Song et al. found decreased CXCL12 gene expression in women with severe preeclampsia in preterm pregnancy compared with healthy pregnant women [36]. In vitro experiments in sheep showed that stimulation of trophoblast cells with CXCL12 increased the expression of mRNA for vascular endothelial growth factor and fibroblast growth factor 2, which are important for placentation [37]. This evidence concerns the gene CXCL12 and preeclampsia.