Parturition does not occur in transgenic mice lacking the prostaglandin F receptor (Ptgfr^−/−) because luteolysis is forestalled and progesterone production persists. Ovariectomy of pregnant Ptgfr^−/− mice leads to a decline in circulating progesterone and delivery of live pups. The objective of the present study was to test the hypothesis that immigration of macrophages and increased innervation of the cervix of Ptgfr^−/− mice was associated with ripening and parturition. The cervix of pregnant Ptgfr^−/− mice was studied on Days 15–21 after breeding; additional groups were ovariectomized on Day 19 of pregnancy, and the cervix obtained on Day 20 of pregnancy before birth or the next day at about 24 h after birth. On Days 18–19 of pregnancy, macrophage numbers and nerve fiber density increased more than 3-fold compared with findings in nonpregnant or Day 15 or 21 pregnant Ptgfr^−/− mice. The magnitude and time course of these changes were comparable to those found in wild-type controls that delivered on Day 19 after breeding. Thus, the mechanism regulating macrophage immigration, innervation, and cervical remodeling in Ptgfr^−/− mice with delayed parturition is similar to wild-type controls that deliver at term. By contrast, ovariectomy forestalled the decrease in cervical macrophages in Ptgfr^−/− mice. By Day 21 after breeding, macrophage numbers more than double those after ovariectomy, relative to those found in pregnant Ptgfr^−/− mice, whereas nerve fiber density was the same regardless of birth. Density of collagen structure in these mice directly matched macrophage traffic in the cervix. The findings indicate that the prostaglandin F_2alpha receptor and progesterone withdrawal are a necessary part of the final common pathway for ripening of the cervix and the process of parturition.