Chromosomal mosaicism, the coexistence of cells with different chromosomal content, has been documented in human embryos for 3 decades. Early versions of preimplantation genetic testing for aneuploidy (PGT-A) did not measure mosaicism, either because typically only a single cell was assessed or because the technique could not accurately identify it. Although this led to a straightforward diagnosis (an embryo was considered either normal or abnormal), it simply avoided the issue and, in hindsight, may have led to numerous misdiagnoses with negative clinical consequences. Modern PGT-A evaluates a multicellular biopsy specimen with techniques capable of recognizing intermediate copy number signals for chromosomes or subchromosomal regions. We are, therefore, inevitably confronted with the issue of mosaicism and the challenge of managing embryos producing such results in the clinic. Here we discuss recent data showing that not only mosaicism in general, but specific features of mosaicism detected with PGT-A, are associated with variable clinical outcomes. The conclusion is evident: mosaicism should be considered for more informed and improved embryo selection in the clinic.

染色体镶嵌现象，即具有不同染色体含量的细胞共存，已在人类胚胎中记录了 3 年。早期版本的非整倍性植入前基因检测 (PGT-A) 没有测量嵌合体，要么是因为通常只评估单个细胞，要么是因为该技术无法准确识别它。尽管这导致了直接的诊断（胚胎被认为是正常或异常），但它只是避免了这个问题，事后看来，可能导致了许多误诊，并带来负面的临床后果。现代 PGT-A 使用能够识别染色体或亚染色体区域的中间拷贝数信号的技术评估多细胞活检标本。因此，我们是 不可避免地面临镶嵌问题和在临床上管理产生这种结果的胚胎的挑战。在这里，我们讨论了最近的数据，这些数据表明，不仅一般的镶嵌现象，而且用 PGT-A 检测到的镶嵌现象的特定特征都与可变的临床结果相关。结论是显而易见的：嵌合体应考虑在临床中进行更明智和改进的胚胎选择。