Ans. D. Intertwining. (Ref. Williams Obstetrics 22nd ed. ch. 39. Multifetal Gestation; Fig. 39-16).TypeUNIQUE COMPLICATIONSMONOAMNIONIC TWINSApproximately 1 percent of monozygotic twins are monoamnionic.A high fetal death rate is associated with this rare variety of monozygotic twinning.Intertwining of their umbilical cords, a common cause of death, is estimated to complicate at least half of cases.DISCORDANT TWINSThe cause of birthweight inequality in twin fetuses is often unclear, but evidence indicates that etiology in monochorionic twins differs from that in dichorionic twins.ACARDIAC TWINTwin reversed-arterial-perfusion (TRAP) sequence is a rare (1 in 35,000 births) but serious complication of monochorionic, monozygotic multiple gestation.CONJOINED TWINSThe majority are of the thoracopagus.Twin-to-Twin Transfusion SyndromeIn this syndrome, blood is transfused from a donor twin to its recipient sibling such that the donor becomes anemic and its growth may be restricted, whereas the recipient becomes polycythemic and may develop circulatory overload manifest as hydrops. The donor twin is pale, and its recipient sibling is plethoric. Seen in Monochorionic twin. Overview of the incidence of twin pregnancy Zygosity & corresponding twin-specific complicationsTwin-Specific Complication (percent)Type of TwinningTwinsFetal Growth RestrictionPreterm DeliveryPlacental Vascular AnastomosisPerinatal MortalityDizygotic802540010-12Monozygotic204050 15-18Diamnionic/dichorionic6-73040018-20Diamnionic/monochorionic13-14506010030-40Monoamnionic/monochorionic< 14060-7080-9058-60Conjoined0.002- 0.008--70-8010070-90Extra Educational points:In women with a uterus that appears large for gestational age, the following possibilities are considered:# Multiple fetuses# Elevation of the uterus by a distended bladder# Inaccurate menstrual history# Hydramnios# Hydatidiform mole# Uterine myomas# A closely attached adnexal mass# Fetal macrosomia (late in pregnancy)