An Investigation of the Effect of Vitamin D Level During Frozen Embryo Transfer (FET) in IVF and Pregnancy Outcomes

Serum vitamin D3 has attracted growing research interest for its potential role in female reproductive physiology. While some studies associate sufficient vitamin D3 levels with improved IVF outcomes, others have failed to confirm this, leaving the evidence base contested. Despite this uncertainty, pre-In vitro fertilization (IVF) vitamin D screening and supplementation of insufficient patients has become widespread clinical practice. Evidence specific to frozen embryo transfer (FET) cycles remains particularly limited. Recent prospective studies found no significant difference in ongoing pregnancy, live birth, or implantation rates between vitamin D3-insufficient women receiving supplementation and vitamin D3-replete women who did not, underscoring the need for higher-quality, targeted research. While emerging data support a role for vitamin D in endometrial receptivity, it remains unclear whether correcting insufficiency prior to FET meaningfully improves reproductive success.

To address these gaps, our study will evaluate the association between serum vitamin D3 levels on the day of FET and subsequent pregnancy and delivery outcomes at a UAE fertility center. Supplementation history and relevant clinical variables will be captured via patient questionnaire. Vitamin D status will be classified per International Society of Endocrinology guidance: deficient (<20 ng/mL), insufficient (20-29 ng/mL), and sufficient (≥30 ng/mL). Given the high regional prevalence of vitamin D deficiency, this study is well-positioned to determine whether vitamin D status represents a modifiable determinant of reproductive success, with direct implications for clinical screening and management protocols in this population.

Inclusion:

• Women undergoing frozen embryo transfer (FET) at Fakih IVF.
• Age between 18 and 40 years.
• Body mass index (BMI) between 18 and 40 kg/m².
• Patients who had serum vitamin D levels assessed within three months prior to FET
• Supplementation with Vitamin D if deficient < 30 ng/mL (75 nmol/L).

Exclusion:

• Age below 18 years or above 40 years.
• BMI below 18 kg/m² or above 40 kg/m².
• Patients who did not have vitamin D levels measured within three months prior to FET.
• Patients who were found to have low vitamin D levels but did not receive supplementation.
• Patients with recurrent implantation failure (RIF).
• Patients with known uterine factors affecting implantation (e.g., congenital uterine anomalies, intrauterine adhesions, submucosal fibroids).
• Patients with significant medical comorbidities that may affect pregnancy outcomes.