Effect of sperm maturity and assisted oocyte activation on morphokinetics of early human embryos

Abstract

ICSI with testicular sperm extraction (TESE) is a feasible therapeutic option for azoospermic patients, however, testicular sperm has lower fertilizability owing to its immaturity. Assisted oocyte activation (AOA) is often used to treat activation failure after ICSI. The objective of this study was to assess the effect of sperm immaturity and induced oocyte activation on early embryonic events by Time-lapse monitoring (TM). Comparative morphological assessment of ICSI zygotes. A total of 74 patients comprised of 3 groups, 57 with ejaculated sperm (EJ), 10 with AOA, and 7 with TESE. Number of zygotes in each group was 196, 48, and 65, respectively. For AOA, oocytes were briefly exposed to Ca ionophore after ICSI. Inseminated oocytes were individually cultured in a TM system (EmbryoscopeTM). Images were acquired every 10 min for up to 144 hrs. Zygotes were categorized as either those which developed to blastocysts (BL), or those which did not (non-BL). Time points of each morphokinetic event, such as 2nd polar body extrusion (PBII), pronuclear (PN) appearance/disappearance, embryonic cell divisions, and intervals between cell cleavages were analyzed. Blastulation rates for EJ, AOA, and TESE were 54.1, 41.7, and 44.6%, respectively, and all comparable. After transferring 59 EJ embryos 13 (22.0%) implanted (IMP). In EJ, the time point for the 2-cell stage was shorter in BL than in non-BL (P < 0.01), while the interval between the 2- and 3-cell stage was longer in BL (P < 0.01). Among replaced embryos, IMP zygotes developed to the 8-cell stage faster than their non-IMP (55.0 ± 6 vs. 61.1 ± 8 hrs, P < 0.01). In both AOA and TESE, time points for PN disappearance, the 2-, and 4-cell stage were shorter in BL than in non-BL (P < 0.05), while intervals between the 2- and 3-cell stage in AOA, and between the 4- and 5-cell stage in TESE were longer in BL than in non-BL (P < 0.05). Overall, in comparison to EJ zygotes, TESE extruded PBII more slowly (P < 0.05), while AOA developed faster to the 4-cell stage (P < 0.05). Faster and more synchronous cleavage was associated with higher developmental potential of zygotes irrespective of sperm origin and activation methods. Although the blastocyst formation rate was similar, sperm immaturity appeared responsible for slower first cleavage, and chemically induced activation accelerated early cleavage.