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| Monchorionic Diamniotic Twin Placenta |
| Etiology • Unknown |
| Pathogenesis • Separation of blastomeres • To result in diamniotic monochorionic placentation twinning occurs between 3 and 8 days from fertilization • At this point no amnion has developed so that two sacs will form, |
| Epidemiology • Monozygotic twinning is relatively steady in all populations at 3.5/1000. • With assisted fertilization techniques the relative proportion of monozygotic twinning is declining |
| General Gross Description • Usually fused placental disks showing chorionic surface with insertion of two umbilical cords • Separation of two halves of placenta by thin delicate dividing membrane which can not be pulled apart • Superficial anastamoses may be evident between two circulations |
| General Microscopic Description • Examination of the dividing membrane shows amniotic epithelium and mesoderm apposed mesoderm of a second amnion • No intervening chorion seen • Cannot determine which villi perfused which twin • Cannot detect deep anastamoses without special studies • All cases presumed to have vascular anastamoses |
| Clinical Correlation • Complications of twinning include premature delivery, possibility of twin-twin transfusion, and increased morbidity and mortality |
| References • Benirschke K, Kaufmann P. Pathology of the human placenta, 3rd ed. New York: Springer-Verlag, 1995, pp. 719-733. |
| Monchorionic Diamniotic Twin Placenta |
| Synopsis by: Melinda Sanders M.D. (T88100M29040)[54] |
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