Abstract
Advances in prenatal diagnosis, imaging, and surgical equipment have all contributed to the development of fetal surgery. Some fetal abnormalities are amenable to intrauterine fetal surgery, but the majority of anatomic malformations diagnosed in utero remain unsuitable for fetal intervention. Prenatal diagnosis of serious malformations (e.g., those that are uncorrectable and incompatible with normal postnatal life) allows the choice of pregnancy termination. Most correctable malformations are best managed after delivery, with antepartum recognition allowing time for the coordination of appropriate prenatal and postnatal care. Some defects, especially those that cause airway obstruction or irreversible end-organ damage, are suitable for intrapartum intervention. This allows the benefit of intervention while the uteroplacental unit remains functional and often eliminates any urgency that would be associated with undertaking the procedure in the postnatal period.
Guidelines for performing fetal surgery were originally developed more than 35 years ago but remain relevant today with only minimal modifications. All fetal interventions should undergo multidisciplinary deliberation and planning. Potential maternal risks should be discussed as part of the consent process and a detailed maternal preoperative evaluation completed to ensure minimal risk to the mother. Guidelines from the American College of Obstetricians and Gynecologists (ACOG) and the American Academy of Pediatrics (AAP) recommend that fetal treatment centers include a multidisciplinary comprehensive consent and counseling process, oversight of fetal research, and participation in a data-sharing fetal intervention network.
Keywords
Fetal surgery, Fetal anesthesia, EXIT procedure, Myelomeningocele, Intrauterine transfusion, Twin-to-twin transfusion syndrome, Congenital diaphragmatic hernia
Chapter Outline
Indications and Rationale for Fetal Surgery, 134
Fetal Anemia and Intrauterine Transfusion, 134
Obstructive Uropathy, 134
Congenital Diaphragmatic Hernia, 135
Congenital Pulmonary Airway Malformation, 137
Sacrococcygeal Teratoma, 137
Myelomeningocele, 138
Twin-to-Twin Transfusion Syndrome, 139
Twin Reversed Arterial Perfusion Sequence, 142
Congenital Heart Defects, 142
Surgical Benefits and Risks, 143
Anesthetic Management, 143
Anesthesia for Minimally Invasive and Percutaneous Procedures, 144
Anesthesia for Open Fetal Surgery, 144
Anesthesia for the Ex Utero Intrapartum Treatment Procedure, 146
Fetal Response to Surgical Stimulation, 147
Effects of Anesthesia on the Fetus, 148
Fetal Monitoring, 149
The Future of Fetal Therapy, 149
The ability to treat underlying fetal conditions with medical procedures or surgery is a relatively recent development. Fetal therapy originated in 1963 with Sir William Liley’s successful intraperitoneal blood transfusion to a fetus with erythroblastosis fetalis. In 1981, following sheep and primate studies, the first successful human fetal surgery, a vesicostomy, was performed in a fetus with bilateral hydronephrosis secondary to a lower urinary tract obstruction.
Advances in prenatal diagnosis, imaging, and surgical equipment have all contributed to the development of fetal surgery. Some fetal abnormalities are amenable to intrauterine fetal surgery, but the majority of anatomic malformations diagnosed in utero remain unsuitable for fetal intervention. Prenatal diagnosis of serious malformations (e.g., those that are uncorrectable and incompatible with normal postnatal life) allows the choice of pregnancy termination. Most correctable malformations are best managed after delivery, with antepartum recognition allowing time for the coordination of appropriate prenatal and postnatal care. Some defects, especially those that cause airway obstruction or irreversible end-organ damage, are suitable for intrapartum intervention. This allows the benefit of intervention while the uteroplacental unit remains functional and often eliminates any urgency that would be associated with undertaking the procedure in the postnatal period.
Guidelines for performing fetal surgery ( Box 7.1 ) were originally developed more than 35 years ago but remain relevant today with only minimal modifications. All fetal interventions should undergo multidisciplinary deliberation and planning. Potential maternal risks should be discussed as part of the consent process and a detailed maternal preoperative evaluation completed to ensure minimal risk to the mother. Guidelines from the American College of Obstetricians and Gynecologists (ACOG) and the American Academy of Pediatrics (AAP) recommend that fetal treatment centers include a multidisciplinary comprehensive consent and counseling process, oversight of fetal research, and participation in a data-sharing fetal intervention network.
- 1.
Accurate diagnosis and staging is possible.
- 2.
Other anomalies that would contraindicate fetal intervention are excluded.
