Parturition is vaginal delivery of the fetus at term, about 40 weeks from the last menstrual period (38 weeks from ovulation).
Delivery between the 28th and the completed 37th week of gestation defines a premature infant.
Preparation for Parturition
In the last weeks of pregnancy, rising estrogen increases myometrial connexin synthesis, forming gap junctions that coordinate myometrial contraction.
Estrogen also induces synthesis of oxytocin receptors in the myometrium, enhancing uterine smooth muscle contraction.
The cervix softens through enzymatic lysis of its collagen fibers; relaxin, secreted from the placenta and ovaries, facilitates cervical softening and dilation.