Extended Culture of Day 3 Embryos Improves Live Birth Rate in In Vitro Fertilization-Embryo Transfer
In vitro fertilization-embryo transfer (IVF-ET) is a widely used assisted reproductive technology that has helped millions of couples achieve pregnancy. However, despite advancements in the field, implantation rates remain relatively low, typically ranging between 20% to 30%. One of the critical challenges in IVF-ET is the selection of embryos with the highest developmental potential for transfer. Traditionally, embryos are evaluated based on morphological criteria and transferred on the morning of day 3 post-fertilization. This stage of development is crucial because it marks the transition from maternal to embryonic control, known as embryonic genome activation (EGA). Embryos that successfully initiate EGA are more likely to develop further and implant, while those that fail to activate their genome often undergo developmental arrest.
This study explores a novel strategy to improve live birth rates in IVF-ET by extending the culture of day 3 embryos for an additional 7 to 8 hours. The rationale behind this approach is that embryos with sustainable developmental potential (SDP) will continue to develop during this extended culture period, allowing for better selection of viable embryos for transfer. The study retrospectively analyzed the pregnancy outcomes of patients undergoing IVF-ET treatment at the Center for Reproductive Medicine of the 940th Hospital of the Joint Logistics Support Force of the Chinese People’s Liberation Army between January 2012 and December 2017. The findings suggest that extended culture of day 3 embryos significantly improves live birth rates, offering a promising strategy to enhance the success of IVF-ET treatments.
Embryonic Development and Embryonic Genome Activation
Embryonic development at the early cleavage stage is a complex biological process regulated primarily by maternal factors. On day 3 post-fertilization, the embryonic genome begins to activate, marking a critical transition in development. Embryos that successfully initiate EGA are more likely to continue developing and implant, while those that fail to activate their genome often undergo developmental arrest. However, identifying embryos that have initiated EGA is challenging, as morphological criteria alone are insufficient to predict developmental potential. This limitation contributes to the relatively low implantation rates observed in IVF-ET.
Study Design and Methodology
The study included 963 oocyte retrieval cycles from women under 38 years of age with normal ovarian reserves and at least two available embryos on the morning of day 3 post-insemination. The embryos were divided into two groups: the extended culture (EC) group and the control group. In the EC group, embryos were graded at 08:00 to 09:00 on day 3 and then continuously cultured for an additional 7 to 8 hours until 16:00. Embryos that showed an increased blastomere number during this extended culture period, combined with conventional morphological criteria, were considered to have SDP and were preferred for transfer. In the control group, embryos were evaluated once at 08:00 to 09:00 on day 3, and the best-quality embryos were transferred immediately.
Clinical pregnancy was confirmed by the presence of a gestational sac with a fetal heartbeat detected via transvaginal ultrasound examination five weeks after embryo transfer (ET). Patients were followed up via telephone, and those with live births were monitored for seven days after delivery. Perinatal and neonatal outcomes were evaluated, including deliveries after 28 weeks of gestation and perinatal and neonatal mortality.
Results
The study found that 57.63% of embryos in the EC group continued to develop during the extended culture period, demonstrating SDP. Clinical pregnancy outcomes, including clinical pregnancy rates, implantation rates, and live birth rates, were significantly better in the EC group compared to the control group. The total clinical pregnancy rate in the EC group was 55.04%, compared to 48.98% in the control group. Similarly, the total live birth rate was 46.29% in the EC group, significantly higher than the 37.95% observed in the control group. The total implantation rate was also higher in the EC group (34.48% vs. 29.67%).
Moreover, the rates of live newborn infants per ET cycle and per transferred embryo were significantly higher in the EC group. The live newborn infant rate per ET cycle was 59.35% in the EC group, compared to 48.64% in the control group. Similarly, the live newborn infant rate per transferred embryo was 28.61% in the EC group, compared to 22.75% in the control group. However, there was no significant difference in the cumulative live birth rates between the two groups (68.27% vs. 66.01%).
The study also found that the number of ET cycles and the number of embryos transferred were significantly reduced in the EC group compared to the control group. Kaplan-Meier survival analysis showed that while the cumulative probability of achieving one live birth was similar in both groups, the time to achieve one live birth was shorter in the EC group.
Discussion
The findings of this study suggest that extending the culture of day 3 embryos for an additional 7 to 8 hours can significantly improve live birth rates in IVF-ET. This strategy allows for the identification of embryos with SDP, which are more likely to have initiated EGA or have the potential to do so. By selecting these embryos for transfer, the overall success rate of IVF-ET can be enhanced.
The extended culture period provides a short window for viable embryos to demonstrate their developmental potential. Embryos that continue to develop during this period are more likely to be viable and capable of successful implantation. This approach is particularly advantageous because it does not require the extended culture period needed for blastocyst formation, which typically takes 48 to 72 hours. Additionally, only 3.35% of embryos in the EC group were deemed ineligible for transfer and discarded, compared to the approximately 50% of embryos that fail to reach the blastocyst stage in traditional blastocyst culture.
The study also highlights the importance of sustainable developmental competence as a key indicator of embryo viability. Embryos that do not cleave during the preceding 24 hours are typically considered to be in developmental arrest and are not recommended for transfer. However, the extended culture strategy allows for the identification of embryos with SDP, which may still possess some developmental potential even if they do not show an increased blastomere number during the extended culture period.
Conclusion
In conclusion, the extended culture of day 3 embryos offers a viable strategy to improve live birth rates in IVF-ET. By providing a short window for embryos to demonstrate their developmental potential, this approach allows for the selection of embryos with higher viability, leading to improved clinical outcomes. The strategy is particularly advantageous because it does not require the extended culture period needed for blastocyst formation and results in a lower rate of embryo discard. Overall, the extended culture of day 3 embryos represents a promising advancement in the field of assisted reproductive technology, offering hope to couples seeking to achieve pregnancy through IVF-ET.
doi.org/10.1097/CM9.0000000000000901
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