With the recent trend toward single embryo transfer (ET), cryopreservation of extraneous embryos is becoming increasingly prevalent. Several replacement protocols for frozen-thawed ET (FET) exist, with no advantage of one protocol over the others. All consecutive patients undergoing natural cycle Day-3 FET cycles between May 2012 and March 2015 in our IVF unit were evaluated. While following spontaneous ovulation, all patients received progesterone luteal support. Since June 2014, patients underwent the same aforementioned natural cycle FET cycles, with two additional injections, one of recombinant hCG (250 mcg) and the other of GnRH-agonist (triptorelin 0.1 mg), on the day of transfer and 4 d later, respectively. While the patients' clinical characteristics, the prevalence of embryos that survived the thawing process and the number of embryos transferred were comparable between the earlier as compared with the later period, implantation rate, positive β-hCG, clinical, and ongoing pregnancy rates were significantly higher during the later period. We, therefore, suggest that when natural cycle FET is offered, the addition of two injections of recombinant hCG and GnRH-agonist, on the day of transfer and 4 d later, respectively, might increase clinical pregancy rates. Further large prospective studies are needed to elucidate the aforementioned recommendation prior to its routine implementation.
Keywords: Cryopreservation; GnRH-agonist; IVF; frozen-thawed embryo transfer; hCG; luteal support; outcome; pregnancy rate.