- 3.
Progression, severity, and prognosis of the condition are understood.
- 4.
No effective postnatal therapy is currently available, and if not treated before birth, the anomaly would result in fetal death, irreversible organ damage, or other severe postnatal morbidity.
- 5.
Intrauterine surgery has been proven feasible in animal models, with demonstrated reversal of the deleterious effects of the condition.
- 6.
The maternal risk is acceptably low.
- 7.
Interventions are performed in specialized multidisciplinary fetal treatment centers within strict protocols and approval of the local ethics committee, with informed consent obtained from the mother or parents.
- 8.
There is access to high-level specialized medical care, including bioethical and psychosocial care and counseling.
Fetal surgical interventions can be broadly categorized into three kinds of procedures, namely, minimally invasive procedures, open surgical procedures, and intrapartum procedures. A summary of fetal conditions, therapy, and intervention is detailed in Table 7.1 .
| Fetal Condition | Therapy Rationale | Type | Intervention |
|---|---|---|---|
| Fetal anemia or thrombocytopenia | Prevention of heart failure and fetal hydrops | Fetal image guided | Intrauterine transfusion |
| Aortic stenosis, intact atrial septum, or pulmonary atresia | Prevention of fetal hydrops, myocardial dysfunction, and hypoplastic left (and right) heart | Fetal image guided | Percutaneous fetal valvuloplasty or septoplasty |
| Obstructive uropathy | Bladder decompression with reduction in renal dysfunction, pulmonary hypoplasia, oligohydramnios, and limb malformation | Fetal image guided or fetoscopy | Percutaneous vesicoamniotic shunting or fetoscopic laser ablation of urethral valves |
| Twin reversed arterial perfusion sequence | Prevention of high-output cardiac failure in the normal twin by stopping flow to the acardiac twin | Fetal image guided or fetoscopy | Umbilical radiofrequency ablation or fetoscopic cord coagulation |
| Twin-to-twin transfusion syndrome | Reduction of twin-to-twin blood flow and prevention of cardiac failure | Fetoscopy | Fetoscopic laser photocoagulation of placental vessels and/or amnioreduction |
| Congenital diaphragmatic hernia | Prevention of pulmonary hypoplasia | Fetoscopy | Fetoscopic tracheal occlusion |
| Myelomeningocele | Reduction in hydrocephalus and hindbrain herniation with improved neurologic function | Open | Closure of fetal defect in utero |
| Sacrococcygeal teratoma | Prevention of high-output cardiac failure, hydrops, and polyhydramnios | Fetal image guided or open | Ablation of tumor vasculature or open fetal tumor debulking |
| Congenital cystic adenomatoid malformation | Reversal of pulmonary hypoplasia and cardiac failure | Fetal image guided or open | Thoracoamniotic shunting or open fetal lobectomy |
| Fetal airway compression | Secured airway and/or circulatory support to prevent respiratory compromise at birth | Open intrapartum | Ex utero intrapartum therapy that allows stabilization while on uteroplacental circulation |
Minimally invasive procedures involve either fetoscopic or image-guided percutaneous procedures, typically performed near mid-gestation. They entail a lower risk for preterm labor and delivery than open procedures because they do not require a hysterotomy, yet the risk for preterm premature rupture of membranes (PROM) remains.
Open surgical procedures involve both a maternal laparotomy and hysterotomy with use of pharmacologic agents to maintain uterine relaxation. These procedures are typically performed near mid-gestation and entail greater maternal and fetal risks compared with the minimally invasive techniques, including a significant risk for preterm PROM, preterm labor and delivery, uterine dehiscence, oligohydramnios, hemorrhage, pulmonary edema, and fetal mortality. In addition, after an open surgical procedure, a cesarean delivery is required for the pregnancy and all future deliveries owing to the location of the hysterotomy and the associated risks for uterine dehiscence or rupture.
The third kind of procedure involves a modification of cesarean delivery to allow intrapartum fetal therapy while the fetus remains supported by placental gas exchange. These delivery techniques are termed ex utero intrapartum therapy (EXIT) procedures . EXIT procedures are most often employed in order for gas exchange to continue across the placenta (placental bypass) while (1) securing the airway by endotracheal intubation, bronchoscopy, or tracheostomy in fetuses with congenital airway obstruction or neck mass or (2) performing invasive fetal procedures required before delivery. The EXIT procedure enables the prevention of asphyxia in neonates in whom securing an airway after birth can be problematic. The procedure can also be used as a bridge to extracorporeal membrane oxygenation (ECMO) for a fetus with cardiopulmonary disease at risk for postnatal cardiac failure or failure of adequate pulmonary gas exchange.
