The frequency of collapse as a predictor of feline blastocyst quality

Morphokinetic changes and apoptotic cell death in vitrified and non-vitrified in vitro-produced ovine embryos

This article addresses morphokinetic changes and the extent of apoptosis in vitrified and non-vitrified in vitro-derived ovine blastocysts. Cumulus-oocyte complexes were collected after ovarian scarification obtain after slaughter and in vitro maturation was performed in TCM 199 medium supplemented with Earle's Salt, 10 % of FBS, and 5 µg/mL of LH/FSH at 38 °C for 24 h. After maturation, the oocytes were co-incubated with thawed ram semen (IVF) for 19 h.Embryo development was monitored with the aid of the Primo Vision Time-Lapse (TL) system. Twenty-five out of thirty-one ovine blastocysts that were vitrified using the Cryotop system at the early blastulation stage of development subsequently re-expanded. Both the vitrified (n = 25) and non-vitrified (control group: n = 28) blastocysts were examined for detection of apoptosis (TUNEL assay) and total blastomere counts at the time they attained the expanded blastocyst stage. Blastocyst formation occurred earlier in non-vitrified than in vitrified ovine embryos (147:49 ± 20:23 compared with 156:46 ± 19:24; hours:minutes post-insemination; mean ± SD; P < 0.05). The average number of blastocyst collapses was greater (2.45 ± 1.64 compared with 1.45 ± 1.64), but the number of weak contractions was less for vitrified than non-vitrified ovine blastocysts (P < 0.05). The mean number of blastomeres was greater (131.8 ± 38.6 compared with 91.5 ± 18.3; P < 0.05) while the number of TUNEL-positive cells (4.4 ± 1.6 compared with 6.3 ± 2.3) and apoptotic index (3.4 ± 1.2 % compared with 6.9 ± 2.6 %) were less (P < 0.05) in non-vitrified compared with vitrified blastocysts. Vitrification of ovine embryos was associated with a delayed blastocyst formation, greater numbers of apoptotic cells, significant reduction in the number of blastomeres, and higher/lower incidence of blastocyst collapse/weak contractions.

Relationships of morphological and phototextural attributes of presumptive ovine zygotes and early embryos to their developmental competence in vitro: a preliminary assessment using time-lapse imaging

The assessment of morphology and digital image opacity may provide valuable information on the present embryo quality. Time-lapse imaging has been employed in research to establish a means of monitoring the dynamic nature of preimplantation embryo development. The aim of present study was to use time-lapse imaging for assessing various prospective morphometric and phototextural markers of the developmental potential of in vitro-derived ovine embryos. Oocytes were obtained by scarification of ovaries from nine Polish Longwool ewes. After in vitro maturation (IVM) and fertilization (IVF) of oocytes with fresh ram semen, the development of embryos to the blastocyst stage was monitored and evaluated using Primo Vision time-lapse imaging technology. Commercially available Image-Pro^® Plus software was used to measure zona pellucida thickness, embryo diameter, total area of the perivitelline space, cellular grey-scale pixel intensity and cellular pixel heterogeneity. Statistical assessment of all attributes was done at various time points during embryo development (i.e., presumptive zygote stage: t(0); first cleavage detected at t(2) or t(3); and second cleavage detected at t(4) or t(6)). Out of thirty-seven zygotes analyzed in this study, five did not divide, 26 arrested before and six developed to the blastocyst stage. Our present results indicate that most parameters analyzed did not differ among embryos varying in their developmental fate except for the perivitelline space area that was greater (P<0.05) for non-dividing zygotes than future blastocysts at the presumptive zygote stage (4040±1850 vs. 857±262 µm², respectively; means±SEM). Consequently, the measurement of perivitelline space at t(0) can potentially be used to prognosticate developmental potential of in vitro-produced ovine embryos albeit further confirmational studies are needed.

