**10. Selective Intrauterine Growth Restriction (sIUGR)**

#### **10.1. Causes**

**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

**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

**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

is inexpensive, easy to perform and widely available [74].

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

*LynnSimpson* [77], with permission from the publisher.

**Figure 6.** Algorithm for management of TTTS. Adapted from American Journal of Obstetrics and Gynecology,

generally been abandoned [75, 77].

216 Contemporary Gynecologic Practice

have not supported this technique [86].

Selective intrauterine growth restriction (sIUGR) happens in 10% of monochorionic gestations, similar to dichorionic twins. It is diagnosed when the fetal weight of one twin is under the 10th percentile, and frequently there is 25% of discordance. In most cases the origin is in the placental territory discrepancy. Vascular anastomoses between both fetuses intrinsically justify IUGR, and one twin receives better-oxygenated blood [90].

#### **10.2. Classification**

Although a wide spectrum of vascular anastomoses variations establish different standards for fetal growth, three known patterns of umbilical artery dopplervelocimetry are inclined to develop sIUGR. Type I shows normal diastolic flow in this artery. Constantly absent or reverse flow characterizes type II. Finally, in type III, absent or reverse flow appears intermittently [91].

Prognosis is quite better in type I, contrasting with types II and III, which have been associated to an increased risk of neurological disorders, preterm births and stillbirths. In type III, massive blood transfusion through arterioarterial anastomoses is usually identified [91].

#### **10.3. Differential diagnosis between TTTS and early sIUGR**

In spite of the available evidence, causes of severe weight discordance in monochorionic pregnancies are still challenging for proper identification. Differential diagnosis demands early sonographic scanning, along with the exclusion of fetal abnormalities. The development of TTTS is probable once detected any abnormality in the amniotic volume with the larger compartment over 8 cm in one fetus cavity and bellow 2 cm in the other's.. If there is no disturb of the amniotic fluid and either the estimated weight of one twin is below the 10th percentile, or the weight discordance is over 25%, sIUGR may be presumed. Additionally, the evaluation of peak systolic velocity in the middle cerebral artery can be helpful. Finally, if not fitting any of the above criteria, a thorough follow up is recommended [91].

#### **10.4. Management**

Type I sIUGR has better prognosis and expectant management is reasonable until 34-35 weeks. Types II and III are associated with worse prognosis, and the therapeutic choice largely depends on the gestational age and severity staging. In these cases, laser therapy and cord occlusion may be practicable alternatives [91].

A fetal medicine specialist must follow monochorionic twins with routine sonographic assessment starting from 16 weeks. Finding any discordance in amniotic fluid or fetal weight, weekly interval is strongly recommended. Except for these cases, monochorionic gestations are expected to undergo an elective resolution around 37 weeks [91].

In our department, types II and III of sIUGR are closely monitored until 26 weeks of gestation, when the patient should be admitted at the hospital for daily Doppler ultrasound scanning, biophysical profile and cardiotocographic exam.

#### **10.5. Twin reversed arterial perfusion sequence (trap sequence)**

Twin reversed arterial perfusion sequence is a rare malformation in monochorionic pregnan‐ cies. The reported incidence is of 1:35000 deliveries and 1:100 monochorionic gestations. Usually, there are multiple structural abnormalities in one of the fetus, varying from a rudimentary heart to its complete absence, and an undeveloped head, associated or not to upper limbs alterations [92].

Generally an edema of the fetal trunk is observed or seen as an amorphous mass. A specific angioarchitecture characterized by an arterioarterial and a venovenous anastomosis supports the development of the acardiac twin. The normal twin acts like an infusion pump, with an increased mortality rate of 50 to 70%. Furthermore, this fetus is threatened by a raised risk of congestive cardiac failure, preterm labor, preterm premature rupture of membranes, prema‐ ture delivery, polyhydramnios and intrauterine fetal death [75, 93].

Therapeutic options include expectant management, which showed good results when associated to thorough vitality surveillance [94]. There are also invasive procedures to interrupt blood flow to the acardiac twin. Innumerous surgical approaches have been descri‐ bed such as endoscopic cord ligation or compression, bipolar or laser coagulation of the umbilical cord, radiofrequency ablation or even embolization of the vessels inside the abdo‐ men of the acardiac fetus. Despite the success of various techniques, intrafetal ablation is recommended as the best choice concerning its simplicity, safety and effectiveness when compared to others [95].

