Walker Susan P, Meagher Simon, White Susan M
Perinatal Medicine, Mercy Hospital for Women, 163 Studley Road, Heidelberg 3084, Australia.
Prenat Diagn. 2007 Apr;27(4):369-72. doi: 10.1002/pd.1670.
To present the risk factors, prenatal and postnatal implications of monochorionic dyzygotic twinning.
We present a case of monochorionic twins diagnosed on first-trimester ultrasound following a 2-embryo transfer in vitro fertilisation pregnancy. Postnatal buccal smears performed as part of a twin research study revealed the twins to be dizygous, and DNA testing on peripheral blood lymphocytes confirmed the presence of blood chimerism.
Despite the monochorionic placentation, buccal swabs revealed discordant results for all four microsatellite loci tested, consistent with dizygosity. Zygosity testing on peripheral blood lymphocytes revealed that, of the nine DNA microsatellite loci tested, three had all four parental alleles represented. This result was concordant between the twins. The diagnosis of blood chimerism was thus confirmed, presumably due to the inter-twin vascular anastomoses of the monochorionic placenta.
Monochorionic dizygous twinning is rare, but appears to be more common after assisted reproduction. It is presumed that outer cell mass fusion may occur when two embryos are replaced in close proximity. These pregnancies are not only at risk for the usual complications of monochorionicity, but also have the potential to be heterokaryotypic. Postnatally, the twins may have long-term blood chimerism.
阐述单绒毛膜双羊膜囊双胎妊娠的危险因素、产前及产后影响。
我们报告一例在体外受精妊娠进行双胚胎移植后，孕早期超声诊断为单绒毛膜双胎的病例。作为双胎研究的一部分进行的产后颊黏膜涂片显示这对双胞胎为双卵双胎，对外周血淋巴细胞进行的DNA检测证实存在血液嵌合体。
尽管是单绒毛膜胎盘，但颊黏膜拭子显示所检测的所有四个微卫星位点结果不一致，符合双卵双胎特征。对外周血淋巴细胞进行的合子型检测显示，在所检测的九个DNA微卫星位点中，有三个位点呈现所有四个亲本等位基因。双胞胎之间的这一结果是一致的。由此证实了血液嵌合体的诊断，推测是由于单绒毛膜胎盘的双胎间血管吻合所致。
单绒毛膜双卵双胎妊娠较为罕见，但在辅助生殖后似乎更为常见。据推测，当两个胚胎紧邻植入时可能会发生滋养外胚层融合。这些妊娠不仅有单绒毛膜性常见并发症的风险，而且有可能是异核型的。产后，双胞胎可能会有长期的血液嵌合体现象。
