Progesterone explained

The job description

Progesterone has several functions that differ from oestrogen. Knowing them helps you understand why the balance between the two hormones matters so much.

In the menstrual cycle

Progesterone is produced after ovulation by the corpus luteum, the structure left behind by the released egg. It prepares the uterine lining for a potential pregnancy by making it receptive to embryo implantation. If no pregnancy occurs, progesterone production stops, levels fall and the uterine lining sheds as a period. The whole second half of the cycle is essentially the progesterone phase.

In pregnancy

Progesterone is essential for maintaining pregnancy. Levels rise dramatically through the first trimester, then plateau at high levels for the rest of pregnancy. The placenta takes over progesterone production from the corpus luteum after the first trimester. Adequate progesterone supports the uterus and prevents contractions that would end the pregnancy.

Beyond reproduction

Progesterone affects mood, sleep, body temperature, breast tissue and several other systems. It has calming effects for some women but can produce low mood and irritability in others, depending on individual sensitivity. Progesterone influences the brain through GABA receptors, which is part of why it can have sedating effects. The mood effects vary widely between women.

The temperature effect

Progesterone raises basal body temperature by about 0.3 to 0.5 degrees Celsius after ovulation. The temperature rise is one way to identify ovulation through basal body temperature charting. The slightly higher temperature persists through the luteal phase until just before the next period, when it falls again.

Production patterns

Progesterone production depends on ovulation. Knowing when and how much progesterone is produced helps make sense of various symptoms.

Only after ovulation

Progesterone is produced almost entirely after ovulation by the corpus luteum. The follicular phase before ovulation has very low progesterone. In cycles where ovulation does not happen, progesterone is not produced. This matters because the absence of ovulation often leads to oestrogen dominance, which contributes to heavy periods and other symptoms.

The luteal pattern

Progesterone rises rapidly after ovulation, peaking about a week later in the middle of the luteal phase. It then falls in the days before the next period if no pregnancy has occurred. This pattern produces the characteristic temperature rise and fall. The cyclical mood and physical symptoms many women notice are also part of it in the late luteal phase.

In pregnancy

If pregnancy occurs, the corpus luteum continues producing progesterone for the first 7 to 10 weeks, supported by HCG (the hormone detected by pregnancy tests). The placenta takes over progesterone production after this. Levels rise to far higher than anything in a normal cycle and stay high until birth.

After menopause

Progesterone production essentially stops at menopause because ovulation has stopped. Women on HRT who still have a uterus need progesterone alongside oestrogen because unopposed oestrogen thickens the uterine lining and raises cancer risk. Women who have had a hysterectomy can take oestrogen only HRT.

Progesterone problems

Several specific problems can arise from progesterone production or sensitivity. Recognising the patterns helps target treatment.

Short luteal phase

A luteal phase shorter than 10 days suggests inadequate progesterone production. This is called luteal phase defect and can affect fertility because the uterine lining does not have time to develop properly for implantation. Diagnosis requires tracking cycles. Treatment may include progesterone supplementation, particularly in women trying to conceive. Speak to your GP.

Anovulatory cycles

Cycles where ovulation does not happen produce no progesterone. The result is cycles dominated by oestrogen without the balancing effect of progesterone. This pattern contributes to heavy periods, breast tenderness and other symptoms. Anovulatory cycles are common in adolescence, perimenopause and in women with PCOS or other conditions that disrupt ovulation.

PMS and PMDD

The dropping progesterone (alongside oestrogen) in the late luteal phase contributes to PMS and PMDD symptoms. Some women are particularly sensitive to the hormonal changes. Treatment can include hormonal manipulation to smooth the changes, antidepressants that work on serotonin and other approaches. Speak to your GP.

Pregnancy concerns

Low progesterone in early pregnancy was historically linked to miscarriage risk, though the relationship is more complicated than simple cause and effect. Progesterone supplementation is sometimes used in early pregnancy in specific situations, particularly with previous miscarriages. The evidence for routine supplementation is limited. Speak to your obstetric team for individual advice.

Progesterone as medicine

Progesterone can be supplemented for various reasons. Different forms and routes of administration suit different situations.

Forms of progesterone

Body identical progesterone (micronised progesterone, brand name Utrogestan in the UK) is the same molecule as the body produces. Synthetic progestogens (different chemicals with progesterone like effects) include those used in many contraceptive pills and older HRT preparations. The body identical form is increasingly preferred for HRT and other uses.

In HRT

Women on HRT who still have a uterus need progesterone alongside oestrogen to protect the uterine lining. Body identical progesterone taken orally at night is a common approach. The hormonal IUD provides progesterone locally to the uterus and is another option. Vaginal progesterone is also available. Speak to your GP about the right approach for you.

For PMS and cycles

Progesterone treatment is sometimes used for PMS and cycle problems, though the evidence is mixed. The combined contraceptive pill, which contains synthetic progestogen, helps many women through stabilising hormones across the cycle. Pure progesterone treatment for PMS has had limited evidence of benefit beyond placebo.

In fertility treatment

Progesterone supplementation is commonly used after assisted reproduction techniques like IVF, often as vaginal pessaries. The aim is to support implantation and early pregnancy. The evidence supports this use in assisted reproduction even though the evidence for progesterone use in spontaneous pregnancies is limited.

More on female health

For the partner hormone, our Oestrogen: What It Does and Why It Matters covers the other main female hormone. The Four Hormonal Phases of the Menstrual Cycle covers how progesterone fits into the cycle. And The Key Hormones That Drive Female Health covers the full picture of female hormones.