When the egg oocyte is released from the ovary, it undergoes a process of maturation. Following maturation, the egg awaits fertilization by the sperm in the fallopian tube. (In an assisted reproduction setting, this maturation is done in vitro, that is, in contained culture media. An optimal window, the fertility window, exists in which fertilization should occur, and this is generally within 10 hours of ovulation. In the event no fertilization occurs within this time frame, oocytes experience a process of degradation referred to as “post-ovulatory ageing.”
The cellular deterioration associated with postovulatory ageing can strongly influence the outcome of fertilization in vivo and in vitro, as the oocyte provides factors to the embryo that orchestrate the early events of embryo development (embryogenesis), including repair of damage to the DNA of both egg and sperm. Since there are no visual signs of ovulation—and, as a result, no mechanisms in place to ensure synchrony between intercourse and release of the oocyte—there is an increased likelihood fertilization can involve an aged oocyte and freshly ejaculated sperm. This can result in the generation of poor quality embryos and an increased likelihood of pregnancy loss. Identifying your fertility window can help you avoid late fertilization.