Fetal signals are crucial in the timing of labor. The fetal hypothalamic-pituitary-adrenal (HPA) axis becomes activated as the fetus matures, leading to the production of cortisol. Cortisol accelerates fetal lung maturation and stimulates the production of enzymes that convert progesterone to estrogen in the placenta. This hormonal shift contributes to the initiation of labor.
Additionally, the release of fetal fibronectin, a glycoprotein found at the maternal-fetal interface, can disrupt the extracellular matrix and signal the onset of labor. Elevated levels of fetal fibronectin in vaginal secretions are often used as a marker for the risk of preterm labor.
