**9.1. Twin-Twin Transfusion Syndrome (TTTS)**

Chronic twin-to-twin transfusion syndrome is a specific complication of monochorionic pregnancies, almost exclusively to monochorionic diamniotic placentation. It results from an unbalanced unidirectional blood flow through placental arteriovenous anastomoses, and the proportion is up to 15% of all monochorionic pregnancies [73]. Additional factors such as vasoactive hormones are also believed to influence the development of TTTS [74].

Commonly diagnosed during routine second-trimester ultrasound scanning, its predicted peak in incidence is around 20-21 weeks of gestation [75]. The presentation is highly variable and the recipient twin may present circulatory overload and polycythemia, possibly leading to congestive heart failure and hydrops. Contrarily, the donor twin shows oliguria and oligohydramnios, as well as anemia and growth restriction. Acute unbalancement can also occur at any time before birth, threatening the prognosis [76].

Data shows that 17% of the overall twin's perinatal mortality and 50% of all perinatal deaths in monochorionic diamniotic twins are attributed for TTTS [77].

#### **9.2. Diagnostic criteria**

TTTS is properly diagnosed after confirmation of monochorionic twin pregnancy in early sonography demonstrating T-sign. In late diagnosed cases, chorionicity is supposed when single placental mass and a thin intertwin membrane are seen [78]. Besides the confirmation of a monochorionic diamniotic gestation, the presence of oligohydramnios (maximal vertical pocket <2 cm) within the donor sac, instead of polyhydramnios (maximal vertical pocket >8 cm) in the recipient sac are also essential [74, 77]. Differential diagnoses include selective intrauterine growth restriction and other causes of amniotic fluid abnormalities [77].

Additional sonographic findings usually coexist with TTTS such as significant growth discordance, absent or reversed a-wave in the ductus venous and velamentous cord insertion [74]. TTTS frequently occurs acutely and a meticulous follow-up in a specialized center is strongly recommended. The initial ultrasound assessment should include detailed anatomy scan and Doppler study, along with cervical length measurement. Fetal echocardiography is a valuable option for cardiac function evaluation [75].

#### **9.3. Severity staging**

In cases of sudden TTTS aggravation, acute polyhydramnios develops between 16 and 24 weeks. Mortality rates are high, reaching 80 to 100% in untreated disorders. There is also high occurrence of miscarriage, premature rupture of membranes, preterm delivery and sponta‐ neous death of one or both siblings [79].

Quintero's et al. [80] major classification considers cumulative evolving stages (Table 2). Initial stages only differ in the amount of amniotic fluid in both cavities, followed by signs of anuria in the donor twin (anidramnios or absence of bladder content). An abnormality in the dop‐ plervelocimetry of the donor twin precedes anasarca in the recipient twin. Final stages come with death of one or both fetuses.


**Table 2.** Quintero's staging of twin-twin transfusion syndrome

This system has some prognostic significance, but the stages not always correlate perfectly with perinatal outcomes. Over 75% of stage I TTTS cases remain stable or regress with conservative management. If treated with suboptimal approaches in non-specialized centers, the consequences can be fatal [75, 77].

#### **9.4. Management**

Other antenatal complications, including those specific to monochorionic twins, were exhaus‐

Chronic twin-to-twin transfusion syndrome is a specific complication of monochorionic pregnancies, almost exclusively to monochorionic diamniotic placentation. It results from an unbalanced unidirectional blood flow through placental arteriovenous anastomoses, and the proportion is up to 15% of all monochorionic pregnancies [73]. Additional factors such as

Commonly diagnosed during routine second-trimester ultrasound scanning, its predicted peak in incidence is around 20-21 weeks of gestation [75]. The presentation is highly variable and the recipient twin may present circulatory overload and polycythemia, possibly leading to congestive heart failure and hydrops. Contrarily, the donor twin shows oliguria and oligohydramnios, as well as anemia and growth restriction. Acute unbalancement can also

Data shows that 17% of the overall twin's perinatal mortality and 50% of all perinatal deaths

