What changes bring about induction of labor leading parturition?

Many factors are known to be involved in the process of labor, the sequences of events that induces and temporarily organizes labor:

• One model for the initiation of labor in the human suggests that as a result of the rising estrogen levels during gestation, the contraction of uterine OT receptors increases.
• Rapid fetal growth near term increase uterine distention which may also contribute to increase in uterine OT receptors near term.
• The increased number of OT receptors probably lower the threshold of the uterus to a level where myometrial contractions are initiated.
• Oxytocin may bind to decidual receptors and stimulate progesterone biosynthesis. The coupling of OT receptors activation and PG biosynthesis may be the crucial event in the initiation of labor.
• During spontaneous labor there is an increase in plasma OT levels in 6the fetal umbilical artery compared to umbilical vein, indicating a flow of OT from the fetus towards maternal compartment.
• Oxytocin derived from the fetus may provide the stimulus for the increased production of PGs at the onset of labor.
• Hypothalamoneurohypophysical maturation within the fetus, leading to fetal adrenal activation and a decline in progesterone biosynthesis as well as increased neurohypophysial hormone secretion, may provide final essential directive induction of parturition.