CXCL12 and placenta praevia: CXCL12, CXCR4, and CXCR7 levels in placental tissues were evaluated by IHC (Figure 1a and b), and the findings demonstrated that brownish-yellow staining was seen in the cytoplasm of both syncytiotrophoblasts and cytotrophoblasts in the placental tissues of pregnant women with placenta previa.