Identification of the indicators for rescue ICSI: the efficacy oftime-lapse imaging for the signs of fertilization inivf

Abstract

We previously reported how the presence of the fertilization cone (FC) and cytoplasmic wave (CW) can act as indicators for the necessity of early-rescue ICSI after short-term insemination (ESHRE 2018). However, FC is present for only short durations. In addition, in some eggs it is difficult to identify CW due to cytoplasmic texture. Consequently, such determinations, when based upon one observational time point under an inverted microscope, can sometimes be difficult. Thus, we investigated whether a time-lapse incubator (TL) that allows the observation of embryos over time could be useful for identifying FC and CW. We analyzed 6,704 mature eggs from 2,212 cycles of 1,438 individuals that were collected and then subjected to IVF between 2014 and 2017. We performed insemination at 12:00, removed cumulus cells 5 hour after insemination, and then checked for the presence of the second polar body (2PB), FC, and CW under an inverted microscope. We repeated the observation when FC or CW was not identified, even in the presence of 1PB and 2PB. In a conventional-method group, we performed the second and subsequent observations for fertilization signs every 1-hour under an inverted microscope. Meanwhile, in the TL group, we performed observations for fertilization signs every 1-hour using time-lapse imaging. In both groups, we considered the observation of 2PB extrusion, or the observation of either FC or CW, to be a sign of fertilization. When no fertilization sign was identified by 19:00, we conducted rescue ICSI. We then compared the proportions of positive FC and CW identification, as well as differences in the accuracy of determination between the conventional-method and TL groups. A 2PB was observed in 2963 oocytes in the conventional-method group and 2548 oocytes in the TL group. The proportions of positive fertilization signs by FC were 13.0% and 19.9% in the conventional-method and TL groups, respectively, indicating that the proportion was significantly higher in the TL group. Meanwhile, those by CW were 70.1% and 62.2% in the conventional-method and TL groups, respectively, indicating that the proportion was lower in the TL group. The infertility rates of the embryos determined to have FC and CW were 3.1% and 1.0%, respectively, in the conventional-method group, and 0.2% and 0.1%, respectively, in the TL group; thus, the rate of infertility was significantly reduced in the TL group. Observation over time improves the accuracy of diagnosis for FC and CW, which makes time-lapse observation very useful for determining fertilization signs.