EC Gynaecology

Stimulated frozen embryo transfer cycles (FET), also called hormone replacement (HRT) FET cycles, utilise a high dose of oestrogen from the start of a natural menstrual cycle. This helps to build the endometrium and suppress ovulation. Suppression of ovulation is caused by suppressing follicle-stimulating hormone (FSH) and luteinising hormone (LH) from the anterior pituitary. Escape ovulation, which is unexpected follicular development in HRT-FET, is uncommon but an event that happens on a regular basis. This inevitably influences the timing of the embryo transfer hence the outcomes.

Escape ovulation is an event which can be encountered in 1.9 - 7.4% of HRT-FET cycles without pituitary suppression [1] either with gonadotrophin agonists (GnRH-a) or antagonists. If recognised, escape ovulation leads to the cancellation of the treatment. If unrecognised, however, it would directly affect the outcome and influence the pregnancy rates due to possible mistiming of the embryo transfer (ET). Recognising or avoiding escape ovulation may therefore improve the outcomes in HRT-FET cycles.

1. Van de Vijver A., et al. “Cryopreserved embryo transfer in an artificial cycle: Is GnRH agonist down-regulation necessary?” Reproductive BioMedicine Online 5 (2014): 588-594.
2. Bocca S., et al. “Impact of serum estradiol levels on the implantation rate of cleavage stage cryopreserved-thawed embryos transferred in programmed cycles with exogenous hormonal replacement”. Journal of Assisted Reproduction and Genetics 3 (2015): 395-400.
3. Mackens S., et al. “Frozen embryo transfer: a review on the optimal endometrial preparation and timing”. Human Reproduction 32 (2017): 2234-2242.
4. Keltz MD., et al. “Baseline cyst formation after luteal phase gonadotropin-releasing hormone agonist administration is linked to poor in vitro fertilisation outcome”. Fertility and Sterility3 (1995): 568-572.
5. El-Toukhy T., et al. “Pituitary suppression in ultrasound-monitored frozen embryo replacement cycles. A randomised study”. Human Reproduction4 (2004): 874-879.