Progesterone maintains pregnancy and it also used in contraceptive pills. Why? 

UnknownFemale reproductive system regulates the hormonal changes responsible for puberty and for an adults reproductive function. Dynamic integration of hormonal signals from the hypothalamus, pituitary, and ovary, result in repetitive cycles of follicle development, ovulation, and preparation of the endometrial lining of the uterus for implantation should conception occur. This could be by one extensive explanation , define a Normal Reproductive Function in women.

The ovary orchestrates the development and release of a mature oocyte and also elaborates hormones (e.g., estrogen, progesterone, inhibin, relaxin) that are critical for pubertal development and preparation of the uterus for conception, implantation, and the early stages of pregnancy. To achieve these functions in repeated monthly cycles, the ovary undergoes some of the most dynamic changes of any organ in the body.

Understand a reproductive cycle as below. Please note the level of the hormones.

The levels of Progeterone (Prog) start increasing during the ovulation or through the luteal phase and then lays low.

When we substitute the progesterone in many women as oral pills (likely desogestrel ), the body is likely to confused to feel and accept that the conception has occurred and its main function in the cycle is to stop production of an egg (prevent Ovulation). The rest of the steps are the same as explained below. However when you stop the pills (Oral), the usual initiations and proceedings towards a follicular phase are likely to take place and bleeding begins as part of the normal menstrual cycle.

You may also note that the combined actions of estrogen and progesterone are responsible for the secretory changes in the endometrium that are necessary for implantation (Support Conception). The corpus luteum is supported by LH but has a finite life span because of diminished sensitivity to LH. The demise of the corpus luteum results in a progressive decline in hormonal support of the endometrium. Inflammation or local hypoxia and ischemia result in vascular changes in the endometrium leading to the release of cytokines, cell death, and shedding of the endometrium.

Now in case of Pregnancy (If conception occurs), hCG produced by the trophoblast binds to LH receptors on the corpus luteum, maintaining steroid hormone production and preventing involution of the corpus luteum. The corpus luteum is essential for the hormonal maintenance of the endometrium during the first 6–10 weeks of pregnancy until this function is taken over by the placenta.

Wish it answers the query.

Source: Puneet Chandna’s answer to Progesterone maintains pregnancy and it also used in contraceptive pills. Why? – Quora

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