Several biochemical pathways are implicated in the onset of labor. The prostaglandin synthesis pathway is particularly important. Prostaglandins are lipid compounds that have hormone-like effects and can induce uterine contractions. Enzymes such as cyclooxygenase (COX) catalyze the conversion of arachidonic acid to prostaglandins. Elevated levels of prostaglandins can lead to the initiation of labor, including preterm labor.