Twins Flashcards
Discus monozygotic twins
Rarely familial, not mat age effect.
1/3: division at modular stage (dichorionic/diamniotic)
2/3: division at blastocyst stage (d4-7) of the inner cell mass (monochorionic/diamniotic).
Amnion forms at d9 so if division if after this (monochorionic/monoamniotic)
Discuss vanishing twin
One twin suffer early fetal death and isn’t aborted.
Areas of degenerate villi/amorphous debris in free membranes.
Occur in DC and MC. Cause unexplained AFP levels and chromosome results
Estimated false result caused by VT: 0.3-0.7%
When do zygosity testing
When need to establish if twins are monochorionic.
Requested in one twin has phenotype.
Look at polymorphic markers of multiple chromosomes. Need both parents and both twin samples.
Calculate Hayes for likelihood of same alleles being inherited by chance
Discuss TRAP
Twin Reversed Arterial Perfusion.
Rare and unique to MC placentas with artery-artery and vein-vein anastomoses.
1 twin is acardiac and is perfumed in a reverse direction by the pump twin.
Poorly oxygenated arterial blood passes to the acardiac twin and even more poorly oxygenated blood to the normal,pump, twin.
Normal twin: poor prognosis: 50%. (Usually cardiac overload/ preterm birth)
Discuss TTTP
Twin to Twin Transfusion Syndrome.
Placental vascular anastomoses connecting the vein of one foetus to the artery of the other foetus allowing unidirectional blood flow from donor to recipient.
15% MC/DA.
Discordant fetal growth:
Donor: smaller with oligohydromnios and anaemia.
Recipient: larger with Polyhydromnios and enlarged bladder.
What’s the TTTP treatment
Serial amnio reductions (increases risk of preterm birth)
Fetoscopic laser ablation of placenta (find interconnecting blood vessels and laser beam them to coagulate)
What’s the mortality rate of twins
6 fold increase of mortality in twins to singletons.
Preterm delivery. IUGR. Congenital anomalies (anacephaly, CHD)
Discuss dizygotic twins
Incidence increases with maternal age.
Can be familial.
Genetic basis is maternal in origin (incidence of multiple follicle growth and ovulation rate)
Genes: TGF9’signalling pathway
