Hormones play a significant role in regulating the timing of labor. Progesterone is crucial for maintaining pregnancy by keeping the uterine muscles relaxed. A decline in progesterone levels or its receptor activity can lead to the initiation of labor. Conversely, estrogen promotes the expression of contraction-associated proteins (CAPs) and oxytocin receptors, which facilitate uterine contractions.
Another hormone, corticotropin-releasing hormone (CRH), produced by the placenta, increases significantly as pregnancy progresses. Elevated levels of CRH are associated with preterm labor, as it stimulates the production of prostaglandins and the release of cortisol, which can induce labor.
