Vitamin D is best known for keeping our bones healthy, but growing research suggests it may also play a role in fertility. Many IVF clinics now routinely check vitamin D levels and prescribe supplements before treatment, but the science is still unclear on whether this actually improves the chances of pregnancy.

Our study, based in the UAE, aims to find out whether a woman's vitamin D level on the day of her frozen embryo transfer (FET) makes a difference to whether she becomes pregnant and delivers a baby. The UAE is an ideal setting for this research, as vitamin D deficiency is particularly common in the region. The findings could shape how fertility clinics screen and treat women seeking fertility treatment in the future.

Serum vitamin D3 has attracted growing research interest for its potential role in female reproductive physiology. While some studies associate sufficient D3 levels with improved IVF outcomes, others have failed to confirm this, leaving the evidence base contested. Despite this uncertainty, pre-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 D3-insufficient women receiving supplementation and 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 centre. 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.

Biological female

Women undergoing FET cycle who do not suffer from conditions affecting implantation and have got vitamin D levels tested 3 - 6 months before FET cycle.

Not an NIH project