fertility-health > health > female-health > hormones > estrogen-and-progesterone

Fertility HealthFertility Conditons
Fertility TreatmentsStart you fertility journey

Estrogen and Progesterone

Estrogen and progesterone are the two main female sex hormones, and they’re made by specialised cells in the ovaries. The changing levels of these two steroidal hormones determine the length and health of a woman’s menstrual cycle by altering:

  1. The function of the ovaries
  2. Growth and receptivity of the uterus lining
  3. Shape and function of the cervix
  4. Body’s basal body temperature (BBT)
  5. The activity of the immune system
  6. The function of the hypothalamus (in the hypothalamus-pituitary-ovarian (HPO) axis)

The two hormones have very different, almost opposing effects:


  • Most estrogen is produced by large follicles maturing towards ovulation
  • Has a cooling effect on the body, and the higher the estrogen, the lower the BBT
  • Stimulates the functional layer of the endometrium to re-grow after the period
  • Increases fertile cervical mucus, which becomes thinner, stretchy or watery (see BBT)
  • Stimulates the cervix to open and become softer, shorter and higher in the vagina


  • All progesterone is produced by the corpus luteum (the ‘yellow body’), which develops from the dominant follicle that releases the egg
  • It has a heating effect on the body and raises the BBT by several tenths of a degree (however, the change in temperature stops when progesterone reaches 6 ng/ml)
  • Stimulates the functional layer to become spongy, sticky and blood-rich to encourage implantation
  • Reduces cervical mucus, and it becomes thick and impenetrable to sperm
  • Stimulates the cervix to close and become longer, harder and lower in the vagina
  • Prevents ovulation (second ovulation must be within 24 hours of the first one)

In normal cycles, the two hormones create two basal temperatures. The temperature is lower after the start of the period and rises after ovulation.

Progesterone in conception and pregnancy

The corpus luteum produces all the progesterone in the first two months of pregnancy. From this point, the placenta begins to produce progesterone, and by the end of the first trimester, all progesterone production is from the placenta. The levels of progesterone now increase dramatically, and the risk of miscarriage reduces.

Some women diagnosed with infertility, implantation failures and/or miscarriages have relatively low progesterone levels, and they may need progesterone supplementation to bring them up to safe levels. The stage of the pregnancy determines what a safe level is, and the thick line on the graph below shows the average values during pregnancy:

Progesterone affects the immune system and is believed to:

  1. Reduces inflammation that can cause scarring and damage to the placenta
  2. Block the white blood cells (lymphocytes) that can cause rejection of the placenta
  3. It prevents natural killer cells (NK) from releasing cytokines such as tumour necrosis factor (TNF) that can damage the placenta and endometrium
  4. It blocks lymphocytes from gathering in the placenta and damaging it
  5. Stimulate the placenta to increase hCG production (hCG and progesterone block the killing power of NK cells)
  6. Prevent prostaglandin production and the uterine contractions it stimulates
  7. Stimulate the cervix to produce a mucus plug that’s rich in antibodies to prevent germs and viruses from entering the womb

Progesterone supplementation

The problem with progesterone supplements is they have a very short “half-life” in the blood and can be excreted in the urine in minutes. The best ways to supplement are:

  1. Vaginal suppositories are effective at attaining and maintaining good levels in the blood
  2. Injections are considered the next best option
  3. Oral supplementation is the least effective way to take progesterone