Observation of human embryonic behavior in vitro by high-resolution time-lapse cinematography
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Observation of human embryonic behavior in vitro by high-resolution time-lapse cinematography Kyoko Iwata1 • Yasuyuki Mio1
Received: 2 July 2015 / Accepted: 16 December 2015 Ó Japan Society for Reproductive Medicine 2015
Abstract Assisted reproductive technology (ART) has yielded vast amounts of information and knowledge on human embryonic development in vitro; however, still images provide limited data on dynamic changes in the developing embryos. Using our high-resolution time-lapse cinematography (hR-TLC) system, we were able to describe normal human embryonic development continuously from the fertilization process to the hatched blastocyst stage in detail. Our hR-TLC observation also showed the embryonic abnormality of a third polar body (PB)-like substance likely containing a small pronucleus being extruded and resulting in single-pronucleus (1PN) formation, while our molecular biological investigations suggested the possibility that some 1PN embryos could be diploid, carrying both maternal and paternal genomes. Furthermore, in some embryos the extruded third PB-like substance was eventually re-absorbed into the ooplasm resulting in the formation of an uneven-sized, two-PN zygote. In addition, other hR-TLC observations showed that cytokinetic failure was correlated with equal-sized, multi-nucleated blastomeres that were also observed in the embryo showing early initiation of compaction. Assessment combining our hR-TLC with molecular biological techniques enables a better understanding of embryonic development and potential improvements in ART outcomes.
& Kyoko Iwata [email protected] 1
Mio Fertility Clinic, Reproductive Centre, 2-1-1 Kuzumo-minami, Yonago, Tottori, Japan
Keywords Compaction Cytokinetic failure Highresolution time-lapse cinematography (hR-TLC) Multinucleated blastomere (MNB) Uneven-sized pronuclei
Introduction Assisted reproductive technology (ART) allows us to observe and monitor human embryonic development in vitro and to evaluate embryo quality before transfer, with several ART-based assessments of the developmental potential of human embryos previously reported [1–4]. The most common method of assessment during ART is morphology-based analysis of specific embryonic characteristics, which can be scored at various stages (pronuclear, cleavage, and blastocyst) [5, 6]. However, this quality control approach needs improvement with implantation rates of good quality embryos limited to 30–40 % per embryo transfer (ET) [7]. Indeed, based on the standard morphological assessment, ET with early cleavage-stage embryos has a better chance of achieving pregnancy than ET with blastocysts [8, 9]. On the other hand, embryos at the blastocyst stage are less likely to be aneuploid, and reported implantation rates are higher when blastocysts have been transferred [10]. Therefore, many facilities offering ART extend in vitro culture of embryos up to the blastocyst stage and then transfer blastocysts on day 5 after oocyte retrieval. However, these prolonged cultures can cause advers
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