#### **10.6. Conjoined twins and abnormal variations**

early sonographic scanning, along with the exclusion of fetal abnormalities. The development of TTTS is probable once detected any abnormality in the amniotic volume with the larger compartment over 8 cm in one fetus cavity and bellow 2 cm in the other's.. If there is no disturb of the amniotic fluid and either the estimated weight of one twin is below the 10th percentile, or the weight discordance is over 25%, sIUGR may be presumed. Additionally, the evaluation of peak systolic velocity in the middle cerebral artery can be helpful. Finally, if not fitting any

Type I sIUGR has better prognosis and expectant management is reasonable until 34-35 weeks. Types II and III are associated with worse prognosis, and the therapeutic choice largely depends on the gestational age and severity staging. In these cases, laser therapy and cord

A fetal medicine specialist must follow monochorionic twins with routine sonographic assessment starting from 16 weeks. Finding any discordance in amniotic fluid or fetal weight, weekly interval is strongly recommended. Except for these cases, monochorionic gestations

In our department, types II and III of sIUGR are closely monitored until 26 weeks of gestation, when the patient should be admitted at the hospital for daily Doppler ultrasound scanning,

Twin reversed arterial perfusion sequence is a rare malformation in monochorionic pregnan‐ cies. The reported incidence is of 1:35000 deliveries and 1:100 monochorionic gestations. Usually, there are multiple structural abnormalities in one of the fetus, varying from a rudimentary heart to its complete absence, and an undeveloped head, associated or not to

Generally an edema of the fetal trunk is observed or seen as an amorphous mass. A specific angioarchitecture characterized by an arterioarterial and a venovenous anastomosis supports the development of the acardiac twin. The normal twin acts like an infusion pump, with an increased mortality rate of 50 to 70%. Furthermore, this fetus is threatened by a raised risk of congestive cardiac failure, preterm labor, preterm premature rupture of membranes, prema‐

Therapeutic options include expectant management, which showed good results when associated to thorough vitality surveillance [94]. There are also invasive procedures to interrupt blood flow to the acardiac twin. Innumerous surgical approaches have been descri‐ bed such as endoscopic cord ligation or compression, bipolar or laser coagulation of the umbilical cord, radiofrequency ablation or even embolization of the vessels inside the abdo‐ men of the acardiac fetus. Despite the success of various techniques, intrafetal ablation is recommended as the best choice concerning its simplicity, safety and effectiveness when

of the above criteria, a thorough follow up is recommended [91].

are expected to undergo an elective resolution around 37 weeks [91].

**10.5. Twin reversed arterial perfusion sequence (trap sequence)**

ture delivery, polyhydramnios and intrauterine fetal death [75, 93].

occlusion may be practicable alternatives [91].

biophysical profile and cardiotocographic exam.

upper limbs alterations [92].

compared to others [95].

**10.4. Management**

218 Contemporary Gynecologic Practice

The union of twins happens once in 50, 000 gestations, and it is related to imperfect segmen‐ tation of a single zygote after the 13th day of fecundation [96]. A marked female predominance of 72% is registered [97]. Diagnosis is held through early sonography in the first trimester [96]. Attachment may be rostral: omphalopagus, thoracopagus and cephalopagus; caudal: ischio‐ pagus; lateral: parapagus, or dorsal: craniopagus, rachipagus and pygopagus (Figure 7) [98].

**Figure 7.** The eight types of conjoined twins: **(1)** cephalopagus, **(2)** thoracopagus, **(3)** omphalopagus, **(4)** ischiopagus, **(5)** parapagus, **(6)** craniopagus, **(7)** pygopagus, **(8)** rachipagus. From Journal of Pediatric Surgery, *Rowena Spencer* [98], with permission from the publisher.

Prognosis is determined according to the site of attachment, organs involved, presence and extension of associated malformations. About 10% of conjoined twins are unequally distrib‐ uted and 50% have structural anomalies of major organs. Thus, planning for the best correction strategy requires knowledge of cardiac abnormalities, which are frequent in these cases. When a poor outcome is foreseen, vaginal delivery is preferable, although it depends on gestational week and fetuses' dimension [23, 96].

