Plachot M, Junca A M, Mandelbaum J, Cohen J, Salat-Baroux J
U 173 INSERM Groupe de Recherches sur la Fécondation in vitro, Hôpital Necker-Enfants-Malades, Paris.
Reprod Nutr Dev (1980). 1988;28(6B):1781-90.
Abnormal embryo development represents the major cause of implantation failures and accounts for the low rate of human fertility in vivo or in vitro. Chromosome abnormalities are widely involved in this process as 26% of oocytes, 8% of fertilizing spermatozoa and 29% of preimplantation embryos carry a chromosome aberration induced by meiotic (aneuploidy) or mitotic (mosaic) non disjunctions. Fertilization anomalies (possibly increased by in vitro procedures) were recorded: 1.6% of embryos resulted from parthenogenesis and 6.4% were polyploid (mainly polyspermic). A morphological, histological and ultrastructural study of embryos recovered after in vivo or in vitro fertilization showed some anomalies: multinucleated blastomeres, cytoplasmic fragments in the perivitelline space, vacuoles, associated or not with developmental impairement. Finally, a few embryos appeared to be free of abnormalities. The analysis of in vitro developmental capacities of normal or abnormal embryos showed great differences: parthenones exceptionally reached the blastocyst stage and therefore probably did not implant. The diploid embryos used in this study were (for ethical reasons) more or less fragmented and gave evidence of low developmental capacities, limited to the 3rd cleavage. Triploid embryos were able to further develop as some of them reached the early blastocyst stage; they represented the major cause of chromosomal 1st trimester abortions. It is interesting to note that 47% of tripronucleated ova divided directly into 3 and 6 cells (probably via a tripolar spindle) instead of 2 and 4 cells as classically described. Finally, tetraploid embryos expressed a precocious lethality as none developed beyond the 3rd cleavage. To conclude, many embryos carry genetic and/or cytological abnormalities which may be enhanced by superovulation treatments. The selection proceeds through all pre- and postimplantation steps, and as a matter of fact nor more than 0.6% newborns are abnormal.
胚胎发育异常是植入失败的主要原因，也是体内或体外人类生育率低的原因。染色体异常广泛参与这一过程，因为26%的卵母细胞、8%的受精精子和29%的植入前胚胎携带由减数分裂（非整倍体）或有丝分裂（嵌合体）不分离引起的染色体畸变。记录到受精异常（可能因体外操作而增加）：1.6%的胚胎来自孤雌生殖，6.4%为多倍体（主要是多精受精）。对体内或体外受精后回收的胚胎进行的形态学、组织学和超微结构研究显示了一些异常：多核卵裂球、卵周间隙中的细胞质碎片、空泡，与发育受损有关或无关。最后，一些胚胎似乎没有异常。对正常或异常胚胎的体外发育能力分析显示出很大差异：孤雌胚胎极少能发育到囊胚阶段，因此可能无法植入。本研究中使用的二倍体胚胎（出于伦理原因）或多或少都有碎片化现象，并且显示出发育能力较低，仅限于第三次卵裂。三倍体胚胎能够进一步发育，因为其中一些达到了早期囊胚阶段；它们是孕早期染色体流产的主要原因。有趣的是，47%的三原核卵直接分裂为3个和6个细胞（可能通过三极纺锤体），而不是如经典描述的那样分裂为2个和4个细胞。最后，四倍体胚胎表现出早熟致死性，因为没有一个能发育到第三次卵裂以后。总之，许多胚胎携带遗传和/或细胞学异常，超排卵治疗可能会加剧这种异常。选择过程贯穿植入前和植入后的所有步骤，事实上，出生时异常的新生儿不超过0.6%。
