Fetal blood sampling

Overview: We sought to review indications, technical aspects, risks and recommendations for fetal blood sampling (FBS).

Definition: Fetal blood sampling, also know as cordocentesis or percutaneous umbilical cord blood sampling, involves inserting a needle to gain access into the fetal circulation.  It allows the operator so sample or transfuse blood, or other blood products such as platelets, infect medication, or collect specimens for analysis of fetal health and disease. 

Epidemiology/Incidence: There are a variety of indications for FBS, and these indications have changed over the years. The advent of new, less invasive testing modalities and development of molecular genetic techniques has led to a decrease in the utilization of FBS.  While there is a paucity of literature on the true incidence of FBS, data collected from 21 member centers of the North American Fetal Therapy Network from 2006-2011 reported an average of 13 FBS procedures per center per year (unpublished data).

Indications for FBS: Suspected severe fetal anemia is the most common current indication for FBS in the United States. Direct measurement of fetal hemoglobin and confirmation of fetal anemia can only be made by FBS.  Anemia may be suspected due to presence of maternal alloantibodies, maternal parvovirus exposure or infection, other viral infections, or due to ultrasound findings such as fetal hydrops or elevated peak systolic velocity of the fetal middle-cerebral artery by Doppler studies (ref 14). FBS has played a large role in the management of Neonatal alloimmune thrombocytopenia (NAIT).  Currently, maternal intravenous immunoglobulin, sometimes in conjunction with corticosteroids, is administered to increase the fetal platelet count. While FBS is used in some circumstances to asses the response to this treatment, some experts believe that if maternal therapy is already being administered and vaginal delivery in not being considered, FBS may not add significant information to change management. Table 1 lists current and historic or less common indications for FBS.

Technical aspects of FBS: Currently, there are several ways to accomplish ultrasound-guided placement of a needle into the fetal circulation: directly into the umbilical cord (either at the placental cord insertion (PCI) or abdominal cord insertion (ACI) or into a free loop);into the intrahepatic portion of the umbilical vein (also called the intrahepatic vein (IHV)); or into the fetal heart (cardiocentesis).  Table 2 summarizes technical aspects as reported by some of the largest series, including data on use of maternal sedation, local anesthesia, ultrasound technique, puncture site and necessity to confirm fetal blood. A condensed summary of suggestions, adapted from Table 3:

• Insufficient data to recommend prophylactic antibiotics 
• Maternal sedation is used infrequently
• Local anesthesia is used by some centers
• Both needle guide instrument and freehand techniques are acceptable and should be performed under continuous ultrasound guidance
• A 20- or 22-gauge needle is commonly used, but may vary based on indication for procedure and other technical factors
• The preferred sampling site is the umbilical vein, either at PCI or ACI, or into free loop. Other sites include IHV and fetal hearto Paralytic agents preferred are pancuronium, atracurium or vecuronium.

Procedure-related risks of FBS: The most common procedure-related risk is bleeding from the umbilical cord puncture site (20-30%) and is usually self-limited  unless thrombocytopenia is also present. Other complications include bradycardia (5-10%) although the majority resolve within 5 minutes and usually do not require intervention (ref 64).  The risk of fetal loss after FBS (defined as loss/fetal demise within 2 weeks post-procedure) in a structurally normal fetus is estimated at 1% (ref 65,66). Higher loss rates are seen with fetuses with structural abnormalities, severe growth restriction or hydrops (7%,14%, and 25%, respectively) (ref 65).

Recommendations for fetal blood sampling (see Table 5):

• When invasive testing is planned for suspected severe fetal anemia or thrombocytopenia, we recommend FBS as procedure of choice, with availability of immediate transfusion if confirmed (Grade 1C)
• We recommend against the use of FBS for indications in which other less invasive, and therefore lower risk, alternatives are available (Grade 1C)
• We recommend counseling patients about the potential risk of FBS that may include, but may not be limited to: bleeding from puncture site;fetal bradycardia;pregnancy loss: and potential vertical transmission of hepatitis or HIV (Grade Best Practice)
• We recommend that FBS be performed by experienced operators at centers with expertise in invasive fetal procedures when feasible (Grade Best Practice)

Last Reaffirmed: Aug 1, 2022