Rescue Progesterone Supplementation During Frozen Embryo Transfer

Inclusion Criteria: * Women 18-42 years of age * Normal uterine cavity (according to treating physician) * FET substituted cycle prescribed * First or second cycle of FET * Adequate endometrial pattern (triple layer) and thickness (\>7 mm) after adequate standard endometrial preparation in artificial cycle Exclusion Criteria: * Any uterine abnormalities confirmed by treating physician making participant unable to proceed with FET * Patients with personalized FET according to the endometrial receptivity assay tests * Previous allergic reactions to progesterone or any of the ingredients of Endometrin * Severe hepatic dysfunction or disease * Known or suspected breast cancer or genital tract cancer * Known active arterial or venous thromboembolism or severe thrombophlebitis or cerebro-vascular disease, or a history of these events * Diagnosed porphyria * Undiagnosed abnormal vaginal bleeding * Known missed abortion or ectopic pregnancy * Recurrent pregnancy loss excluding biochemical pregnancies * Hypersensitivity to Acetylsalicylic acid (ASA), salicylates, non-steroidal anti-inflammatory drugs (NSAIDs), analgesics, antipyretics or other ingredients in the product or component of the container * Acute gastrointestinal ulcer, history of gastrointestinal ulcers and hemorrhagic diathesis * Active or severe renal disease, or congestive heart failure * History of asthma induced by salicylates or other NSAIDs * Use of methotrexate at doses of 15mg/week or more * Glucose-6-phosphate dehydrogenase (G6PD) deficiency