Study Inclusion adn Exclusion Criteria

from november 2018 to December 2019, 375 patients undergoing IVF at the Reproductive Medicine Center of Shiyan people’s Hospital Affiliated to Hubei University of Medicine were analyzed. All patients received treatment with the follicular-phase GnRH agonist protocol. Serum vitamin B12 levels were measured using chemiluminescence before therapy began. After applying inclusion and exclusion criteria, 356 patients were included in the final analysis.

Inclusion Criteria

Patients were included if they met the following criteria: aged 20-45 years; diagnosed with infertility; undergoing their first IVF cycle; and had an AMH level of 1.0-4.0 ng/mL.We used this AMH range to avoid including patients with diminished ovarian reserve (DOR) or polycystic ovary syndrome (PCOS), as the literature consistently reports AMH levels above 1 ng/ml for normal ovarian reserve and between 3.5-5 ng/ml for PCOS [9, 10].

Exclusion Criteria

Patients were excluded if they had severe medical conditions (e.g., hypertension, diabetes, gastrointestinal diseases); an indication for preimplantation genetic testing (PGT); other endocrine disorders affecting metabolism (e.g., thyroid disease, hyperprolactinemia); or had taken vitamin B supplements within 3 months prior to inclusion.

The study was approved by the Ethics Committee of Renmin Hospital, Hubei University of Medicine, and informed consent was obtained from all couples. All methods were performed in accordance with relevant guidelines and regulations.

to explore potential non-linear relationships, we divided the study population into three equal groups based on serum vitamin B12 levels using tertile division [11].