(i) The endometrium, which proliferates under the influence of estrogens, becomes a secretory structure under the influence of progesterone. The endometrial glands become elongated and coiled and secrete a glycogen-rich fluid. It also converts the Secretory endometrium of the luteal phase of the menstrual cycle to the decidua during pregnancy. Progesterone is essential for implantation and maintenance of the decidua.
(ii) In the cervix, the mucus secreted becomes thick and viscid under the influence of progesterone. This consistency of cervical mucus indicates that ovulation and luteinization have occurred,
(iii) In the myometrium, progesterone inhibits uterine motility by hyperpolarization of the uterine myometrium,
(iv) In the breast, progesterone promotes lobuloalveolar growth in the mammary gland,
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(v) In the fetus, progesterone contributes to the growth and development by acting as a precursor for corticosteroid synthesis by the fetal adrenal cortex.