Therapeutic Obstetrical Procedures
26.1 Fetal Blood Transfusion
Description and Clinical Features
If a fetus is found to be anemic based on umbilical blood sampling, it can be treated with a blood transfusion. The most direct way to do so is to transfuse red blood cells into the umbilical vein. If the umbilical vein cannot be accessed, an alternative approach is to inject blood into the fetal peritoneal cavity, where the erythrocytes are absorbed into fetal circulation.
Continuous real-time guidance is essential for fetal blood transfusion. The most common transfusion site is the umbilical vein in the umbilical cord (Figure 26.1.1). If this cannot be accessed, an alternative site is the intrahepatic umbilical vein (Figure 26.1.2). When neither of these is accessible, the blood can be injected intraperitoneally (Figure 26.1.3). When monitoring an intravascular transfusion, the observation of streaming echoes in the umbilical vein confirms that the transfusion is proceeding appropriately (Figures 26.1.1 and 26.1.2). When monitoring an intraperitoneal transfusion, free fluid should be seen collecting in the fetal abdomen as the blood is injected.
26.2 Thoracentesis and Thoracoamniotic Shunting
Description and Clinical Features
Drainage of fetal pleural effusions may improve pregnancy outcome in a number of situations. Examples include the following:
Hydrops with a large unilateral pleural effusion: Drainage of the unilateral effusion may increase venous return to the fetal heart by correcting mediastinal shift, thereby improving or alleviating hydrops.
Large bilateral pleural effusions to permit lung growth: Drainage of large effusions provides space for the developing lungs to expand and grow, preventing pulmonary hypoplasia that may be life-threatening at birth.
Large bilateral pleural effusions in a fetus immediately before delivery: Bilateral thoracenteses, followed immediately by delivery, will allow the neonatal lungs to expand and obviate the need for emergency postnatal thoracenteses.
Fluid may be removed by thoracentesis, whereby a needle is inserted into the fetal thorax, fluid is aspirated, and the needle is removed.
In some cases with large effusions or those with hydrops, thoracentesis may provide only temporary improvement, after which the pleural effusion recurs. In such cases, the lungs will not have space to expand and grow or the hydrops will persist or worsen. In either of these situations, placing one or two thoracoamniotic shunts may be necessary, in order to provide continuous drainage of the pleural fluid.
Fetal thoracentesis is performed using real-time sonographic monitoring to guide a needle into the fetal thorax (Figure 26.2.1). Placement of a thoracoamniotic shunt involves several steps, all directed by ultrasound (Figure 26.2.2). First, a trocar (large-bore needle) with a sharp-tipped obturator filling the lumen is directed into the fetal thorax. The obturator is removed and a double-pigtail catheter is threaded through the trocar until one end of the catheter coils in the fetal thorax. The trocar is then pulled back until its tip is in the amniotic fluid, and the remaining part of the catheter is pushed out of the trocar into the amniotic cavity. The trocar is then withdrawn to complete the procedure.
Figure 26.2.1 Fetal thoracentesis. A needle (arrowheads), inserted percutaneously through the maternal anterior abdominal wall, ends in the thorax of a fetus with a large pleural effusion.
26.3 Bladder Drainage and Vesicoamniotic Shunting
Description and Clinical Features
Urethral obstruction, which is most commonly due to posterior urethral valves, is likely to cause life-threatening pulmonary hypoplasia from severe, prolonged oligohydramnios and renal dysplasia from urinary obstruction. Both of these serious complications of urethral obstruction can sometimes be treated in utero by ultrasound-guided percutaneous placement of a vesicoamniotic shunt, which provides relief of the urinary obstruction by allowing urine to flow from the bladder to the amniotic cavity, in the process replenishing amniotic fluid volume.
A fetus diagnosed with urethral obstruction must meet several criteria before a corrective procedure should be considered:
Oligohydramnios: In the absence of oligohydramnios, the prognosis is good without surgery because bladder outlet obstruction is incomplete.
Gestational age incompatible with viability outside the uterus.
No other major structural anomaly.
Renal parenchyma appears normal on ultrasound.
Adequate fetal renal function: If the above criteria are met, fetal renal function is evaluated by performing an ultrasound-guided fetal bladder drainage. The presence of normal fetal urinary electrolyte levels and reaccumulation of urine in the fetal bladder over the next 24 hours indicate adequate renal function.
If most or all these criteria are met, in utero treatment of the urethral obstruction should be contemplated.
Ultrasound plays a central role in all aspects of the diagnosis and treatment of urethral obstruction, including diagnosing the condition, assessing whether the fetus is a candidate for in utero intervention, guiding the drainage procedure, and guiding placement of the vesicoamniotic shunt. After urethral obstruction is established by ultrasound, ultrasound is used to assess the amniotic fluid volume, evaluate the fetal renal parenchyma for evidence of dysplasia (parenchymal cysts or thin echogenic cortex), conduct a comprehensive fetal anatomic survey to assess for coexisting anomalies, assign gestational age, and guide amniocentesis or umbilical blood sampling to determine fetal karyotype. If the assessment finds no contraindication to proceeding, ultrasound is then used to guide a needle into the fetal urinary bladder (Figure 26.3.1) to assess renal function.
When the decision is made to proceed with vesicoamniotic shunting, shunt placement is performed under ultrasound guidance (Figure 26.3.2). The procedure often begins with an amnioinfusion (reverse amniocentesis) involving instillation of saline into the amniotic space to create a pocket of fluid in which to place the amniotic end of the vesicoamniotic shunt. A large-bore needle (trocar) is then inserted into the fetal bladder and a double-pigtail catheter is inserted through the needle. One end of the catheter is advanced into the fetal bladder. The trocar is then withdrawn into the amniotic fluid, and the rest of the catheter is pushed out of the trocar, so that the second coil of the catheter is in the amniotic cavity. The trocar is then removed.
Once a shunt has been placed, the fetus should be monitored closely by ultrasound. If the shunt is working properly, the fetal bladder will remain decompressed. Redistention of the bladder indicates shunt malfunction, due either to debris clogging the shunt or to dislodgment of the shunt, which necessitates either delivery of the fetus or insertion of a new shunt.
Figure 26.3.1 Fetal bladder drainage. A: A needle (arrowheads) has been guided by ultrasound into a distended fetal bladder (*). B: After urine has been withdrawn through the needle (arrowheads), the bladder (*) is considerably smaller.
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