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Twin Anemia-Polycythemia Sequence: Understanding TAPS

Assigned clinical reviewerMichael Yuzefovich· MD, FACOGDraft · pending clinical reviewUpdated

What does the evidence say about twin anemia-polycythemia sequence?

  1. Small placental vascular connections can allow a gradual imbalance in red blood cells. The donor twin may develop anemia and the recipient polycythemia. The consequences differ for each twin, so the team evaluates both babies rather than focusing only on the smaller one. 1
  2. SMFM describes middle cerebral artery Doppler measurements and the difference between twins as part of prenatal assessment for TAPS. These results require specialist interpretation using the relevant thresholds, gestational age, and other findings. 2
  3. TTTS commonly involves an imbalance in amniotic fluid, whereas TAPS can have a different presentation. The conditions should not be assumed interchangeable. A fetal team may need to evaluate for more than one complication in a shared-placenta pregnancy. 3
  4. TAPS can arise spontaneously or after laser surgery for TTTS. The stage, gestational age, and condition of each twin influence whether the next step is close surveillance, a fetal intervention, or delivery. Evidence does not support one identical plan for every case. 4
  5. Doppler assesses blood-flow patterns without drawing blood from the fetus. A measurement is part of a broader surveillance assessment and may need follow-up. Ask which vessel was assessed and what a change would mean for the plan. 5

When should TAPS monitoring be discussed?

  • First trimester. Early in pregnancy, document whether the twins share a placenta.
  • Second trimester. During monochorionic surveillance, ask how Doppler assessment for TAPS fits the plan.
  • Third trimester. Before birth, clarify any blood-count assessment and follow-up the neonatal team may need for each baby.

Questions to discuss with your care team

Decision pointWhat to clarify
FindingWhich Doppler results support concern for TAPS?
SeverityHow are both babies affected and what would change the current plan?
After birthWhat neonatal assessments and longer-term follow-up are needed?

Frequently asked questions

Can TAPS occur when the amniotic fluid looks normal?

Yes. Unlike the typical fluid imbalance of TTTS, TAPS may develop with relatively normal fluid around the twins. This is one reason the clinician considers Doppler and other findings alongside fluid measurements.

Would I feel that one twin is anemic?

Pregnant people rarely have a specific symptom of TAPS. The condition is assessed through fetal surveillance rather than maternal sensations. Keep the scheduled scans and report new symptoms or movement concerns to your care team.

What is the role of middle cerebral artery Doppler?

The speed of blood flow in this brain artery helps the specialist assess anemia and polycythemia patterns. The values for both twins and their difference are interpreted together; a single number copied from a report is insufficient.

Can TAPS happen after TTTS laser surgery?

Yes. Follow-up after a TTTS procedure includes watching for TAPS and other complications. A successful earlier procedure does not mean that all later shared-placenta surveillance can stop.

Does TAPS mean both babies have low red blood cells?

No. The donor twin has anemia, while the recipient has an increased red-cell concentration. These create different circulation concerns and may require different care before or after birth.

When is a specialized fetal-center consultation needed?

SMFM recommends consultation for more advanced TAPS before 32 weeks or when other complications raise concern. Your clinician should explain the urgency and referral pathway based on the complete findings.

What options might the fetal team discuss?

Depending on the case, options can include close monitoring, blood-related fetal procedures, laser surgery, or a delivery plan. Each has potential benefits and risks. Ask which problem the proposed step addresses for each baby.

Will the babies need follow-up after birth?

Yes. The neonatal team assesses blood counts, circulation, and other needs, especially if the babies arrive early. Ask how appointments will track growth and development after discharge, even when the immediate course is reassuring.

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References

  1. Twin-Anemia Polycythemia Sequence

    ISUOG · https://www.isuog.org/clinical-resources/patient-information-series/patient-information-pregnancy-conditions/multiple-pregnancies/twin-anemia-polycythemia-sequence.html

  2. Society for Maternal-Fetal Medicine Consult Series #72: Twin-twin transfusion syndrome and twin anemia-polycythemia sequence

    SMFM · https://publications.smfm.org/publications/574-society-for-maternal-fetal-medicine-consult-series-72/

  3. Twin-twin transfusion syndrome (TTTS)

    ISUOG · https://www.isuog.org/clinical-resources/patient-information-series/patient-information-pregnancy-conditions/multiple-pregnancies/twin-twin-transfusion-syndrome-ttts.html

  4. ISUOG Practice Guidelines (updated): role of ultrasound in twin pregnancy

    PubMed Central · https://pmc.ncbi.nlm.nih.gov/articles/PMC11788470/

  5. Doppler assessment in twin pregnancies

    ISUOG · https://www.isuog.org/clinical-resources/patient-information-series/patient-information-pregnancy-conditions/multiple-pregnancies/doppler-assessment-in-twin-pregnancies.html

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