Association of early cleavage, morula compaction and blastocysts ploidy of IVF embryos cultured in a time-lapse system and biopsied for genetic test for aneuploidy

Abstract

IVF embryos have historically been evaluated by morphological characteristics. The time-lapse system (TLS) has become a promising tool, providing an uninterrupted evaluation of morphological and dynamic parameters of embryo development. Furthermore, TLS sheds light on unknown phenomena such as direct cleavage and incomplete morula compaction. We retrospectively analyzed the morphology (Gardner Score) and morphokinetics (KIDScore) of 835 blastocysts grown in a TLS incubator (Embryoscope+), which were biopsied for preimplantation genetic testing for aneuploidy (PGT-A). Only the embryos that reached the blastocyst stage were included in this study and time-lapse videos were retrospectively reanalysed. According to the pattern of initial cleavages and morula compaction, the embryos were classified as: normal (NC) or abnormal (AC) cleavage, and fully (FCM) or partially compacted (PCM) morulae. No difference was found in early cleavage types or morula compaction patterns between female age groups (< 38, 38-40 and > 40 yo). Most of NC embryos resulted in FCM (≅ 60%), while no embryos with AC resulted in FCM. Aneuploidy rate of AC-PCM group did not differ from that of NC-FCM group in women < 38 yo, but aneuploidy was significantly higher in AC-PCM compared to NC-FCM of women > 40 yo. However, the quality of embryos was lower in AC-PCM blastocysts in women of all age ranges. Morphological and morphokinetic scores declined with increasing age, in the NC-PCM and AC-PCM groups, compared to the NC-FCM. Similar aneuploidy rates among NC-FCM and AC-PCM groups support the hypothesis that PCM in anomalous-cleaved embryos can represent a potential correction mechanism, even though lower morphological/morphokinetic scores are seen on AC-PCM. Therefore, both morphological and morphokinetic assessment should consider these embryonic development phenomena.

Figure 1

Percentage of embryos according to subgroups of initial zygote cleavage and morula compaction (NC-FCM, NC-PCM, AC-PCM, and AC-PCM), and stratified by female age. Qui-square test. p = 0.500. NC-FCM normal cleavage and fully compacted morula, AC-FCM abnormal cleavage and fully compacted morula, NC-PCM normal cleavage and partially compacted morula, AC-PCM abnormal cleavage and partially compacted morula.

Figure 2

Aneuploidy rates of embryos classified according to subgroups of initial zygote cleavage and morula compaction (NC-FCM, NC-PCM, and AC-PCM), and stratified into female age groups. NC-FCM normal cleavage and fully compacted morula, NC-PCM normal cleavage and partially compacted morula, AC-PCM abnormal cleavage and partially compacted morula. Qui-square test: *p < 0.001; **p < 0.001; ***p = 0.017.

Figure 3

(A) Morphological evaluation represented by the top-quality blastocyst rates. (B) Morphokinetics evaluation represented by the means of KIDScore and 95% confidence interval. Results were presented according to subgroups of initial zygote cleavage and morula compaction (NC-FCM, NC-PCM, and AC-PCM), and stratified into female age groups. NC-FCM normal cleavage and fully compacted morula, NC-PCM normal cleavage and partially compacted morula, AC-PCM abnormal cleavage and partially compacted morula.