Progesterone is a steroidal hormone mainly secreted by the corpus luteum after ovulation, but also in small amounts by the adrenal glands and placenta during pregnancy. It plays an essential role in regulating the menstrual cycle, preparing the endometrium for embryonic implantation, and maintaining pregnancy.
During the follicular phase of the menstrual cycle, progesterone levels are low, allowing the growth and maturation of ovarian follicles under the influence of estrogens and FSH. After ovulation, remaining follicular cells turn into luteal cells under the action of LH, forming the corpus luteum. The luteal cells then acquire the ability to secrete large amounts of progesterone, which gradually increases during the luteal phase to reach a peak about 7 days after ovulation.
Progesterone mainly acts on the uterine endothelium, stimulating its secretory transformation. Under the influence of progesterone, endometrial glands become tortuous and secrete a glycogen-rich mucus, necessary for the nourishment of the embryo in case of implantation. Progesterone also promotes the development and coiling of spiral arteries, thus increasing the vascularization of the endometrium.
In case of fertilization and embryonic implantation, the trophoblastic cells of the embryo secrete the hormone human gonadotropic chorionic (hCG) which sustains the corpus luteum and stimulates its production of progesterone. Maintaining a high level of progesterone is essential to ensure the development of pregnancy, promoting endometrial growth, inhibiting uterine contractions, and modulating the maternal immune response to prevent embryo rejection. The gestational corpus luteum ensures the secretion of progesterone until the placenta takes over, around the 8th week of pregnancy.
In the absence of fertilization, the corpus luteum involutes after about 14 days, causing a sharp drop in progesterone levels. This progesterone deprivation triggers the desquamation of the endometrium and the onset of menstruation, marking the beginning of a new cycle.
Progesterone also exerts a negative feedback on the hypothalamic-pituitary axis, inhibiting the pulsatile secretion of GnRH and LH. This feedback helps to slow follicular growth and prevent the recruitment of new follicles during the luteal phase, thus ensuring mono-ovulation in women.
Anomalies in the secretion or action of progesterone can disrupt luteal function and impair fertility. Luteal insufficiency, characterized by a progesterone deficiency and/or a length of the luteal phase less than 10 days, can impair the quality of the endometrium and prevent embryonic implantation. It may be due to a defect in follicular development, delayed ovulation, or premature luteolysis. The treatment of luteal insufficiency relies on progesterone supplementation in the second part of the cycle, orally, vaginally, or intramuscularly.
Progesterone is also used in assisted reproductive treatments to support the luteal phase and promote embryonic implantation after ovarian stimulation and in vitro fertilization. It is also prescribed early in pregnancy in women with a history of recurrent miscarriage, although its effectiveness in this indication remains controversial.
In addition to its role in reproduction, progesterone has sedative and anxiolytic properties by acting on the GABA receptors of the central nervous system. It can thus modulate mood and behavior and is involved in certain psychological disorders such as premenstrual syndrome or post-partum depression.
Understanding the role of progesterone in regulating the menstrual cycle and maintaining pregnancy is essential to comprehend the mechanisms of human reproduction and manage fertility disorders and pregnancy complications. Progesterone dosage in the second part of the cycle is a commonly performed test to evaluate the quality of ovulation and luteal function, and monitor the response to ovary stimulation treatment or luteal supplementation.
Key takeaways :
– Progesterone is a steroidal hormone mainly secreted by the corpus luteum after ovulation, playing an essential role in the regulation of the menstrual cycle, the preparation of the endometrium for embryonic implantation, and pregnancy maintenance.
– After ovulation, the remaining follicular cells turn into luteal cells under the action of LH, forming the corpus luteum which secretes large quantities of progesterone.
– Progesterone acts on the uterine endometrium, stimulating its secretory transformation, promoting the development of spiral arteries and increasing vascularization.
– In case of fertilization, progesterone is kept at a high level to ensure pregnancy development, by inhibiting uterine contractions and modulating the maternal immune response.
– In the absence of fertilization, the sharp drop in progesterone due to the involution of the corpus luteum triggers menstruation.
– Progesterone exerts a negative feedback on the hypothalamic-pituitary axis, slowing follicular growth during the luteal phase.
– Luteal insufficiency, characterized by a deficit in progesterone, can damage the quality of the endometrium and prevent embryonic implantation. Its treatment relies on progesterone supplementation.
– Progesterone is used in assisted reproduction treatments to support the luteal phase and foster embryonic implantation.
– Progesterone dosage in the second part of the cycle is a commonly performed test to evaluate the quality of ovulation and luteal function.
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