Twin pregnancy, monochorionic/diamniotic, second trimester

This code identifies a twin gestation where the fetuses share a single chorion but have separate amniotic sacs, specifically during the second trimester of pregnancy. This monochorionic/diamniotic (MCDA) twin type carries specific risks due to the shared placenta, such as twin-to-twin transfusion syndrome (TTTS).

Apply this code when documentation clearly indicates a monochorionic/diamniotic twin pregnancy and the patient is in her second trimester (typically weeks 14 through 27+6 days). This diagnosis is typically established via ultrasound findings confirming the chorionicity and amnionicity.

• Always confirm both the chorionicity/amnionicity and the specific trimester from the physician's documentation.
• Do not confuse with dichorionic/diamniotic or monochorionic/monoamniotic twin pregnancies, which have different code assignments.
• This code should be sequenced as the primary diagnosis when the twin pregnancy itself is the focus of the encounter, or as a secondary diagnosis when other conditions are being managed in the context of this pregnancy.