Fetal fibronectin (fFN) is a glycoprotein formed from the fetal cells that serves as a binder that glues the membrane and placenta to the decidua. Fetal fibronectin testing is used to screen for a woman’s risk of preterm birth. It is usually found in the cervical and vaginal secretions early in pregnancy (until 20-22 weeks) and again at or near term. If it appears too early, it suggests that labour may begin early, similarly to the way cardiac enzymes rises in the person with a myocardial infraction. Around 22 weeks, the chorion completely joins with the decidua, which blocks fibronectin from leaking into the vagina until term. Therefore, the presence of fetal fibronectin between 27 to 34 weeks can serve as an important marker of preterm birth.