What is the zygosity and chorionicity of dichorionic/diamniotic twins?

Dichorionic/diamniotic twins are classified as dizygotic twins, which means that they originate from two distinct eggs fertilized by two separate sperm. This type of twinning typically results in each twin having its own separate chorion and amnion, leading to the designation of "dichorionic" (which indicates two chorions) and "diamniotic" (which indicates two amnions).

The presence of two chorions and two amnions is an important characteristic that generally provides each twin with its own placental supply, reducing the likelihood of complications associated with shared placental structures, such as twin-to-twin transfusion syndrome.

In contrast, when twins share a chorion or amnion, they may be classified differently, such as monozygotic twins with a single chorion or amnion. However, in this scenario, the specific identification of dichorionic/diamniotic implies distinct individuality in both chorionic and amniotic layers, affirming the accurate classification of these twins as dizygotic with separate membranes.