Twin pregnancy, monochorionic/monoamniotic, third trimester

This code signifies a twin gestation where both fetuses share a single chorion and a single amniotic sac, and the pregnancy has progressed to the third trimester (28 weeks gestation or greater). This is a high-risk pregnancy due to potential complications like twin-to-twin transfusion syndrome (TTTS) and cord entanglement.

Apply this code when documentation explicitly states a monochorionic/monoamniotic twin pregnancy in the third trimester. This diagnosis is typically established through ultrasound findings confirming the absence of an intervening membrane between the fetuses and a single placental mass.

• Always confirm the chorionicity and amnionicity from the medical record, usually from ultrasound reports.
• Ensure the gestational age is documented as 28 weeks or greater to accurately assign the third-trimester code.
• Do not confuse with monochorionic/diamniotic twin pregnancies (O30.02-) or dichorionic/diamniotic twin pregnancies (O30.00-).