What is the technique for performing an intra‑uterine (intravascular) fetal blood transfusion?

Technique for Intrauterine (Intravascular) Fetal Blood Transfusion

Intrauterine transfusion should be performed using ultrasound-guided intravascular access to the umbilical vein, with a systematic approach involving pre-procedure preparation, precise needle placement, confirmation of intravascular access, calculated blood volume transfusion, and continuous fetal monitoring throughout the procedure. 1

Pre-Procedure Preparation

Team and Equipment Assembly

• Assemble a dedicated team including the primary operator, sonographer, and assistant to ensure coordinated execution 1
• Obtain maternal blood sample for comparison with fetal hematocrit and mean corpuscular volume (MCV) 1
• Prepare packed red blood cells: use group O, CMV-safe, freshly irradiated, Hemoglobin S-negative units that are antigen-negative for any maternal antibody 2
• Concentrate red blood cells to remove additives and increase hematocrit, minimizing fetal volume fluctuations 2
• Attach IV connection tubing to the blood unit, then attach a stopcock maintaining sterility 1
• Fill 20 mL syringes with blood, removing all air bubbles by holding syringes upright and tapping 1
• Prepare medications: vecuronium (0.1 mg/kg) or atracurium (0.4 mg/kg) for fetal paralysis, and 2% lidocaine in 3 mL syringe with 22- or 25-gauge needle for maternal local anesthesia 1

Maternal Preparation

• Intravenous access and prophylactic antibiotics are optional and at operator preference 1
• Perform hand hygiene 1
• Prepare the patient under aseptic conditions with antibacterial solution and sterile draping, leaving the abdomen exposed 1
• Cover ultrasound transducer with sterile cover 1

Ultrasound-Guided Site Selection

Target Site Identification

• Perform ultrasound to select the optimal puncture site from the following options: placental cord insertion, free loop of umbilical cord, fetal umbilical cord insertion, or intrahepatic vein 1
• The intrahepatic vein or placental cord insertion are preferred as they reduce procedure-related risks 3
• Measure the distance from maternal abdomen to the umbilical vein puncture site to ensure correct needle length 1
• Document baseline fetal heart rate 1

Needle Insertion and Access Confirmation

Vascular Access Technique

• Administer local anesthesia to the mother at the puncture site 1
• Inject fetus with intramuscular paralytic agent (vecuronium or atracurium) if necessary to minimize fetal movement 1
• Use a 20- or 22-gauge needle to enter the umbilical vein under continuous ultrasound guidance 1, 4
• Remove the stylet after needle placement 1

Confirming Intravascular Position

• If blood flow is immediate, obtain a 1 mL sample in a syringe and send to laboratory 1
• If flow is not immediate and Wharton's jelly is suspected, slowly and carefully reposition the needle to enter the vein 1
• Some operators document flow by injecting saline; if this is done prior to obtaining fetal blood sample, discard the first 1 mL of fetal blood as it may be diluted with saline 1
• Confirm fetal blood sample by comparing maternal (previously drawn and analyzed) and fetal hematocrit and MCV 1
• This confirmation may not be necessary if sampling a free loop or intrahepatic vein, or if flow is documented with saline 1

Blood Transfusion Procedure

Transfusion Execution

• Calculate the specific volume of blood needed to transfuse at the start of the procedure (this was ranked as the highest priority intraoperative step) 4
• Attach tubing to transfuse slowly; the assistant pushes blood slowly while watching the umbilical cord segment to confirm blood is flowing through the umbilical vein 1
• A small slow transfusion of blood may be performed prior to obtaining confirmatory laboratory results to prevent clot formation 1
• When fetal hematocrit returns and transfusion is confirmed necessary, proceed with calculated blood volume 1

Intra-Procedure Monitoring

• Intermittently obtain fetal heart rate throughout the procedure 1
• If transfusing a large amount of blood, consider obtaining a mid-procedure hematocrit 1
• Maintain needle stability to prevent lacerations and dislodging 5

Completion and Final Sampling

• When transfusion is complete, obtain final hematocrit and draw any other blood needed for work-up 1
• Some practitioners perform a Kleihauer-Betke test to determine the percentage of fetal and adult red blood cells in the final hematocrit 1

Optional Adjunctive Procedure

Intraperitoneal Transfusion

• Some operators choose to also perform an intraperitoneal transfusion, which allows slow absorption of blood over 7-10 days and may prolong the interval until the next transfusion 1
• Calculate intraperitoneal blood volume using the formula: (Gestational age in weeks - 20) × 10 = volume in mL (e.g., at 30 weeks: 30 - 20 = 10, therefore 100 mL blood) 1

Post-Procedure Management

Immediate Post-Transfusion Care

• After needle removal, watch the puncture site for streaming (bleeding) and check fetal heart rate for bradycardia 1
• Consider monitoring the patient and fetus for 1 hour after transfusion 1
• Once the gestational-age threshold for viability is reached, continuous fetal heart-rate monitoring is the highest priority postoperative step 4

Critical Competency Considerations

Operator Experience Requirements

• An experienced fetal interventionist should perform IUT procedures 4, 3
• Operators should perform a median of 20 IUT procedures during training to attain competency 4
• A median of 10 IUT procedures annually is required to maintain competency 4
• In centers where IUT is performed infrequently, referral to a more experienced center should be considered 4, 3
• Survival rates exceed 85% in specialized centers with multidisciplinary expertise, with overall survival around 90% in experienced hands 1, 3

Common Pitfalls and Caveats

Technical Challenges

• Avoid needle tip movement during syringe attachments and withdrawals by using appropriate connection systems 5
• Risk of neonatal cholestasis is highest when IUT requires transplacental needle passage 1
• Neurodevelopmental impairment risk is 4.8% overall but increases significantly with fetal hydrops and preterm birth <32 weeks 1
• There is marked variation in practice regarding blood preparation, preoperative medication, maternal anesthesia, cordocentesis site selection, use of fetal paralysis, and postoperative care 4

Documentation Requirements

• Label blood units intended for IUT clearly 2
• Differentiate transfusion documentation in the maternal medical record 2
• Prepare laboratory tubes for initial, midway, and final blood counts, plus additional tubes for genetic studies, liver function studies, or other tests as needed 1