Monochorionic monoamniotic twin pregnancy
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At the time the article was created Yuranga Weerakkody had no recorded disclosures.View Yuranga Weerakkody's current disclosures
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It accounts for the minority (~5%) of monozygotic twin pregnancies and ~1-2% of all twin pregnancies. The incidence is ~1 in 10000 of all pregnancies 2.
This type of pregnancy carries a relatively high incidence of congenital anomalies 4.
It results from a separation of a single ovum at ~ 8-13 days following formation (i.e. later than with an MCDA pregnancy). By this time a trophoblast has already formed, yielding a single placenta. These fetuses share a single chorionic sac, a single amniotic sac, and most often a single yolk sac. The twins are identical (and of course of the same gender).
- shows a twin pregnancy with a single gestational sac and a most often a single yolk sac (which helps to differentiate from a DCDA and MCDA pregnancy)
- there is no inter-twin membrane: theoretically, this differentiates from a DCDA and MCDA pregnancy
- however, even in an MCDA pregnancy, the intertwin membrane may be difficult to see
- therefore non-visualization of the intertwin membrane is not in itself diagnostic
Features noted on a second-trimester scan includes:
- specific to an MCMA pregnancy
- common to both MCMA and MCDA pregnancies
- a single placenta is seen
- absent twin peak sign
Treatment and prognosis
An MCMA pregnancy carries the highest level of potential complications out of all twin pregnancies (with reported rates of overall perinatal mortality up to 70-80% 1). These include:
- problems related to abnormal placental vascular anastomoses
- demise of one twin: often associated with some adverse outcome to the other twin
- placental insertion related problems
- umbilical cord related complications