Question 1

What is ICD-10 code O43.021?

Accepted Answer

O43.021 is the ICD-10-CM diagnosis code for fetus-to-fetus placental transfusion syndrome, first trimester. An abnormal transfer of blood occurs between twins or multiples through a shared placenta during the first trimester of pregnancy. O43.021 sits in the ICD-10-CM chapter for pregnancy, childbirth and the puerperium (o00-o9a), within the section covering maternal care related to the fetus and amniotic cavity and possible delivery problems (o30-o48).

O43.021 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.

Confirm multiple gestation is documented before assigning this code.

Question 2

Is O43.021 an HCC code?

Accepted Answer

No. O43.021 is a billable ICD-10-CM code but does not map to any payment HCC category under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can still be reported on Medicare Advantage encounter data submissions, but it does not contribute to the beneficiary's Risk Adjustment Factor (RAF) score and therefore does not affect the risk-adjusted capitation payment to the plan. V28 reached 100% phase-in for payment year 2026.

Question 3

Is O43.021 billable?

Accepted Answer

Yes. O43.021 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. O43.021 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Question 4

Which HCC does O43.021 map to under V28?

Accepted Answer

O43.021 does not map to a CMS-HCC V28 payment category. Check the current CMS-HCC V28 model file for payment year 2026 rather than an older V24 tip sheet.

Question 5

What does O43.021 pay in RAF?

Accepted Answer

O43.021 has no separately stated V28 community RAF weight. If it is not a V28 payment HCC, it adds nothing to a community RAF score.

Question 6

What is the V28 vs V24 difference for O43.021?

Accepted Answer

O43.021 does not map to a payment HCC under either the CMS-HCC V28 risk adjustment model or the older V24 model. V28 reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition. Because neither community model rewards O43.021 with a risk adjustment factor, it contributes zero to a Medicare Advantage beneficiary's V28/V24 community RAF score in either version. Coders should check whether provider documentation supports a more specific child code that does map to a community payment HCC.

Question 7

What documentation supports O43.021?

Accepted Answer

Confirm multiple gestation is documented before assigning this code This condition is specific to monochorionic placentas shared by multiple fetuses O43.021 is not a CMS-HCC payment code, so MEAT is not the payment hook. Documentation still has to support the diagnosis if you report it.

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O43.021

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O43.021 ICD-10-CM Code: Fetus-to-fetus placental transfusion syndrome, first trimester

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O43.021

Is O43.021 an HCC code?

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