Clin: Multifetal Gestation and Malpresentation - Moulton Flashcards
two separate ova are fertilized by two separate sperm
- are distinct pregnancies coexisting in the same uterus
- each will have it’s own amnion, chorion and placenta
fraternal (dizygotic) twins
arise from the cleavage of a single fertilized ovum at various stages during embryogenesis
- arrangement of fetal membranes and placentas will depend on the time at which the embryo divides
identical (monozygotic) twins
how many chorions, how many amnions for dichorionic diamniotic monozygotic placentation?
2 placenta
2 amnions
- cleavage at days 0-3
- can be two separate placentas or one fused
- 30% on monozygotic twins have this presentation
how many chorion, how many amnions for monochorionic diamniotic monozygotic placentation?
1 placenta
2 amnions
- cleavage at days 4-8
69% of monozygotic twins have this presentation
how many chorion, how many amnion for monochorionic monoamniotic monozygotic placentation?
1 placenta
1 amnion
- cleavage days 9-12
- 1% on monozygotic twins have this placentation
- is the most dangerous since there are not separating amnions
- cord entanglement risk if high
- net mortality in these twins is 50-80%
what is a craniopagus?
twins joined at the cranium
- 2% incidence
what is a thoracopagus?
twins joined at the chest wall
- 30-40% incidence
what is an ischiopagus?
twins joined by the coccyx and sacrum
- 6% incidence
what is the frequency of monozygotic twins?
constant among all populations at 1 in 250 births
- 1/3 of spontaneous twins are monozygotic
what are the influences of dizygotic twins?
- maternal age: 2x more common after 35 y/o
- family hx and ethnicity: lower among asians, Western nigerian tribe has dizygotic twinning occurance of 1 in 22 gestations
- 2/3 of spontaneous twins are dizygotic
when would you suspect multiple gestations?
- hCG higher than normal
- uterus palpates larger than dates
- auscultation of more than 1 fetal HR
- pregnancy has occurred after ovulation induction or IVF
prognosis and expected morbidity of twins is strongly dependent on what?
zygosity
- is the most important step after diagnosing twins!
monozygotic twins have increased incidence of what?
- congenital anomalies
- weight discordancy
- twin-twin transfusion syndrome (TTTS)
- neorologic squeale
- premature delivery
- fetal demise
US to determine zygosity:
- different fetal gender
- visualization of a thick amnoin-chorion septum
- “peak” or “inverted V” sign at the base of the septum
dizygotic
US to determine zygosity
- dividing membrane is fairly thin
monozygotic
what if US is not definitive in determining zygosity?
- inspect placenta after delivery
- DNA analysis
- cleavage occurs 13-15 days
- 1 in 70,000 deliveries
- mortality rates 50%
- c-section delivery
- advancement of imaging allows mapping of shared organs and more successful surgical separation procedures
- elective termination if cardiac or cerebral fusion is identified
conjoined twins
- 90% occur in monochorionic twins
- most common type is arterial-arterial followed by arterial-venous and then venous-venous
- vascular communications between 2 fetuses through the placenta can cause problems (abortion, polyhydramnios, TTTS, fetal malformation)
interplacental vascular anastomoses
results secondary to uncompensated arterial-venous anastomoses in a monochorionic placenta
- leads to a net transfer of blood flow going from 1 twin to other
twin-twin transfusion syndrome (TTTS)
what are the fetal complications of TTTS?
- donor twin
- recipient twin
- donor twin: hypovolemia, hypotension, anemia, oligohydramnios, growth restriction
- recipient twin: hypervolemia, polyhydramnios, thrombosis, HTN, polycythemia, edema, cardiomegaly, CHF
what are both twins at risk for in TTTS?
heart failure -> demise
can you diagnose TTTS on US?
yes!
- donor twin: smaller, “stuck” appearance, oligohydramnios
- recipient twin: larger, polyhydramnios, ascites
what is the tx of TTTS?
- serial amniocentesis with amniotic fluid reduction (can reduce preterm contractions secondary to uterine distention)
- laser photocoagulation of the anastamotic vessels on the placenta (performed at specialized centers)
- arterial blood flow from the donor twin enters the arterial circulation of the recipient twin
- reversed blood flow may cause thrombosis within critical organs or atresias due to trophoblastic embolization
- the recipient twin, being perfused in reverse direction with poorly oxygenated blood fails to develop normally -> known as ACARDIAC twin (fully formed lower extremities, no amatomic structures cephalad of the abdomen)
abnormalities in monozygotic twins with arterial to arterial anastomoses