Progesterone supplementation also improves pregnancy rates OR 1.77 (1.09–2.81) (van der Linden et al. 2015) and as this does not stimulate VEGF the risk of OHSS is lower when compared to luteal support with hCG, OR 0.46 (0.30–0.71) (van der Linden et al. 2015). This evidence concerns the gene VEGFA and ovarian hyperstimulation syndrome.