Revealing the secret life of pre-implantation embryos by time-lapse monitoring: A review

A comparison of the morphokinetic profiles of embryos developed from vitrified versus fresh oocytes

RESEARCH QUESTION

Do morphokinetic profiles and treatment outcomes differ between embryos developed from vitrified or fresh oocytes?

DESIGN

Retrospective multicentre analysis using data from eight CARE Fertility clinics across the UK between 2012 and 2019. Patients receiving treatment using embryos developed from vitrified oocytes (n = 118 women, n = 748 oocytes), providing 557 zygotes during this time period, were recruited and matched with patients undergoing treatment with embryos developed from fresh oocytes (n = 123 women, n = 1110 oocytes), providing 539 zygotes in the same time frame. Time-lapse microscopy was used to assess morphokinetic profiles, including early cleavage divisions (2- through to 8-cell), post-cleavage stages including time to start of compaction, time to morula, time to start of blastulation and time to full blastocyst. Duration of key stages such as the compaction stage were also calculated. Treatment outcomes were compared between the two groups (live birth rate, clinical pregnancy rate and implantation rate).

RESULTS

A significant delay of 2-3 h across all early cleavage divisions (2- through to 8-cell) and time to start of compaction occurred in the vitrified group versus fresh controls (all P ≤ 0.01). The compaction stage was significantly shorter in vitrified oocytes (19.02 ± 0.5 h) compared with fresh controls (22.45 ± 0.6 h, P < 0.001). There was no difference in the time that fresh and vitrified embryos reached the blastocyst stage (108.03 ± 0.7 versus 107.78 ± 0.6 h). There was no significant difference in treatment outcomes between the two groups.

CONCLUSION

Vitrification is a useful technique for extending female fertility with no effects on IVF treatment outcome.

Impact of sperm characteristics on time-lapse embryo morphokinetic parameters and clinical outcome of conventional in vitro fertilization

BACKGROUND

Sperm abnormalities may negatively affect embryo development.

OBJECTIVES

To determine the influence of sperm abnormalities (morphology, motility, DNA fragmentation) on embryo morphokinetic variables and clinical outcome of conventional IVF.

MATERIALS AND METHODS

Participants were 86 couples undergoing in vitro fertilization (IVF). Sperm morphology was evaluated according to the strict criteria proposed by Kruger/Tygerberg. CASA system was applied for sperm motility assessment. Sperm DNA fragmentation was assessed by the chromatin structure assay (SCSA). Morphokinetic parameters were determined in 223 embryos obtained from conventional IVF only and cultured in a single-step medium using time-lapse imaging technology.

RESULTS

Time-lapse variables from the initial embryo development, such as time of pronuclei fading (tPNf) and time for two cells (t2), were those more strongly related with abnormalities of sperm motility, morphology, and DNA fragmentation. Sperm morphological abnormalities rather than sperm motility were more closely associated with embryo morphokinetics. Sperm head defects were mainly correlated with the last stages of embryonic development (t9 to tHB), sperm midpiece defects with intermediate cleaving embryos (t5-t9), and sperm tail defects with the initial stages of embryonic development (tPNa-t4). Excess residual cytoplasm was positively correlated with all embryo morphokinetic parameters except t2 and tM. Absence of acrosomes, pinheads, coiled tails, and multiple sperm morphological defects correlated negatively with time-lapse embryo morphokinetic variables.

DISCUSSION

A large number of sperm-related variables, including frequency of specific morphological defects, morphological indexes, DNA fragmentation and motility, and time-lapse embryo variables, such as time intervals based mainly of 15 time points were recorded.

CONCLUSION

There were strong associations between specific sperm defects of the head, midpiece, and tail with certain stages of embryonic development from observation of pronuclei to the hatched blastocyst. Coiled tail, cumulative head defects, and multiple abnormalities index (MAI) were associated both with embryo morphokinetics and the implantation success.

Correlations between embryo morphokinetic development and maternal age: Results from an intracytoplasmic sperm injection program

Objective

It is widely accepted that aging decreases women’s fertility capacity. The aim of this study was to assess correlations between maternal age and the morphokinetic parameters and cleavage pattern of embryos.

Methods

The morphokinetics of embryos derived from women <30, 30–35, 36–40, and >40 years of age were compared retrospectively in terms of time of second polar body extrusion, time of pronuclei appearance, time of pronuclei fading, and time of two to eight discrete cells (t2–t8). Furthermore, abnormal cleavage patterns such as uneven blastomeres at the two-cell stage, cell fusion (Fu), and trichotomous mitoses (TM) were assessed.

Results

Only t5 occurred later in women aged 36–40 and >40 years when compared with those aged <30 and 30–35 years (p<0.001). Other morphokinetic timing parameters, as well the presence of uneven blastomeres, were comparable between the groups (p>0.05). However, Fu and TM were more common in women aged >40 years than in younger women (p<0.001).

