Effect of vitamin D supplementation on assisted reproduction technology (ART) outcomes and underlying biological mechanisms: protocol of a randomized clinical controlled trial. The "supplementation of vitamin D and reproductive outcome" (SUNDRO) study.

The protocol was included in EudraCT on 22nd September 2015 with the registration number assigned ' 2015-004233-27 '; it was submitted through the database of the Italian "Osservatorio Nazionale della Sperimentazione Clinica (OsSC)" - (National Monitoring Centre of Clinical Trials) to the National Competent Authority on 8th March 2016 and approved on 23rd June 2016.