## **10.7. Externally attached parasitic twin**

Externally attached parasitic twin is also an infrequent finding in 1:1, 000, 000 births. They are asymmetric conjoined twins in whom a fetus with defect, or a fetal part, is externally attached in a relatively normal twin. Also known as heteropagus twins, it is believed that this type of union results from atrophic ischemia of monozygotic conjoined twins and the parasite twin depends on the cardiovascular system of the other. In most cases the parasite fetus does not have a functional heart or brain [96].

**Figure 8.** Epigastric heteropagus twins. **(A)** Adapted from Journal of Pediatric Surgery, *Sharma et al.* [97], with permis‐ sion from the publisher. **(B)** Adapted from Journal of Pediatric Surgery, *Ribeiro et al.* [99], with permission from the publisher.

#### **10.8. Fetus In Fetu (FIF)**

Fetus in fetu is a seldom finding in monochorionic twins, with incidence of 1:500, 000 deliveries. It has been also detected in adults. Even though already reported elsewhere, the most frequent localization is in the abdominal cavity. It is defined as a fetiform mass incorporated inside a host twin coming from abnormal embryogenesis [100].

FIF happens whenever there is an unequal division of totipotent cells of a blastocyst, resulting in the inclusion of a small cellular mass into a more mature embryo. The main sites of presen‐ tation by frequency order are vertebral column, limbs, central nervous system, digestive tract, vessels and genitourinary tract [101]. Karyotype is usually normal and surgery is encouraged to remove the included fetus, not only to relive its mass effect, but also considering its potential of malignization [100].

#### **10.9. Internal teratoma**

Prognosis is determined according to the site of attachment, organs involved, presence and extension of associated malformations. About 10% of conjoined twins are unequally distrib‐ uted and 50% have structural anomalies of major organs. Thus, planning for the best correction strategy requires knowledge of cardiac abnormalities, which are frequent in these cases. When a poor outcome is foreseen, vaginal delivery is preferable, although it depends on gestational

Externally attached parasitic twin is also an infrequent finding in 1:1, 000, 000 births. They are asymmetric conjoined twins in whom a fetus with defect, or a fetal part, is externally attached in a relatively normal twin. Also known as heteropagus twins, it is believed that this type of union results from atrophic ischemia of monozygotic conjoined twins and the parasite twin depends on the cardiovascular system of the other. In most cases the parasite fetus does not

**Figure 8.** Epigastric heteropagus twins. **(A)** Adapted from Journal of Pediatric Surgery, *Sharma et al.* [97], with permis‐ sion from the publisher. **(B)** Adapted from Journal of Pediatric Surgery, *Ribeiro et al.* [99], with permission from the

Fetus in fetu is a seldom finding in monochorionic twins, with incidence of 1:500, 000 deliveries. It has been also detected in adults. Even though already reported elsewhere, the most frequent localization is in the abdominal cavity. It is defined as a fetiform mass incorporated inside a

FIF happens whenever there is an unequal division of totipotent cells of a blastocyst, resulting in the inclusion of a small cellular mass into a more mature embryo. The main sites of presen‐ tation by frequency order are vertebral column, limbs, central nervous system, digestive tract, vessels and genitourinary tract [101]. Karyotype is usually normal and surgery is encouraged to remove the included fetus, not only to relive its mass effect, but also considering its potential

week and fetuses' dimension [23, 96].

220 Contemporary Gynecologic Practice

**10.7. Externally attached parasitic twin**

have a functional heart or brain [96].

publisher.

**10.8. Fetus In Fetu (FIF)**

of malignization [100].

host twin coming from abnormal embryogenesis [100].

Internal teratomas are rare congenital tumors, usually benign and of multifactorial etiology. They are constituted by a complex combination of microscopically identifiable tissues inside the fetus, which derivate from mesoderm, endoderm and ectoderm. In its interior, structures like teeth, intestine and hair are covered by connective tissue receiving vascularization from small vessels. It has independent potential of growth and also of malignization [96].

Although prenatal diagnosis can be held by a simple sonographic study within 15-16 weeks, tridimensional evaluation and the use of magnetic resonance may improve diagnostic precision, allowing the establishment of its precise localization, extension, and dissemination.
