<prompt> Which of the following is not a criterion for antenatal diagnosis of Twin-Twin transfusion syndrome?Oligohydramnios in donor fetusDichorionicityHemoglobin difference of 5 gdL between the two foetusesWeight difference of 20 between the two foetuses  <response>: Ans. b Dichorionicity Ref. Dutta Obst 6th1209; Williams 22nd Table 39-3; p. 929UNBALANCED INTERTWIN TRANSFUSION - unbalanced intertwin transfusion through vascular anastomoses between the two circulations of monochorionic twins ACUTE Twin-embolization syndrome CHRONIC Twin-twin transfusion syndrome REVERSE Acardiac twinning- Monochorionic twins have a significantly greater risk of abortion than dichorionic twins the vanishing Twin.- Acardiac twin or Twin reversed-arterial-perfusion TRAP sequence is a rare 1 in 35,000 births but serious complication of monochorionic, monozygotic multiple gestation.- Monozygotic twins 33: same sex identical genotype1 Perinatal mortality 2.5 times greater than for dizygotic twins2 Fetal anomalies 3-7 times higher than in dizygotic twins singletons often only affecting one twin: anencephaly, hydrocephalus, holoprosencephaly, cloacal exstrophy, VATER syndrome, sirenomelia, sacrococcygeal teratomaDichorionic Diamniotic Twins 30 separation at two-cell stage blastomere approximately 60 hours 4 days after fertilization 2 separate fusedunfused placentas membrane 2 mm due to 2 separate chorionic sacs 2 separate amniotic sacs 92 accurate for dichorionic diamniotic twins sign triangular projection of placental tissue insinuated between layers of intertwin membraneMonochorionic Diamniotic Twins 69-80 separation in blastocyst stage between 4th and 7th day after fertilization chorion already developed and separated from embryo 2 separate amniotic sacs in single chorionic sac Common monochorionic placenta has vascular communications in 100Cx:1 Twin-twin transfusion syndrome2 Twin embolization syndrome DIC in surviving twin from transfer of thromboplastin; 17 morbidity mortality of survivor after fetal death of twin3 Acardiac parabiotic twinMonochorionic Monoamniotic Twins 1 division of embryonic disk between 8th and 12th day after fertilization amniotic cavity already developed common amniotic chorionic sac, no separating membraneDays after FertilizationEmbryologic EventCleavage Chorionresults in Amnion1-2Cell divisions - moruladidi3-4Chorionic differentiation 6Blastocyst implants in endometriummonodi8Amnionic differentiationmonomono13Division of embryonic diskmonomono Entanglement of cords the only definitive positive sonographic sign of monoamnionicityCx: double perinatal mortality up to 451 Entangled umbilical cord 702 True knot of cord3 Conjoined twins umbilical cord with 3 vessels, shared fetal organs, continuous fetal skin contourPrognosis: 40 survival rateDizygotic Twins 23 FRATERNAL TWINS fertilization of two ova by two separate spermatozoa during two simultaneous ovulations occurring either in both ovaries or in one ovary superfetation fertilization of two ova by two separate spermatozoa during two subsequent ovulations frequency unknown superfecundation two ova fertilized by two different fathers very rare Incidence: 1:80 to 1:90 births Predisposing factors:- Advanced maternal age increased up to age 35: reduced gonadal-hypothalamic feedback with increase of FSH levels- Ovulation-inducing agents multiple pregnancies in 6-17 with clomiphene, in 18-53 with Pergonal- Maternal history of twinning 3 times as frequent compared with normal population- Increased parity- Maternal obesity- Race with inherited predisposition for multiple ovulations Blacks Whites Asians different phenotypes; same opposite sex always dichorionic diamnioticOverview of the incidence of twin pregnancy Zygosity corresponding twin-specific complicationsTwin-Specific Complication percentType 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--70-8010070-90TWIN-TO-TWIN TRANSFUSION SYNDROME In 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 manifesting as hydrops. The donor twin is pale, and its recipient sibling is plethoric. Similarly, one portion of the placenta often appears pale compared with the rest of the placenta. Complications: The neonatal period may be complicated by circulatory overload with:- Heart failure- Occlusive thrombosis.- Polycythemia may lead to severe hyperbilirubinemia and kemicterus. 