The Cumulus Cells and Oocytes: A Systematic Review of Extended Culture for Intracytoplasmic Sperm Injection

Currently-placed protocols for extended culture for in vitro fertilization(IVF)and intracytoplasmic sperm injection(ICSI)are not uniformly standardized in determining the optimal stage of oocyte maturation for maximizing clinical outcomes.The objective of this systematic review is to elucidate the relationship between extended cumulus-oocyte culture and its effect on the clinical outcomes of IVF/ICSI.We included an electronic search on PubMed Central as well as the Journal of Fertility and Sterility to yield seven studies on extended oocyte culture for IVF/ICSI.Four of the seven investigations illustrate the promising beneficial relationship of extended culture with conditioned or supplemented media to mimic physiological uterine conditions.Three studies did not capture beneficial relationships between extended oocyte culture and clinical outcomes with unconditioned,unsupplemented maturation medium.Improvement in fertilization rates,oocyte development,and live birth rates may be achieved by extended culture with the addition of supplemental biochemicals.The usage of follicular fluid,cumulus cells,and meiotic inhibitors imitates the physiological in vivo conditions,whereas extended oocyte culture imitates in vivo temporal conditions.The conjunction of extended oocyte culture with supplemented metabolites,either added in maturation media manually or secreted by cumulus-oocyte complexes,mimics natural uterine physiological conditions to improve clinical outcomes for patients seeking IVF/ICSI.

Extended Culture of Early Stage Embryos in Frozen-thawed Cycles

Objective To investigate the impact of extended culture of early stage embryos on pregnancy outcome of frozen embryo transfer （FET）. Methods The survival rates of embryos after thawing and pregnancy outcome following FET were compared retrospectively between zygote and cleavage embryos which cultured to cleavage stage or extended cultured to blastocysts. Results A total of 425 zygote embryos in 67 cycles were thawed. After thawing, the survival rate was 94.4% and with an average transfer of 2.8 embryos, the clinical pregnancy rate was 55.2% （37/67）. In 222 FET cycles, totally 1 270 cleavage stage embryos were thawed and the overall survival rates were 80.3%. With an average transfer of 2.7 embryos, the clinical pregnancy rate was 55.4% （123/222）. A significantly lower percentage of degenerated embryos were found for zygotes （5.6%） than that for cleavage stage embryos （19.7%） （P〈0.01）. The clinical pregnancy rate was 53.4% （116/217） in the group of transfer at cleavage stage, while the clinical pregnancy rate was 61.1% （44/72） in the group of transfer at blastocyst stage （P〉0.05）. Conclusion Although the clinical pregnancy rate was not different between patients with freeze-thaw zygote and cleavage stage embryo transfer, higher survival rate for zygote was shown compared with that for cleavage stage embryo. However, the present studies did not demonstrate that extended culture thawing embryos to blastocyst could achieve favor clinical outcome.

Selection and Vitrification of Embryos with a Poor Morphological Score: A Proposal to Avoid Embryo Wastage

Embryos with a poor morphological score at cleavage stage are usually discarded because they are considered unsuitable for transfer and cryopreservation. This study examined the in vitro blastocyst development after extended culture of these embryos and the clinical outcomes after transfer of these blastocysts in warming cycles. A total of 597 blastocysts （24.7%） were obtained from 2421 embryos with low morphological scores after extended culture. One hundred and sixty blastocysts （6.6%） with optimal morphology were vitrified. Embryo utilization rate was increased from 30.8% to 32.6%. After warming, 61 out of 92 blastocysts （66.3%） survived and were transferred in 44 cycles. The clinical pregnancy rate and the implantation rate were 40.9% （18/44） and 32.8% （20/61） respectively. Thirteen healthy babies were born, and 5 pregnancies aborted spontaneously. Our study suggested that some blastocysts derived from embryos with a poor morphological score can be successfully vitrified and give rise to live births. Selection and vitrification of viable embryos after extended culture of embryos with a poor morphological score may constitute a proposal to avoid embryo wastage.

Clinical Outcomes of Transfer Vitrified-Thawed Day 4,8-Cell Embryos into Endometrium Prepared for Day 3 Embryos

Objective:To determine the clinical outcomes of transfer of day 3,8-cell embryos into endometrium prepared for day 3 embryos.Methods:This study performed a retrospective analysis of 1,190 retarded embryos.These embryos underwent extended culture in vitro to select and vitrify day 4,8-cell embryos,followed by 176 frozen embryo transfer cycles(study group),matching 660 transfer cycles with single frozen day 3,8-cell embryos as the control(control group).Results:The study group achieved successful implantation rates,clinical pregnancy rate,and live-birth rates(20.45%,15.91%,14.20%,respectively),although these were lower than that in the control group(30.45%,27.42%,and 20.91%;P=0.009,0.002,and 0.046,respectively).The miscarriage rate was similar to that in the control group(4.55%vs.3.33%,P>0.05),and the mean birth weight of the study group was higher than that in the control group(3,556±381 g vs.3,311±570 g,P=0.012).Conclusions:Transfer of frozen day 4,8-cell embryos into endometrial prepared for day 3 embryos can be a new and safe alternative for patients with delayed embryos.