The placenta of twins may be
A. Dichorionic and monoamniotic in dizygotic (DZ) twinsB. Dichorionic and monoamniotic in monozygotic (MZ) twins
C. Monochorionic and monoamniotic in DZ twins
D. Dichorionic and diamniotic in MZ twins
The answer is D
Dizygotic twins of
different sexes always have a dichorionic and diamniotic placenta, and
monochorionic monozygotic twins are always of the same sex. The dichorionic
placentas of dizygotic twins may be totally separated or intimately fused. Of
monozygotic twins, 20 to 30% have dichorionic placentation, the result of
separation of the blastocyst in the first 2 days after fertilization. The
majority of monozygotic twins have a diamniotic and monochorionic placenta. The
least common type of placentation in monozygotic twins is the monochorionic and
monoamniotic placenta; its incidence is only about 1%.