Indications and Rationale for Fetal Surgery
Fetal Anemia and Intrauterine Transfusion
The rate of fetal anemia secondary to rhesus D (RhD) sensitization has decreased to 1 in 1000 pregnancies following the use of RhD immunoglobulin prophylaxis. Fetal anemia can occur secondary to other red cell antigens, viral infections, homozygous thalassemia, maternal-fetal hemorrhage, and placental chorioangiomas. Serial Doppler studies of the middle cerebral artery (MCA) peak velocity are used to diagnose fetal anemia. A sample of fetal umbilical cord blood just before starting the intrauterine transfusion (IUT) is the most accurate test for fetal anemia. Before 18 weeks’ gestation, intraperitoneal transfusion may be chosen for treatment of fetal anemia given that accessing the umbilical vein may not be possible. In this procedure, donor red blood cells are injected into the fetal peritoneal cavity and transported through the lymphatic system to the fetal circulation. With early diagnosis of severe cases, combining these two procedures with immunoglobulin therapy may provide added benefit.
IUTs are frequently performed using a 20- or 22-gauge needle with local anesthesia at the needle insertion site. The needle is inserted percutaneously through the maternal abdomen and uterus under ultrasonographic guidance to access the umbilical vein ( Fig. 7.1 ). The cord is often accessed near its placental insertion for stability, but a loop of umbilical cord or an intrahepatic portion of the cord can also be used. The volume of O-negative, cytomegalovirus (CMV)-negative, irradiated, leukocyte-depleted, packed red blood cells is determined based on the estimated fetal weight, gestational age, autologous hemoglobin, and hemoglobin of the sampled fetal blood. Following an IUT, the fetal hemoglobin levels slowly decrease, and multiple IUTs are often required at 1- to 3-week intervals. Although the umbilical cord does not have pain receptors, if the needle is advanced into the fetus for intrahepatic vascular access, a fetal stress response will occur; fentanyl or another opioid should be administered to blunt this response. An intramuscular paralytic agent can be administered to the fetus to decrease the chance of fetal movement dislodging the transfusion needle or sheering the cord vasculature. Providers should be prepared for a possible emergent cesarean delivery at any point during the IUT if the fetus is of viable age. Rates of fetal demise following IUT range from 1% to 5%. Increased risk for fetal demise is associated with fetal hydrops, early gestational age, not using fetal paralysis, operator inexperience, and severity of fetal anemia. Other complications include transient fetal bradycardia (8%), emergent cesarean delivery (2%), intrauterine infection (0.3%), and rupture of membranes (0.1%).
Obstructive Uropathy
Lower urinary tract obstruction (LUTO) occurs in approximately 1 in 5000 live births. Congenital bilateral hydronephrosis results from fetal urethral obstruction at the bladder outlet, most commonly by either posterior urethral valves (typically male fetuses) or urethral atresia. Other causes of fetal obstructive uropathy include obstruction at the ureteropelvic or vesicoureteric junction and a number of complex disorders in females (e.g., cloacal plate anomalies). These uropathies are typically evaluated by ultrasonography, which is often performed to investigate oligohydramnios from diminished fetal urine output. Magnetic resonance imaging (MRI) can also be used, but there is no evidence that it is superior. LUTO may lead to progressive renal dysplasia and dysfunction, bladder distention, and oligohydramnios, and ultimately result in devastating developmental consequences, such as limb and facial deformities, pulmonary hypoplasia, and even neonatal death ( Fig. 7.2 ). A disease severity classification system for LUTO based primarily on amniotic fluid index, renal imaging, and urinary biochemistries has recently been proposed. Although postnatal correction relieves the obstruction, 25% to 30% of survivors develop end-stage kidney disease requiring dialysis by 5 years of age. Early intrauterine intervention with placement of a vesicoamniotic shunt (VAS) allows drainage of urine from the fetal bladder into the amniotic cavity, thereby decompressing the urinary tract. In animal models, intrauterine relief of obstructive uropathy improves dysplastic renal histology, restores normal urine flow and amniotic fluid volume, and results in improved lung growth and development.
