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Twin-to-twin transfusion syndrome

Terms in this set (14)

placenta: -developing fetus receives nutrition (through umbilical cord)
-Where umbilical cord meets placenta it branches into many vessels (radiate out and penetrate placenta like roots of tree)
Twin placenta: more than one fetus in uterus must share resources provided by mother
-two main types of twin placentas: 1.dichorionic (each fetus connected to own separate placenta- although there might be competition between fetuses there is no direct sharing of blood bet. twins)
2.monochorionic (two fetuses share one placenta, monochorionic twins always identical twins (usually separated by thin wall (membrane) but have many direct connections to placenta), connections btw. blood vessels that radiate from each cord insertion are called vascular anastomoses (shunts)- allow passage of blood btw. their circulations, anastomoses found in all monochorionic pregnancies, twins exchange blood back and forth (in uncomplicated monochorionic pregnancies equal exchange in both directions -> balance btw. circulations)
-complicated monochorionic twins:

-sharing bet. monochorionic twins is not equal or unbalanced-> can lead to complications (TTTS is such a complication)

-type of placenta nurturing identical twins plays significant role in development of complications in multiple gestation
-the impetus for and the timing of the embryo to split into identical twins is unknown (the later this occurs the more complications are seen)
-type of placenta determined by when (in days) embryo randomly splits into twins following the fertilization of the egg (conception)
(Twinning within first 4 days ->dichorionic placentas-> these twins have lowest complication rates)
(Twinning four or more days after conception -> monochorionic (MC)placenta
btw. 4-8 days the MC twins will have separate sacs of water (diamnionic) despite a shared placenta, but after 8 days will also be in same sac (monoamnionic)
-Diamnionic monochorionic (4-8 days split) twins are most common placental type for identical twins (most cases of TTTS occur in this group)
-if twins have a MC placenta it is absolut proof that they are "identical"
-MC placenta contains two anatomic variables thought to develop randomly (contribute to and explain why, when and to what degree TTTS will affect twins)
-1. is the presence of blood vessels in placenta (connect the umbilical cords and circulations of the twins)
-2. is the variations in the way the twins share their common placenta
(in some MC twins both these abnormalities may be present)
-may threaten both twins
-unequal exchange of blood, placental sharing of nutrients,fluid, and oxygen
-donor twin sends blood and fluid to placenta but does not get equal amount back from placenta
-recipient twin also sends blood into placenta but gets back an excess of fluid and blood cells
-this met difference leaves donor short of fluid and placental supplies while recipient is overloaded
-occurs mainly b/c of blood vessel connections deep in placenta or on its surface
-artery of one twin may connect with artery of other twin (arterio-arterial anastomosis)
-similarly a vein of one twin can connect with corresponding vein from from the other (veno-venous anastomosis)
-these connections are on surface of placenta and permit blood exchange in both directions
-sometimes arteries coming from one twin to supply an area in placenta (the cotyledon) do not drain into a vein returning to same twin - blood is drained by a vein connections the other twin (such an arteriovenous anastomosis deep in placenta allow blood flow un one direction -> acts like one-way valve)
-if amount of blood flow in one direction can't be balanced by enough blood flow in opposite direction, then an imbalance is set up - if this imbalance progresses further it can lead to TTTS

-is a disease of placenta (or afterbirth)-affects identical twin pregnancies
-affects identical twins who share common monochorionic placenta
-shared placenta contains abnormal blood vessels (connect umbilical cords and circulations of the twins)
-common placenta may also be shared unequally by the twins (one twin may have a share too small to provide necessary nutrients to grow normally or even survive)
-events in pregnancy that lead to TTTS(timing of twinning event, number/type of connections vessels, and the way the placenta is shared by twins ) are all random events that have no primary prevention and are not hereditary or genetic
-can occur at any time during pregnancy (even while mother is in labor at term)
-placental abnormalities determine when and to what degree a transfusion occurs btw. the twin

-condition in which identical twins share blood supply due to an anomaly with the blood vessel connections of the placenta (b/c of connection smaller twin acts as donor for larger recipient twin-receives excess fluid resulting in an enlarged bladder ans an in area in amniotic fluid)
- TTTS phenomenon almost exclusive to monochorionic pregnancies
-natural history of severe TTTS well established with mortality rates approaching 80%-100% if left untreated (especially when it presents prior to 20 weeks gestation -> tends to be more severe and more rapidly progressive
Quintero et al. proposed staging system for TTTS (considers a sequence of progressive sonographic features
polyhydramnios in the recipient, severe oligohydramnios in donor but urine visible within the bladder of the donor
polyhydramnios in the recipient, a stuck donor, urine not visible within the donor's bladder
polyhydramnios and oligohydramnios, as well as critically abnormal Dopplers (at least one of absent or reverse end diastolic flow in the umbilical artery, reverse flow in the ductus venosus or pulsatile umbilical venous flow), with or without urine visualized within the donor's bladder
Stage 4:
presence of ascites or frank hydrops (fluid collection in two or more cavities) in either donor or recipient
Stage 5:
demise of either fetus. This staging system is descriptive but had not been validated as prognostically important
Source used by
Quintero RA, Morales WJ, Allen MH et al. Staging of twin-twin transfusion syndrome. J Perinatol 1999;19: 550-5.
-large study showed that Quintero stage at presentation, at first treatment and at worst stage did predict both prenatal and double survival but not survival of any twin
Tan TYT, Taylor MJO, Lee LY et al. Doppler for artery-artery anastomosis and stage-independentsurvival in twin-twin transfusion. Obstet Gyneco12004; 103: 1174-80.
-Duncombe et. al. also showed correlation of Quintero stage at initial presentation and perinatal survival

Duncombe GJ, Dickinson JE, Evans SF. Perinatal characteristics and outcomes of pregnancies complicated by twin-twin transfusion syndrome. Obstet Gynecol 2003; 101: 1190-6.
- Quintero staging system provides useful shorthand to describe progression of TTTA along a spectrum of severity
-Yet it has potential limitations in its use in guiding therapy