Higher estradiol dose may boost IVF success in frozen embryo transfers

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

* Inclusion Criteria * Women aged 18-40 years. * Body mass index \<30 kg/m². * First autologous programmed HRT-FET cycle. * Endometrial preparation planned using oral estradiol valerate only. * Vitrified embryos derived from a previous autologous IVF or ICSI cycle. * Planned transfer of vitrified-warmed day-5 blastocyst(s). * Normal uterine cavity documented within the preceding 12 months. * Baseline transvaginal ultrasonography on cycle day 2 or 3 showing no ovarian cyst, dominant follicle, or intracavitary pathology. * Ability and willingness to provide written informed consent. * Ovulatory-factor infertility, including polycystic ovary syndrome, will be eligible provided all other criteria are fulfilled. * Exclusion Criteria * Contraindication to estrogen treatment * History of breast cancer or endometrial cancer * History of deep venous thrombosis, pulmonary embolism, or stroke * Allergy to the study medication * Irregular vaginal bleeding * Thyroid disorder * Hyperprolactinemia * Uncontrolled diabetes mellitus * Uncontrolled hypertension * Significant liver disease * Significant kidney disease * Severe systemic illness * Uterine abnormality * Untreated hydrosalpinx * Untreated pathology inside the uterine cavity * Donor-oocyte cycle * Donor-embryo cycle * Gestational-carrier cycle * Preimplantation genetic testing for aneuploidy (PGT-A) cycle * Natural cycle or modified natural cycle for endometrial preparation * Use of transdermal, vaginal, or mixed estrogen regimens * Use of letrozole, gonadotropins, or GnRH agonists for endometrial preparation * Premature ovarian insufficiency * Stage III or IV endometriosis * Recurrent implantation failure * Recurrent miscarriage * Abnormal parental karyotype * Active smoking * Difficult embryo transfer * Refusal to participate