A VAS is a valveless, double-coiled catheter placed percutaneously with ultrasonographic guidance, with one coil remaining in the urinary bladder and the other in the amniotic space. Common problems associated with these catheters include: (1) difficult placement, occlusion, and displacement; (2) fetal trauma, iatrogenic abdominal wall defects, and amnioperitoneal leaking; and (3) preterm PROM, preterm labor, and chorioamnionitis. In a recent meta-analysis of studies between 1990 and 2015, there was a perinatal survival improvement with VAS compared with conservative management (57.1% versus 38.8%, P < .01). However, there was no difference in 2-year survival or postnatal renal function. A large multicenter, randomized controlled trial comparing the perinatal mortality and renal function of fetuses with LUTO treated by either VAS or conservative care suggested improved survival in fetuses receiving VAS treatment, but was unfortunately closed early secondary to poor enrollment.
Fetal cystoscopy is a more recent treatment in which a trocar-assisted fetoscope enters the fetal bladder under ultrasonographic guidance and allows direct visualization of the fetal urethra. Although not a viable treatment for urethral atresia, fetal cystoscopy facilitates diagnosis and treatment of LUTO caused by posterior urethral valves (PUVs). Once visualized, the PUVs are destroyed using guide wires and hydroablation or laser ablation. A two-center case-control study compared fetal cystoscopy ( n = 34) with VAS ( n = 16) and no intervention ( n = 61) for cases between 1990 and 2013. Both fetal cystoscopy and VAS improved the 6-month survival rate in severe LUTO. Compared with no intervention, a trend for normal renal function was present in the fetal cystoscopy group ( P = .06) but not in the VAS group ( P = .33). In just the subset of PUV cases ( n = 57), fetal cystoscopy improved both 6-month survival and renal function, while VAS was only associated with improvement in the 6-month survival rate.
Current evidence supports the use of fetal intervention for LUTO in selected fetuses in an effort to restore amniotic fluid volume, prevent pulmonary hypoplasia, and decrease perinatal mortality. However, the effects on long-term renal function, bladder function, and other morbidities remain unclear.
Congenital Diaphragmatic Hernia
Approximately 1 in 2500 live-born infants has a congenital diaphragmatic hernia (CDH). Without fetal intervention, this anomaly causes significant morbidity and mortality from pulmonary hypoplasia and insufficiency. Survival rates have improved to greater than 70% over the past 25 years and are closely associated with the degree of pulmonary hypertension and respiratory insufficiency. Significant mortality occurs despite optimal postnatal surgical management at tertiary care medical centers (i.e., procedures involving removal of the herniated viscera from the chest, administration of surfactant, ventilation techniques that minimize lung trauma, use of ECMO, and closure of the diaphragm). Intrauterine correction of CDH has the potential to prevent pulmonary hypoplasia and allow the fetal lung to develop before delivery.
Fetal lamb models of CDH demonstrated that parenchymal hypoplasia and associated pulmonary vascular changes could be reversed by correction in utero. Primary open repairs of human CDH in utero have been undertaken only for fetuses with severe disease, with limited success but many lessons learned, including the development of minimally invasive approaches.
Fetal lungs contribute to amniotic fluid volume by secreting more than 100 mL/kg/day of fluid that exits the trachea and mouth. Tracheal occlusion impedes the normal egress of fetal lung fluid and results in expansion of the hypoplastic lung, thereby inducing lung growth and cellular maturation in fetuses with CDH. This occlusion technique, termed “ p lug the l ung u ntil it g rows” (i.e., PLUG), replaced primary repair in utero for the correction of the pulmonary hypoplasia associated with CDH. It is a less extensive, palliative fetal surgical procedure that enhances lung growth to improve postnatal survival, with postponement of the definitive repair until after birth. Once the trachea is occluded, fetal pulmonary fluid slowly accumulates and expands the lung, pushing the viscera out of the thorax. A small detachable balloon for endoluminal tracheal occlusion is placed in the trachea via percutaneous endoscopic endotracheal intubation and is either left in place until delivery or deflated earlier ( Fig. 7.3 ).
