A monochorionic-monoamniotic (MCMA) twin pregnancy is a sub type of monozygotic twin pregnancy. 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.
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 yolk sac and a single amniotic sac. The twins are identical (and of course of the same gender).
This type of pregnancy carries a relatively high incidence of congenital anomalies 4.
- shows a twin pregnancy with a single gestational sac and a single yolk sac (differentiating from a DCDA and MCDA pregnancy).
- there is no inter twin membrane : theoretically this differentiates from a DCDA and MCDA pregnancy.
- however, even in a MCDA pregnancy the intertwin membrane may be difficult to see.
- therefore non-visualisation of the intertwin membrane is not in itself diagnostic.
Features noted on a 2nd trimester scan includes
- specific to a MCMA pregnancy
- common to both MDMA and MDCA pregnancies
- a single placenta is seen :
- absent twin peak sign
A 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
- twin to twin transfusion syndrome : this particular complication only occurs in ~ 10 - 15 % of MCMA pregnancies and therefore less common than MCDA pregnancies 7.
- twin embolisation syndrome :
- twin reversed arterial perfusion sequence :
- demise of one twin : often associated with adverse outcome for the other twin
- placental insertion related problems
- umbilical cord related complications
- 1. Baxi LV, Walsh CA. Monoamniotic twins in contemporary practice: a single-center study of perinatal outcomes. J. Matern. Fetal. Neonatal. Med. 2010;23 (6): 506-10. doi:10.3109/14767050903214590 - Pubmed citation
- 2. Wladimiroff JW, Eik-Nes S. Ultrasound in obstetrics and gynaecology. Elsevier Science Health Science div. (2009) ISBN:0444518290. Read it at Google Books - Find it at Amazon
- 3. Cordero L, Franco A, Joy SD. Monochorionic monoamniotic twins: neonatal outcome. J Perinatol. 2006;26 (3): 170-5. doi:10.1038/sj.jp.7211457 - Pubmed citation
- 4. Dørum A, Nesheim BI. Monochorionic monoamniotic twins--the most precarious of twin pregnancies. Acta Obstet Gynecol Scand. 1991;70 (4-5): 381-3. - Pubmed citation
- 5. Dias T, Mahsud-dornan S, Bhide A et-al. Cord entanglement and perinatal outcome in monoamniotic twin pregnancies. Ultrasound Obstet Gynecol. 2010;35 (2): 201-4. doi:10.1002/uog.7501 - Pubmed citation
- 6. Merz E, Bahlmann F. Ultrasound in obstetrics and gynecology. Thieme Medical Publishers. (2005) ISBN:1588901475. Read it at Google Books - Find it at Amazon
- 7. Entezami M, Albig M, Knoll U et-al. Ultrasound Diagnosis of Fetal Anomalies. Thieme. (2003) ISBN:1588902129. Read it at Google Books - Find it at Amazon
- 8. Levi CS, Lyons EA, Dashefsky SM et-al. Yolk sac number, size and morphologic features in monochorionic monoamniotic twin pregnancy. Can Assoc Radiol J. 1996;47 (2): 98-100. - Pubmed citation
- 9. Bromley B, Benacerraf B. Using the number of yolk sacs to determine amnionicity in early first trimester monochorionic twins. J Ultrasound Med. 1995;14 (6): 415-9. J Ultrasound Med (abstract) - Pubmed citation
- 10 .Hill LM, Chenevey P, Hecker J et-al. Sonographic determination of first trimester twin chorionicity and amnionicity. J Clin Ultrasound. 24 (6): 305-8. doi:10.1002/(SICI)1097-0096(199607/08)24:63.0.CO;2-M - Pubmed citation
- 11. Entezami M, Albig M, Knoll U et-al. Ultrasound Diagnosis of Fetal Anomalies. Thieme. (2003) ISBN:1588902129. Read it at Google Books - Find it at Amazon
Synonyms & Alternative Spellings
|Synonyms or Alternative Spelling||Include in Listings?|
|Monochorionic monoamniotic twins||✗|
|Monochorionic monoamniotic (MCMA) twins||✗|
|MCMA twin pregnancy||✗|
|Monochorionic monoamniotic twins (MMT)||✗|
|Monochorionic - monoamniotic twin pregnancy||✗|
|Monochorionic - monoamniotic twins||✗|
|Mono - Mono twins||✗|