Vandeplassche M, Podliachouk L, Beaud R
Can J Comp Med. 1970 Jul;34(3):218-26.
A study has been made of 44 cases of twin pregnancy in mares. The fetuses, foals, fetal membranes and blood groups of parents and foals were examined in order to determine the incidence of chorio-vascular anastomosis, blood chimaerism and freemartinism. All of the twins proved to be dizygotic and 33 of the 34 pregnancies were bicornual. Fusion of the chorion was seen in 14 of 22 placentas and macroscopic choriovascular bridges were observed in five of these, although blood chimaerism was diagnosed in 11 of 25 cases (44 per cent) examined. This would indicate a high incidence of microchoriovascular anastomosis. The fetal female genital organs of four heterosexual twins were found to be anatomically and histologically normal at autopsy despite the existence of blood chimaerism. Five other sexvalley mature mares born as heterosexual twins with chimaerism all had normal genital organs and estrus cycles and one of these has since become pregnant. The important interspecies differences with respect to the incidence and degree of choriovascular anastomosis and freemartinism are stressed and suggestions for a plausible explanation were advanced.
对44例母马双胎妊娠进行了研究。检查了胎儿、幼驹、胎膜以及亲本和幼驹的血型，以确定绒毛膜血管吻合、血液嵌合体和自由马丁现象的发生率。所有双胞胎均为异卵双生，34例妊娠中有33例为双角子宫妊娠。在22个胎盘中，有14个可见绒毛膜融合，其中5个观察到宏观的绒毛膜血管桥，尽管在25例检查病例中有11例（44%）被诊断为血液嵌合体。这表明微绒毛膜血管吻合的发生率很高。尽管存在血液嵌合体，但在尸检时发现4例异性双胞胎的胎儿雌性生殖器官在解剖学和组织学上正常。另外5匹作为异性双胞胎出生且具有嵌合体的性成熟母马，其生殖器官和发情周期均正常，其中1匹后来怀孕了。强调了在绒毛膜血管吻合和自由马丁现象的发生率及程度方面重要的种间差异，并提出了合理的解释建议。
