Twin pregnancy, monochorionic/monoamniotic, first trimester

This code identifies a twin gestation where both fetuses share a single chorion and a single amniotic sac, occurring specifically within the first trimester of pregnancy. This rare and high-risk type of twin pregnancy is associated with significant complications due to potential cord entanglement and other shared resource issues.

Apply this code when documentation clearly indicates a monochorionic/monoamniotic twin pregnancy confirmed by ultrasound in the first trimester. This diagnosis is typically established early in gestation based on the absence of an intervening membrane between the fetuses and a single placental mass.

• Always confirm the chorionicity and amnionicity through ultrasound reports.
• Ensure the documentation explicitly states "first trimester" for accurate period of gestation assignment.
• Do not confuse with monochorionic/diamniotic twin pregnancies (O30.02-) or dichorionic/diamniotic twin pregnancies (O30.00-).