TTTS is properly diagnosed after confirmation of monochorionic twin pregnancy in early sonography demonstrating T-sign. In late diagnosed cases, chorionicity is supposed when single placental mass and a thin intertwin membrane are seen [78]. Besides the confirmation of a monochorionic diamniotic gestation, the presence of oligohydramnios (maximal vertical pocket <2 cm) within the donor sac, instead of polyhydramnios (maximal vertical pocket >8 cm) in the recipient sac are also essential [74, 77]. Differential diagnoses include selective

Additional sonographic findings usually coexist with TTTS such as significant growth discordance, absent or reversed a-wave in the ductus venous and velamentous cord insertion [74]. TTTS frequently occurs acutely and a meticulous follow-up in a specialized center is strongly recommended. The initial ultrasound assessment should include detailed anatomy scan and Doppler study, along with cervical length measurement. Fetal echocardiography is

In cases of sudden TTTS aggravation, acute polyhydramnios develops between 16 and 24 weeks. Mortality rates are high, reaching 80 to 100% in untreated disorders. There is also high

intrauterine growth restriction and other causes of amniotic fluid abnormalities [77].

vasoactive hormones are also believed to influence the development of TTTS [74].

**9. Monochorionic twin pregnancies specific complications**

tively discussed along the chapter.

214 Contemporary Gynecologic Practice

**9.2. Diagnostic criteria**

**9.3. Severity staging**

**9.1. Twin-Twin Transfusion Syndrome (TTTS)**

occur at any time before birth, threatening the prognosis [76].

in monochorionic diamniotic twins are attributed for TTTS [77].

a valuable option for cardiac function evaluation [75].

In order to improve the prognosis of TTTS, many options were proposed throughout the years, including specific strategies (selective fetoscopic laser coagulation of placental anastomoses) and non-specific strategies such as expectant management, amnioreduction, septostomy and selective reduction [75, 77]. An algorithm proposed by the Society for Maternal-Fetal Medicine for management of TTTS is shown in Figure 6 [77].

**Selectivefetoscopiclaserphotocoagulation:** first-line treatment for early-onset severe TTTS, requiring highly qualified professionals and specific equipment [75]. Advances in endoscop‐ ic surgery allowed proper identification of arteriovenous anastomoses and its coagula‐ tion. The rate of survival of at least one fetus is close to 75% and almost 40% of both twins. The overall frequency of neurological impairment is around 4% [81]. This procedure is only performed in severe stages and requires specialized tertiary center, trained staff, and adequate equipment. Maternal morbidity is minimal and complications include miscar‐ riage, preterm premature rupture of membranes, placental abruption, and stillbirth. The Eurofetus trial showed significantly higher survival rate of at least one fetus when comparing laser photocoagulation with amnioreduction (76% vs. 56%) as well as lesser neurological abnormalities (31% vs. 52%) [82].

**Amnioreduction:** progressive polyhydramnios in TTTS increases the risk of preterm prema‐ ture rupture of membranes and preterm birth, often causing maternal distress. The rationale is to temporary relieve intrauterine pressure. Serial amnioreduction is usually required, with an average of three procedures until the pregnancy reaches an acceptable gestational age [83]. Complications are similar to fetoscopy, although less frequent and with decreased maternal morbidity. Mean survival rate is 40-50% of at least one fetus and 20% for both. Reported neurological sequels are just about 20 to 30% [84]. The main advantage is that amnioreduction is inexpensive, easy to perform and widely available [74].

**Septostomy:** performed to balance the amniotic fluid amount in both sacs by needle-opening the intertwin membrane. It relieves cameras pressure and may be performed during amnior‐ eduction, with 40 to 83 % survival rate. Septostomy increases the risk of severe complications like cord entanglement and eventual disruption of the membrane. [85]. This procedure has generally been abandoned [75, 77].

**Selectivereduction:** therapeutic option through cord coagulation in order to improve the outcome of the surviving twin whenever there is an imminent risk of spontaneous intrauterine death of one fetus. It can be performed either by ultrasound guided vascular embolization or cord clamping through fetoscopy. A maximum of 50% survival is reached and most services have not supported this technique [86].

MCDA: monochorionic diamniotic; MVP: maximum vertical pocket; UA: umbilical artery

**Figure 6.** Algorithm for management of TTTS. Adapted from American Journal of Obstetrics and Gynecology, *LynnSimpson* [77], with permission from the publisher.
