Clinical Research Directory

Inclusion Criteria: * HRT-FET cycles performed during the prespecified retrospective study period * Women aged 18 to \<42 years at the time of embryo transfer * BMI \<30 kg/m² * Transfer of at least one good-quality embryo * Serum progesterone measured on the morning of embryo transfer as part of routine care * Availability of the primary clinical pregnancy outcome in the medical record Exclusion Criteria: * Severe or uncontrolled endocrine disorders documented at the time of treatment (e.g., thyroid dysfunction or premature ovarian insufficiency) * Untreated severe uterine factors likely to impair implantation (e.g., severe endometriosis, large or subendometrial fibroids, intrauterine adhesions, or endometrial polyps) * Missing or implausible key exposure data after source-data verification