**Question:** The presence of multifetal gestation and subsequent disappearance of one or more fetuses called

A. Monochorionic diamniotic (MCDA) twin pregnancy
B. Monochorionic triamniotic (MCTA) twin pregnancy
C. Monochorionic monoamniotic (MCMA) twin pregnancy
D. Dichorionic diamniotic (DCDA) twin pregnancy

**Correct Answer:** **Dichorionic diamniotic (DCDA) twin pregnancy**

**Core Concept:** Multifetal gestation refers to the presence of more than one fetus in a single pregnancy. The chorion is a layer of trophoblast cells that forms the amnion, amniotic sac, and the amniotic fluid. Chorionicity refers to the number of layers of chorion (chorionae) present in a twin pregnancy. Amniotony refers to the number of amniotic sacs.

**Why the Correct Answer is Right:** In dichorionic diamniotic (DCDA) twin pregnancy, there are two layers of chorion and two amniotic sacs. This type of twin pregnancy is the most common, accounting for about 60-70% of twin pregnancies. DCDA twins develop from two separate fertilized eggs, resulting in two separate placentas and amniotic sacs for each fetus.

**Why Each Wrong Option is Incorrect:**

A. **Monochorionic diamniotic (MDDA) twin pregnancy** refers to a twin pregnancy with one layer of chorion and two amniotic sacs. In MDDA twin pregnancies, the two fetuses share a single placenta, leading to a higher risk of complications such as twin-to-twin transfusion syndrome and increased risk of prematurity.

B. **Monochorionic triamniotic (MCTA) twin pregnancy** refers to a twin pregnancy with one layer of chorion and three amniotic sacs. MCTA is extremely rare and usually results from the fusion of two or more fertilized eggs.

C. **Monochorionic monoamniotic (MMA) twin pregnancy** refers to a twin pregnancy with one layer of chorion and only one amniotic sac shared by both fetuses. MMA pregnancies are associated with significant complications, including cord entanglement and premature rupture of membranes.

**Clinical Pearl:** Understanding the classification of twin pregnancies is essential for anticipating and managing potential complications. In DCDA twins, having two placentas and amniotic sacs allows for better fetal monitoring and management of complications in comparison to MDDA and MMA twins.