of the amniotic cavity or fetuses.

TTTS. Trocar entry

In standard laparoscopy, the trocar insertion sites have been extensively worked out to avoid injury to the superficial epigastric vessels. In contrast, the site of entry into the amniotic cavity of the recipient twin will vary from patient to patient.

The site of entry is chosen after careful preoperative mapping (Chapter 7) to avoid injury to the dividing membrane or the placenta. Injury to the superficial epigastric vessels is avoided by placing the trocar either at the midline or 8 cm lateral from the midline.15 Power angio Doppler insonation of the myometrium under the proposed site of entry may disclose important vessels that need to be avoided (Figure 9.9).

Patient positioning, prepping, and draping

Chapter 15 discusses in detail the operating room preparation of the patient. The patient is placed in the decubitus position. A left or right lateral tilt may be required if the patient develops hypotension from caval compression. The dorsolithotomy position is chosen in selected cases to avoid an anterior placenta and if no access from the right or the left side of the patient is available. A Foley catheter is placed in the bladder. The patient is then fully prepped and draped as for any major surgery.

Anesthesia

Chapter 18 discusses in detail our experience with general and local anesthesia. Most centers today use local anesthesia in the form of 1% lidocaine without epinephrine. A 10 ml syringe with a 21-gauge 11/2 inch needle is used. The skin is infiltrated to create a wheal. The needle is then inserted under ultrasound guidance to infiltrate the tissues to the level of the uterine serosa.

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