What is Progesterone: Functions, Progesterone During Pregnancy

Progesterone is a steroid hormone that belongs to the group of progestin hormones . Although a small amount is also produced in men (testicular Leydig cells), progesterone is a typical female hormone.In women of childbearing age, it is secreted from the corpus luteum and placenta . The corpus luteum is formed following ovulation , when the follicle releases the egg cell it contains and is replaced by a cluster of cells with a characteristic yellow colour. The corpus luteum – under the stimulus of hypothalamic hormones (LH) – thus begins to produce progesterone, with the aim of preparing the body for pregnancy .

If fertilization does not occur, the corpus luteum regresses after a few days in the ovary. Reduction in progesterone levels leads to sloughing of the lining of the uterus ( endometrium ), then menstruation. In case of pregnancy, the placenta begins to produce progesterone which is associated with that synthesized by the corpus luteum of pregnancy.

Progesterone of natural origin or its synthetic derivatives are used in various fields ranging from the contraceptive pill to hormone replacement therapy , where micronized natural progesterone is used in combination with estrogen to lower the risk of developing an endometrial or breast carcinogenic pathology.

A curiosity

Progesterone is a thermogenic hormone , i.e. it favors an increase in  body temperature  (by about 0.5-1 degree). During the post-ovulatory phase (more or less from the 16th to the 26th day) women therefore burn much more calories than on the other days of the cycle (between 10 and 15% more).

What is Progesterone

Progesterone is the main progestogen hormone, as well as one of the most important for a woman’s metabolism and fertility. This hormone is mainly secreted by the corpus luteum in the ovaries during the second half of the menstrual cycle , but it is also produced:

  • In small quantities, from the adrenal glands ;
  • In pregnancy, from the placenta .


Progesterone plays important roles in the menstrual cycle and in maintaining the early stages of pregnancy.

What is progesterone used for?

The main functions of progesterone are:

  • Prepare the endometrium (internal lining of the uterus ) for the eventual nesting of the fertilized egg , transforming it from a proliferative to a secretory one (in practice, progesterone makes the uterine cavity more welcoming for the implantation of the embryo );
  • Once conception has occurred, help maintain gestation .

In fulfilling its role, progesterone is assisted by other female hormones and its concentration changes in relation to the phases of the menstrual cycle .

Progesterone During the Menstrual Cycle

The period preceding ovulation “prepares” the fertile phase of the menstrual cycle , giving rise to a sequence of events which ensures the maturation of the follicle destined to release the oocyte (ie the female gamete ), available for eventual fertilization . Ovulation is stimulated by the peak levels of estrogen and luteinizing hormone LH ), produced by the pituitary gland : it usually occurs 14 days before the start of the new menstrual cycle.

  1. In the FIRST PHASE of the menstrual cycle (called ESTROGENIC ), the hypothalamus secretes gonadotropin-releasing hormone ( GnRH ), in response to low estrogen concentration. This causes the pituitary to produce follicle-stimulating hormone ( FSH ), which stimulates the maturation of a dominant follicle, containing an egg cell destined to be fertilized. At the same time, the rising levels of estrogen in the body cause the uterine wall to thicken, through the accumulation of blood and nutrients (in this way, the fertilized egg cell will have the necessary support for its growth).
  2. Around the middle of the cycle, when maturation is complete, estradiol and luteinizing hormone ( LH ) stimulate the follicle to rupture and the egg cell is released into the fallopian tube , through which it travels to the uterus. This moment coincides with ovulation . From the remains of the dominant follicle that housed the egg cell, the so-called corpus luteum is formed , which produces progesterone . The SECOND PHASE of the cycle ( PROGESTINIC ) is more constant and lasts an average of 14 days.

In case of failed fertilization , the corpus luteum degenerates, the concentration of progesterone decreases and the oocyte is eliminated with the next menstruation . If conception occurs , the fertilized egg implants itself in the endometrium, 3 or 4 days after reaching the uterus; the corpus luteum continues to produce progesterone and the trophoblast that forms from the fertilized egg produces human chorionic gonadotropin ( hCG ). After a few weeks, PLACENTA replaces the corpus luteum as a source of progesterone, producing a relatively large amount of it throughout the rest of the physiological pregnancy .

Progesterone During Pregnancy

During PREGNANCY , progesterone:

  • Plays an important role in the development of the fetus (favors the implantation of the fertilized egg in the endometrium, stimulates the secretion of nutrients in the early stages, up to the “stabilization” of the placenta, decreases the maternal immune response to allow the physiological course of pregnancy etc.)
  • Stimulates the growth of maternal breast tissue ;
  • Inhibits lactation during pregnancy (note: the drop in progesterone levels after delivery is one of the triggers for milk production );
  • Strengthens the pelvic wall muscles in preparation for  labor .

Progesterone in Man

Progesterone is classically defined as a female hormone, but it is also produced in small quantities by Leydig cells , found in the testicles , where it appears to be involved in the production of sperm . In humans, progesterone measurements may be prescribed if specific adrenal pathologies are suspected.

See alsoProgesterone as a Drug: What is it for? When to use?

Progesterone dosage

Progesterone (Blood Test): What Does It Indicate And What Is It For?

The dosage of progesterone consists in measuring the concentration of the hormone in the blood , useful for understanding if there are menstrual cycle dysfunctions or inhibitions of ovarian activity .

Blood Test
If progesterone is produced in quantities that are not sufficient compared to the norm, the endometrium may not be suitable for the implantation of the fertilized egg cell or ovulation may not occur at all ( anovulatory cycle ). This can result in menstrual irregularities and difficulty conceiving. When gestation begins, however, low progesterone can be indicative of complications, such as ectopic pregnancy , placental abruption and risk of miscarriage.

The dosage of this hormone allows us to understand what are the underlying causes of these problems and to monitor that the pregnancy evolves normally.

This exam can be used:

  • To understand if ovulation has occurred : progesterone concentrations vary during the menstrual cycle and their determination allows us to ascertain if and when ovulation has occurred. To evaluate the change in hormone levels and establish when it coincides with the ovulatory phase , it is necessary to repeat the dosage several times during the menstrual cycle. Progesterone values ​​can also be measured to monitor the success of induced ovulation.
  • As an in-depth analysis in the case of infertility : progesterone dosage helps to recognize and manage some of the causes that hinder or cause some difficulty in conceiving.

Progesterone determination is also useful for monitoring:

  • Pregnancy : at the beginning of a pregnancy, the dosage of progesterone makes it possible to ascertain the correct functioning of the placenta and the state of health of the fetus. Usually, the test is performed in combination with the measurement of human chorionic gonadotropin (hCG). In the presence of symptoms suggestive of an ectopic pregnancy or a threat of miscarriage, however, the dosage of progesterone helps in the diagnosis, helping to establish whether the pregnancy is at risk.
  • Replacement therapy with progesterone : the dosage of the hormone allows you to periodically check its values, to evaluate the effectiveness of the therapeutic regimens set.

Finally, the measurement of progesterone helps to ascertain the cause of abnormal uterine bleeding in non-pregnant women.

Tests associated with the dosage of Progesterone

Progesterone is a parameter that is usually evaluated in combination with other parameters such as FSH (follicle stimulating hormone), LH (luteinizing hormone), hCG (human chorionic gonadotropin) and blood count .

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