Progesterone (P4) and estradiol-17β (E2) play critical and opposing roles in regulating myometrial quiescence and contractility during pregnancy and labor.While these contrasting hormonal effects are likely mediated via differential regulation of inflammatory and contractile genes, the underlying mechanisms remain incompletely understood.We have discovered that transcription factors ZEB1 and ZEB2, which are targets of the microRNA (miRNA/miR) 200 family, serve as P4/progesterone receptor (PR)-mediated regulators of uterine quiescence during pregnancy.We also recently found that levels of the clustered miRNAs, miR-199a-3p and miR214, were significantly decreased in laboring myometrium of pregnant mice and humans and in an inflammatory mouse model of preterm labor, while the miR-199a-3p/miR-214 target, cyclooxygenase-2 (COX-2), a critical enzyme in synthesis of contractile prostaglandins, was coordinately increased.