A comparison of in vitro culture systems for cat embryos

The aim of this study was to compare several culture systems for cat embryos. Domestic cat oocytes were matured in vitro (IVM), fertilized (IVF), and cultured individually or in groups in drops under oil (20 μL or 50 μL) and in 16 microwell dishes (Primo Vision®). Moreover, the effects of co-culture with a) uncleaved oocytes, b) homospecific and c) heterospecific co-culture with cat and sheep companion embryos were investigated using a time-lapse system. A higher proportion of blastocysts and hatching blastocysts was observed after culture in Primo Vision® dishes compared with the classical individual (p < 0.001) and group (p < 0.05) culture systems. Culture of presumptive zygotes 16 hpi and the presence of uncleaved oocytes did not reduce blastocyst development compared with culture of embryos 24 hpi without uncleaved oocytes. Co-culture with later-stage companion cator sheep embryos accelerated development of catembryos. The highest percentage of blastocysts was obtained in the group co-cultured with sheep embryos (54%). Moreover, the blastocyst cavity formed on average 10 h faster in this group than for the control group and for embryos co-cultured with cat embryos. The proportion of hatching blastocysts was similar in the co-cultures with cat and with sheep embryos (20% vs. 22%) and significantly (p < 0.05) than in the control group (12%).

Focus on time-lapse analysis: blastocyst collapse and morphometric assessment as new features of embryo viability

The main goal of assisted reproductive technology (ART) is to achieve a healthy singleton live birth after the transfer of one embryo. A major objective of IVF scientists has always been to use adequate criteria for selecting the embryo for transfer according to its implantation potential. Indeed, embryo quality is usually assessed by evaluating visual morphology, which relies on the removal of the embryo from the incubator and might include inter- and intra-evaluator variation among embryologists. Recently, an advancement in embryo culture has taken place with the introduction of a new type of incubator with an integrated time-lapse monitoring system, which enables embryologists to analyse the dynamic events of embryo development from fertilization to blastocyst formation. This novel practice is rapidly growing and has been used in many IVF centres worldwide. Therefore, the main aim of this review is to present the benefits of time-lapse monitoring in a modern embryology laboratory; in particular, we discuss blastocyst collapse and morphometric blastocyst assessment, and analyse their association with embryo viability and implantation potential. In addition, we highlight preliminary studies involving artificial intelligence and machine learning models as non-invasive markers of clinical pregnancy.

Timing of cleavage divisions determined with time-lapse imaging is linked to blastocyst formation rates and quality of in vitro-produced ovine embryos

Time-lapse (TL) imaging provides a practical and safe tool to constantly monitor the development of in vitro-derived embryos. TL may help develop novel methods of predicting the timing of embryo cleavage that will lead to optimizing blastocyst cryopreservation or transfer. The primary objective of the present study was to employ TL imaging to examine associations among the division kinetics of ovine embryos, their quality and rates of development to the blastocyst stage. Oocytes were collected by ovary scarification from 78 Longwool ewes slaughtered in the breeding season (November-March). Cumulus oocyte complexes (COCs) were matured for 24 h in TCM 199 media containing 0.1 IU/mL LH/FSH and 10% FBS. In-vitro fertilization was carried out by co-incubation of semen and COCs for 19 h. Presumptive zygotes were placed in microwells, in droplets of Cult medium (Gynemed, Lensahn, Germany). Digital images of developing embryos were captured every 10 min by Primo Vision TL system (EVO+; Vitrolife, Göteburg, Sweden). The following time intervals were recorded: from IVF to the attainment of two-cell (t2), three-cells (t3) or four-cell (t4) stage, to morula detection (tM), blastulation (tSB) and blastocyst formation (tB). Lastly, the duration of the second cell cycle (cc2; t3-t2) and complete synchronous cell division (s2; t4-t3) were calculated, and the incidence of developmental anomalies noted. Out of 147 embryos selected for TL observations, 55 (37.4%) developed to the blastocyst stage (normally developing embryos, NE) and 92 (62.6%) failed to reach the blastocyst stage (arrested embryos, AE; P < 0.05). Mean t2, tM, s2 and cc2 were all less (P ≤ 0.02) in NE compared with AE. Approximately 61.9% of embryos exhibited developmental anomalies (35.5% in the NE group and 78.2% in the AE group; P < 0.05) and AE exceeded (P < 0.05) NE in the proportion of FRG (blastomeric fragmentation), IRR (blastomeres of irregular size after cleavage), DC (direct cleavage) and MA (multi-morphological aberrations). Of all NE, 63.6% were classified as good quality and 36.4% as poor quality blastocysts (P < 0.05). Good quality ovine blastocysts attained t2, t3, t4, tSB and tB stages earlier (P ≤ 0.03) than poor quality blastocysts and none of the poor quality blastocysts was seen to hatch. To recapitulate, the present results indicate that the kinetics of early ovine embryo development are significant predictors of their potential to develop to the blastocyst stage and the markers of blastocyst quality. Time-lapse imaging may serve as a useful technique for predicting the outcome and enhancing efficacy of in vitro embryo production in sheep.