A prospective randomized trial (1999–2001) evaluated fetal tracheal occlusion for intrauterine treatment of severe CDH. Inclusion criteria included (1) a gestational age of 22 to 28 weeks, (2) left-sided herniation of the liver into the hemithorax, and (3) a low lung-to-head ratio (LHR) (i.e., < 1.4). The LHR is a ratio of the contralateral lung cross-sectional area compared with head circumference and is correlated with the severity of pulmonary hypoplasia and survival for a given gestational age. The trial was closed early ( n = 11). Fetal tracheal occlusion resulted in no improvement in survival compared with the control group (77% versus 73%) and no reduction in morbidity at 90 days. The rates of preterm PROM and preterm delivery were higher in the fetal intervention group. However, the survival rate was unexpectedly high in the control group. It is speculated that the LHR criterion of less than 1.4 was not sufficiently restrictive and allowed inclusion of fetuses in the study that were likely to survive with standard postnatal tertiary medical care. Table 7.2 notes improved survival for left-sided CDH fetuses treated in utero with an LHR < 1.0 compared with standard postnatal care.
| LHR (mm) a | POSTNATAL MANAGEMENT | FETOSCOPIC TRACHEAL OCCLUSION | ||
|---|---|---|---|---|
| Number of Fetuses | Survival Number (%) | Number of Fetuses | Survival Number (%) | |
| 0.4–0.5 | 2 | 0 | 6 | 1 (16.7) |
| 0.6–0.7 | 6 | 0 | 13 | 8 (61.5) |
| 0.8–0.9 | 19 | 3 (15.8) | 9 | 7 (77.8) |
| 1.0–1.1 | 23 | 14 (60.8) | ||
| 1.2–1.3 | 19 | 13 (68.4) | ||
| 1.4–1.5 | 11 | 8 (72.7) | ||
| ≥ 1.6 | 6 | 5 (83.3) | ||
| Total | 86 | 43 (50) | 28 | 16 (57.1) |
a LHR measurements in the table were obtained at 23 to 29 weeks’ gestation.
Use of fetal endoscopic tracheal occlusion (FETO) began to focus on more severe cases of CDH with a high risk for death. FETO intervention criteria for fetuses at high risk included both an LHR less than 1.0 and liver herniation into the hemithorax. Owing to concern for tracheal damage by very early tracheal balloon placement, the tracheal balloon is placed between 26 and 28 weeks’ gestation and removed before birth by a second fetoscopic procedure near 34 weeks’ gestation (if the fetus is still in utero ). This second procedure is performed to minimize the risk for preterm labor, avoid the need for the EXIT procedure (discussed later in the chapter), and possibly improve lung growth and minimize the reduction of type II alveolar cells associated with prolonged tracheal occlusion. Recently, a single institution, prospective observational cohort study compared treatment of left-sided severe CHD (LHR < 1.0 and liver herniation) with FETO to historic controls. The FETO group had mean balloon placement and removal at 28 and 34 weeks’ gestation, respectively. The FETO group had increased 2-year survival (67% versus 11%) and reduced need for ECMO. A recent meta-analysis examined five trials published between 2004 and 2012 that compared FETO to contemporary controls. All studies included isolated severe CDH with an LHR ≤ 1.0 and liver herniation into the thorax. Survival outcome was improved with FETO (odds ratio 13). In all these studies, it is possible that the comparative results may represent selection bias or improvements in technique and clinical care over time. Although promising, there is currently inadequate evidence to recommend intrauterine fetal intervention to treat CDH as a routine clinical practice.
In 2009, a randomized Tracheal Occlusion to Accelerate Lung growth trial (TOTAL) was started. It compares postnatal CDH management to both late (30 to 32 weeks’ gestation) FETO intervention for moderate lung hypoplasia and also earlier FETO intervention (27 to 30 weeks’ gestation) for severe lung hypoplasia. In both arms of the TOTAL trial, the balloon is removed in the 34th week of gestation. In addition, it is now appreciated that LHR depends on gestational age and that a ratio of observed to expected LHR is a better expression of CDH severity and likelihood of survival. This ratio is used as part of the ongoing TOTAL trial. Results of this trial will help determine if FETO should be offered and whether there is an optimal gestational age to intervene.
