Embryo cryopreservation and frozen-thawed embryo transfer refers to the procedures whereby embryos are cryopreserved for storage, to be thawed and transferred at a later stage after the conclusion of the stimulated cycle. Frozen-thawed embryo transfer has become a routine ART practice and the proportion of frozen-thawed embryo transfer among embryo transfer cycles has increased worldwide. Progesterone plays a vital role in both conception and the maintenance of pregnancy; as such, it has been a central focus of investigation aimed at optimizing hormonal replacement therapy.
The beginning of P administration is critical. Starting too soon could lead to prematureluteinizationandstartingtoolatecouldincreaseuterinecontractility, which is negatively related to P quantity and increased uterine contractions on the day of embryotransfer leading to lower implantation rates
Ideally, progesterone (p4) monitoring would be tailored to the administration method; however, given the significant practical difficulties in obtaining endometrial progesterone levels, serum P4 concentrations continue to be the mainstay marker for P4 monitoring.