Conclusion

Maternal age was correlated with the cleavage pattern of embryos. Therefore, evaluating embryo morphokinetics may contribute to optimal embryo selection, thereby increasing fertility in patients with advanced maternal age.

Does rescue in vitro maturation of germinal vesicle stage oocytes impair embryo morphokinetics development?

SummaryCurrently, rescue in vitro maturation (IVM) is not a routine method in assisted reproductive treatment (ART) programmes but is a promising procedure for ART to improve IVM. The aim of this study was to compare embryo morphokinetics of germinal vesicles (GV) with metaphase II (MII) oocytes from controlled ovarian hyperstimulation (COH) cycles by time-lapse photography monitoring (TLM). Morphokinetics of the same number of embryos derived from the in vivo (group I) and rescue of in vitro matured oocytes (group II) from 310 patients were analyzed and compared retrospectively. The time to form second PB extrusion (tPB2), time of pronuclei appearance (tPNa), time of pronuclei fading (tPNf) and time of two to eight discrete cells (t2-t8) were assessed. Abnormal cleavage patterns such as uneven blastomeres at the two-cell stage, cell fusion (Fu), trichotomous mitoses (TM), and the rates of embryo arrest were assessed. These data showed that tPB2, tPNa, tPNf, t2, t3 and t4 stages took place later in group II compared with group I (P<0.001, P=0.017, P<0.001, P<0.001, P<0.001, P<0.001, respectively). The rates of uneven blastomeres, Fu, TM, and embryo arrest were increased significantly in group II compared with group I (P=0.001, P<0.001, P=0.003, P<0.001, respectively). Based on the exact annotation of timing parameters and cleavage patterns, the present data agreed with the concept that rescue IVM of oocytes negatively influences embryo morphokinetics. Therefore, cautious use of embryos derived from rescue IVM of GV oocytes should be made.

Lower blastocyst quality after conventional vs. Piezo ICSI in the horse reflects delayed sperm component remodeling and oocyte activation

PURPOSE

The aim of this study was to evaluate the differential effects of conventional and Piezo-driven ICSI on blastocyst development, and on sperm component remodeling and oocyte activation, in an equine model.

METHODS

In vitro-matured equine oocytes underwent conventional (Conv) or Piezo ICSI, the latter utilizing fluorocarbon ballast. Blastocyst development was compared between treatments to validate the model. Then, oocytes were fixed at 0, 6, or 18 h after injection, and stained for the sperm tail, acrosome, oocyte cortical granules, and chromatin. These parameters were compared between injection techniques and between sham-injected and sperm-injected oocytes among time periods.

RESULTS

Blastocyst rates were 39 and 40%. The nucleus number was lower, and the nuclear fragmentation rate was higher, in blastocysts produced by Conv. Cortical granule loss started at 0H after both sperm and sham injection. The acrosome was present at 0H in both ICSI treatments, and persisted to 18H in significantly more Conv than Piezo oocytes (72 vs. 21%). Sperm head area was unchanged at 6H in Conv but significantly increased at this time in Piezo; correspondingly, at 6H significantly more Conv than Piezo oocytes remained at MII (80 vs. 9.5%). Sham injection did not induce significant meiotic resumption.

CONCLUSIONS

These data show that Piezo ICSI is associated with more rapid sperm component remodeling and oocyte meiotic resumption after sperm injection than is conventional ICSI, and with higher embryo quality at the blastocyst stage. This suggests that there is value in exploring the Piezo technique, utilized with a non-toxic fluorocarbon ballast, for use in clinical human ICSI.

Pronuclear pattern does not predict morphokinetics behavior in human embryos

The purpose was to investigate the correlation between pronuclei (PN) morphology and morphokinetic behaviors of derived embryos with time lapse monitoring (TLM) in assisted reproduction setting. Over time, PN morphology from PN appearance (PNA) to PN fading (PNF), PNF according to size, contact, number and position of nuclear precursor bodies (NPBs) within each PN and morphokinetics variables, including absolute time points, relative timing parameters, cleavage patterns and arrest rate, were evaluated using TLM. There were insignificant relationship between morphokinetics variables including tBP2, tPNA, tPNF, t2, t3, t4, t5, t6, t7, t8, S1, CC2, S2 and Z scoring according Z1 to Z4 (p > .05). Also, an insignificant relationship was noticed between uneven blastomeres, reverse cleavage embryos and Z scoring (p > .05). However, there were significant correlations between the rates of direct and arbitrary cleavage as well as arrested embryos and Z scores. Combined PN morphology and embryo kinetic evaluation were suggested in assisted reproduction programs.