Congenital Pulmonary Airway Malformation
Congenital pulmonary airway malformations (CPAMs) are pulmonary tumors with cystic and solid components usually isolated to a single lung. These malformations were previously described as congenital cystic adenomatoid malformations (CCAMs). The incidence is approximately 1 in 25,000 pregnancies. A second-trimester ultrasonogram is reliable and accurate in detecting pulmonary lesions, with MRI and color Doppler ultrasonography facilitating differentiation between CPAM, bronchopulmonary sequestration, bronchogenic cysts, neurogenic cysts, and CDH. The classification scheme for CPAM proposed by Stocker includes five subtypes, based on cyst size, characteristics of the epithelial lining, cyst wall thickness, and the presence of mucous cells, cartilage, and skeletal muscle. Lesions are assessed by ultrasonography and can be divided by the presence of cysts either larger (macrocystic) or smaller (microcystic) than 5 mm in diameter. Lesions can regress, resulting in minimal associated morbidity, or progressively enlarge, often resulting in fetal hydrops (fetal heart failure). The size and growth of the lesions, rather than their specific type, are the primary determinate of overall prognosis. Small lesions detected in utero or in the neonate are treated after birth by surgical excision of the affected pulmonary lobe. Large lesions can cause mediastinal shift, hydrops, polyhydramnios, and pulmonary hypoplasia and can interfere with fetal or neonatal survival. Fetuses with untreated lesions associated with hydrops have a survival rate of less than 5%. In a retrospective single-institution review of 71 cases, the initial antenatal ultrasonographic ratio of CPAM volume-to-fetal head circumference (congenital pulmonary airway malformation volume ratio [CVR]) was evaluated for hydrops formation and postnatal outcomes. Fetuses with a CVR less than 0.56 were noted to have no adverse postnatal outcomes, whereas a CVR greater than 0.56 had a positive predictive value for adverse postnatal outcomes of 33%. In addition, a CVR greater than 1.6 was associated with a greater risk for hydrops, and a CVR less than or equal to 1.6 with absence of a dominant cyst was associated with a < 3% risk for hydrops.
Depending on size, location, and other characteristics, CPAMs can be managed with either fetal intervention or postnatal resection. Macrocystic lesions can be decompressed in utero by thoracocentesis or placement of shunt catheters between the cystic area and the amniotic cavity, resulting in sustained decompression and resolution of hydrops. These in utero procedures are followed by postnatal surgery. However, not all lesions can be decompressed successfully with a shunt because the cysts are not always contiguous (i.e., in communication with each other) and can refill rapidly. In addition, thoracoamniotic shunts have associated risks, including malfunction, displacement, fetal hemorrhage, preterm PROM, preterm labor, and chorioamnionitis. In a series of 68 fetuses with macrocystic CPAMs treated with thoracoamniotic shunts, the overall survival rate was 68% in hydropic and 88% in nonhydropic fetuses. CPAMs inappropriate for drainage can be resected with open fetal surgery. Intrauterine pulmonary lobectomy for lesions associated with fetal hydrops has resulted in a 30-day postnatal survival rate of 50%, with tumor resection allowing for compensatory lung growth and resolution of hydrops. Additional, less common options include resection while on placental circulation (EXIT procedure) or on postnatal ECMO, radiofrequency or laser ablation, and percutaneous ultrasound-guided sclerotherapy. Maternal administration of betamethasone has been noted to improve fetal hydrops and overall outcome in selected fetuses with CPAM. Thoracoamniotic shunts have also been successfully placed to decompress massive congenital pleural effusions caused by fetal chylothorax that otherwise would result in hydrops fetalis, pulmonary compression, and fetal or neonatal death.
Sacrococcygeal Teratoma
With a prevalence of approximately 1 in 20,000 to 40,000, sacrococcygeal teratoma (SCT) is associated with perinatal demise in 25% to 37% of cases. Management of these tumors requires serial ultrasonographic assessments, as some undergo rapid, substantial growth (i.e., 1000 cubic centimeters), function as large arteriovenous fistulas, and result in high-output cardiac failure, hydrops fetalis, and placentomegaly. SCTs are staged using the Altman criteria, which focuses on their location. Stage I tumors are based entirely outside the pelvis and are suitable for intervention; by contrast, Stage IV tumors are completely within the pelvis and not amenable to fetal resection. Tumor size is estimated based on a tumor volume-to-fetal weight ratio, with large SCTs considered > 0.12 cm 3 /g ; rapid growth (>150 cm 3 /week) is associated with adverse outcomes, including tumor rupture and hemorrhage, as well as intrapartum dystocia. Fetuses with lesions diagnosed before 30 weeks’ gestation have a poor prognosis (< 7% survival) but may benefit from in utero intervention. Current surgical techniques do not allow complete resection of lesions that deeply invade the pelvis; however, in utero radiofrequency ablation, embolization, and thermocoagulation of the tumor or feeding vessels can reduce the tumor burden and resolve hydrops. Large multicenter studies are needed to determine which therapies deliver the most definitive, optimal benefits ( Fig. 7.4A ). During open fetal tumor resection ( Fig. 7.4B ), catheterization of a fetal limb or umbilical cord vein may be needed to allow for blood or fluid administration.
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