Exchange Transfusion in Pregnant Females with Congenital Methemoglobinemia
Exchange red cell transfusion is the preferred intervention for pregnant women with congenital methemoglobinemia requiring acute treatment, as it avoids the significant teratogenic risks of methylene blue while effectively correcting maternal hypoxia and protecting the fetus. 1, 2
When Exchange Transfusion is Indicated
Exchange transfusion should be performed when:
- Symptomatic methemoglobinemia develops during pregnancy requiring intervention beyond supplemental oxygen 1, 2
- Methemoglobin levels are significantly elevated with clinical signs of hypoxia (neurologic symptoms, cardiac symptoms, or severe cyanosis) 1
- The patient requires treatment but methylene blue is contraindicated or refused due to teratogenic concerns 1, 2
- Major surgery is planned during pregnancy where prolonged anesthesia or exposure to triggering drugs is inevitable 1
Pre-Procedure Preparation
Blood product preparation:
- Obtain appropriate matched blood with hematocrit of 75% that is compatible with maternal blood 3
- Ensure blood bank has adequate supply available, particularly in centers where products are not readily available 1
- Prepare fresh frozen plasma if needed 1
Multidisciplinary coordination:
- The decision must involve hematology, obstetrics, and blood bank services 1, 2
- Discuss risks and benefits with the patient, weighing fetal hypoxia risks against procedural risks 1
Exchange Transfusion Procedure
Technical approach:
- Perform under ultrasound guidance to identify optimal vascular access 3
- Select puncture site along the umbilical vein based on fetal and placental position: placental insertion, fetal insertion, or fetal intraabdominal segment 3
- Confirm fetal origin of blood obtained and estimate hemoglobin level immediately 3
- Continue exchange until target hemoglobin of 16 g/dL is reached 3
- The procedure achieves rapid correction of anemia while eliminating incompatible or dysfunctional red blood cells 3
Monitoring during procedure:
- Use co-oximetry to identify methemoglobin levels throughout 1, 2
- Provide supplemental oxygen to maintain adequate tissue oxygenation 1, 2
- Monitor for signs of hypoxia including neurologic and cardiac symptoms 1
Post-Procedure Management
Immediate follow-up:
- Monitor methemoglobin levels and hemoglobin after exchange 2
- Assess fetal well-being with appropriate obstetric monitoring 1
- Repeat exchange transfusion may be needed monthly to maintain adequate hemoglobin levels in severe cases 3
Ongoing pregnancy management:
- Continue supplemental oxygen as needed 2
- Avoid precipitating factors including local anesthetics (benzocaine, prilocaine, lidocaine), dapsone, sulfonamides, and nitrates 1
- Plan for scheduled delivery to ensure availability of hematology support and blood bank resources 2
Critical Pitfalls to Avoid
Do not use methylene blue prophylactically or as first-line therapy in pregnancy:
- Methylene blue causes teratogenic effects including jejunal/ileal atresia, fetal demise, hemolytic anemia, hyperbilirubinemia, and skin photosensitization 1
- Methylene blue should only be used when risks of maternal hypoxia outweigh teratogenic risks, typically in life-threatening situations 1, 2
- If methylene blue must be used emergently, systemic maternal administration is theorized to be lowest risk to the fetus 4
Do not delay exchange transfusion:
- Exchange transfusion should not be delayed if time permits and matched blood is available 1
- Therapeutic whole blood exchange has an 81.6% survival rate in refractory cases 2
- Fetal hypoxia from maternal methemoglobinemia causes intrauterine growth restriction, prematurity, morphological and functional cardiac changes, and potentially fetal demise 1, 2
Alternative Adjunctive Therapies
If exchange transfusion is not immediately available: