Percutaneous umbilical blood sampling (PUBS), or cordocentesis, is an ultrasound-guided intrauterine procedure to obtain access to the fetal circulation for diagnostic and potentially therapeutic interventions.
The most common indication for PUBS is to diagnose and treat severe fetal anemia.1 Other indications include nonimmune hydrops and neonatal thrombocytopenia.
SPECIAL CONSIDERATIONS FOR PUBS
Bigelow and coauthors performed a single-center retrospective study which demonstrated that the average gestational age at the time of PUBS was 26.7 weeks, with 34.7% of cases performed before 24 weeks of gestation.2
Most centers use 20- or 22-gauge spinal needle under ultrasound guidance for access.
The most commonly accessed site is the umbilical vein at the placental cord insertion site. Other sites include the umbilical vein at the abdominal cord insertion site, free loop of the umbilical vein, intrahepatic vein, and the fetal heart.1
If intrauterine transfusion or a longer procedure time is expected, some centers use intravenous paralytics administered to the fetus to reduce fetal movement. Historically the use of pancuronium was more common; however, a double blinded study has found that atracurium (0.4 mg/kg) has less effect on fetal heart rate comparing to pancuronium (0.1 mg/kg).3 Pancuronium is the drug of choice by the proceduralists at the authors’ institution when muscle relaxant is needed. Rocuronium, one of the most widely used paralytics in the United States, has not been described in literature in PUBS.
RISKS AND COMPLICATIONS OF PUBS
Bleeding from the puncture site (20% to 30%), usually self-limiting.1
Fetal bradycardia (5% to 10%), usually resolves within 5 minutes.1 This could be due to vasospasm of the umbilical artery, streaming of blood from the umbilical vein to the umbilical artery, compression from a cord hematoma, etc.4 Prolonged fetal bradycardia may necessitate emergent cesarean delivery or result in fetal loss.
Incidence of pregnancy loss (within 2 weeks of procedure) varies. For fetuses without structural abnormalities or hydrops, the incidence is low (about 1%); for fetuses with hydrops especially nonimmune hydrops, the incidence is higher (10% to 30%).1
Currently, there is no data regarding the preferred anesthesia technique for PUBS. The Society of Maternal-Fetal-Medicine recommends that when fetal viability is reached, PUBS should be performed near or within an operating room in case an emergent cesarean delivery (the incidence of which is rare and not well documented) is indicated.1 Parturients over 24 weeks gestational age and who are pregnant with structurally abnormal fetuses may benefit from regional anesthesia. The anesthesiologists should assess patients on a case-by-case manner and be prepared for stat cesarean deliveries. If intrauterine transfusion and longer procedure time is anticipated, combined spinal and epidural anesthesia should be considered.