Table 1 Characteristic of studies included in our meta-analysis
| Studies | Country | Study design | Protocol | Sample size | The time of sample collection | Vd grouping criteria | Outcome measures | Main result | Main confounding factors |
|---|---|---|---|---|---|---|---|---|---|
| Anifandis et al. 2010 [8] | Greece | Retrospective cohort study |
Short agonist protocol IVF/ICIS | 101 | During oocyte retrieval |
< 20 ng/ml; 20.1-30 ng/ml; > 30 ng/ml | Clinical pregnancy rate (CPR) | Higher FF levels of 25(OH)D are associated with lower FF glucose levels and with lower CPR |
Age BMI Oocytes retrieved (n) |
| Rudick et al. 2012 [10] | USA | Retrospective cohort study |
Long agonist Flare-up GnRH-ant IVF/ICSI | 188 | After hCG administration |
< 20 ng/ml; 20-30 ng/ml; > 30 ng/ml | ou | Opposite relation between 25(OH)D levels and IVF outcomes by race |
Age BMI Embryos transferred (n, quality) Poor ovarian reserve |
| Firouzabadi et al. 2013 [14] | Iran | Prospective cohort study |
Long GnRH-a protocol IVF | 221 | On the day of ovum pick-up |
< 10 ng/ml 10-29 ng/ml 30-100 ng/ml | CPR | No significant association between FF or serum levels of 25(OH)D and CPR | None |
| Garbedian et al. 2013 [9] | USA | Prospective cohort study |
Long GnRH-a Flare-up GnRH-ant IVF | 162 | Before oocyte retrieval |
< 75 nmol/l ≥75 nmol/l | CPR | High vitamin D level was related to higher CPR |
Age BMI Day 5[v. day3] embryo transfer |
| Fabris et al. 2014 [17] | Spain | Retrospective cohort study | Egg donation recipients | 267 | After 2 weeks of HRT |
< 20 ng/ml; 20-30 ng/ml; > 30 ng/ml |
CPR; Ongoing pregnancy rate | Low vitamin D level was not related to decreased CPR with egg donation. | BMI |
| Paffoni et al. 2014 [12] | Italy | Prospective cohort study |
Long GnRH-a Flare-up GnRH-ant IVF | 335 | Prior to to initiation of COH |
< 20 ng/ml; ≥20 ng/ml |
CPR; Implantation rate | High vitamin D level was related to higher CPR |
Race BMI |
| Polyzos et al. 2014 [13] | Belgium | Retrospective cohort study |
Irrespective of the protocol Single, blastocyst IVF/ICSI | 368 | On the day of hCG administration |
< 20 ng/ml; ≥20 ng/ml |
Chemical PR CPR; Live birth rate (LBR) | Low vitamin D level was related to lower clinical pregnancy rate and live birth rate | Season of embryo transfer |
| Rudick et al. 2014 [11] | USA | Retrospective cohort study | Egg donation recipients | 99 | At the time of down-regulation |
< 20 ng/ml; 20-30 ng/ml; > 30 ng/ml |
CPR; LBR | Higher 25(OH)D levels associated with higher CPR and LBR |
Recipient age Recipient BMI Embryos transferred(n, quality) |
| Franasiak et al. 2015 [18] | Canada | Retrospective cohort study |
Long GnRH-a Flare-up GnRH-ant FET/ICSI | 517 | On the day of ovulation trigger |
< 20 ng/ml; 20-30 ng/ml; > 30 ng/ml |
CPR Ongoing PR | Vitamin D had no relationship with IVF outcomes |
Age No. of embryo transferred Race |