| 词条 | Monochorionic twins |
| 释义 |
Amniocity and zygosityMonochorionic twins generally have two amniotic sacs (called Monochorionic-Diamniotic "MoDi"), but sometimes, in the case of monoamniotic twins (Monochorionic-Monoamniotic "MoMo"), they also share the same amniotic sac. Monoamniotic twins occur when the split takes place after the ninth day after fertilization.[2] Monoamniotic twins are always monozygotic (identical twins).[3] Monochorionic-Diamniotic twins are almost always monozygotic, with a few exceptions where the blastocysts have fused.[2] DiagnosisBy performing an obstetric ultrasound at a gestational age of 10–14 weeks, monochorionic-diamniotic twins are discerned from dichorionic twins. The presence of a "T-sign" at the inter-twin membrane-placental junction is indicative of monochorionic-diamniotic twins (that is, the junction between the inter-twin membrane and the external rim forms a right angle), whereas dichorionic twins present with a "lambda (λ) sign" (that is, the chorion forms a wedge-shaped protrusion into the inter-twin space, creating a rather curved junction).[4] The "lambda sign" is also called the "twin peak sign". At ultrasound at a gestational age of 16–20 weeks, the "lambda sign" is indicative of dichorionicity but its absence does not exclude it.[5] In contrast, the placentas may be overlapping for dichorionic twins, making it hard to distinguish them, making it difficult to discern mono- or dichorionic twins on solely the appearance of the placentas on ultrasound. ComplicationsIn addition to a shared placenta, monochorionic twins also have their circulatory systems intermingled in random and unpredictable circulatory anastomoses. This can cause disproportionate blood supply, resulting in twin-to-twin transfusion syndrome (TTTS) in 20%[1] of MoDi pregnancies. This is the main complication of monochorionic twins. The 80% of MoDi pregnancies without TTTS still have high rates of birth weight discordance, fetal growth restriction, prematurity and resultant cesarean section deliveries.[1] One twin may also fail to develop a proper heart and become dependent on the pumping activity of the other twin's heart, resulting in twin reversed arterial perfusion.[2] If one twin dies in utero, blood accumulates in that twin's body, causing exsanguination of the remaining twin.[2] In the case of monoamniotic twins the risk of complications is substantially higher because of additional potential umbilical cord entanglement and compression.[3] However, the perinatal mortality of monochorionic twins is fairly low.[1] See also
References1. ^1 2 3 {{cite journal |vauthors=Cordero L, Franco A, Joy SD, O'shaughnessy RW |title=Monochorionic diamniotic infants without twin-to-twin transfusion syndrome |journal=J Perinatol |volume=25 |issue=12 |pages=753–8 |date=December 2005 |pmid=16281049 |doi=10.1038/sj.jp.7211405 |url=}} {{Twin conditions}}{{Pathology of pregnancy, childbirth and the puerperium}}2. ^1 2 3 4 5 {{cite book |author=Shulman, Lee S.; Vugt, John M. G. van |title=Prenatal medicine |publisher=Taylor & Francis |location=Washington, DC |year=2006 |pages=Page 447 |isbn=0-8247-2844-0 |oclc= |doi= |accessdate=}} 3. ^1 Pregnancy-Info -- > Monoamniotic Twins Retrieved on July 9, 2009 4. ^{{Cite journal | last1 = Sepulveda | first1 = W. | last2 = Sebire | first2 = N. J. | last3 = Hughes | first3 = K. | last4 = Odibo | first4 = A. | last5 = Nicolaides | first5 = K. H. | title = The lambda sign at 10-14 weeks of gestation as a predictor of chorionicity in twin pregnancies | doi = 10.1046/j.1469-0705.1996.07060421.x | journal = Ultrasound in Obstetrics and Gynecology | volume = 7 | issue = 6 | pages = 421–423 | year = 1996 | pmid = 8807758 | pmc = }} 5. ^{{Cite journal | last1 = Sepulveda | first1 = W. | last2 = Sebire | first2 = N. | last3 = Hughes | first3 = K. | last4 = Kalogeropoulos | first4 = A. | last5 = Nicolaides | first5 = K. | title = Evolution of the lambda or twin-chorionic peak sign in dichorionic twin pregnancies | doi = 10.1016/S0029-7844(97)85858-9 | journal = Obstetrics & Gynecology | volume = 89 | issue = 3 | pages = 439–441 | year = 1997 | pmid = 9052601 | pmc = }} 3 : Twin|Reproduction in mammals|Zoology |
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