Somigliana E, Sarais V, Reschini M, et al. - Researchers conducted a 2-center randomized superiority double-blind placebo-controlled trial, the “supplementation of vitamin D and reproductive outcome” trial, to investigate if improved clinical pregnancy is achieved with oral vitamin D ₃ supplementation in females undergoing an in vitro fertilization cycle. A total of 630 women were randomly assigned 2 to 12 weeks prior to the start of the in vitro fertilization cycle to receive either a single dose of 600,000 IU of vitamin D ₃ (n = 308) or placebo (n = 322). A clinical pregnancy was achieved in 113 (37%) and 130 (40%) women in the treatment and placebo groups, respectively. Findings revealed that no improvement in the rate of clinical pregnancy was conferred by a single oral dose of 600,000 IU of vitamin D ₃, in women with normal weight with preserved ovarian reserve and low vitamin D concentrations undergoing in vitro fertilization cycles. These data do not favor vitamin D ₃ supplementation to improve in vitro fertilization success rates but further investigations are needed to rule out milder but potentially interesting benefits.