Progesterone

Progesterone is a female sex hormone secreted after ovulation by the corpus luteum in the ovary. Its level in the second half of the cycle indirectly indicates whether ovulation occurred, so testing is most often performed in infertility and irregular-cycle investigations and, on a doctor’s advice, in early pregnancy.

Who is this test for

• women having difficulty conceiving, to check ovulation;
• women with irregular or absent periods, alongside other hormones;
• women receiving infertility treatment, to monitor ovulation as instructed by a gynaecologist;
• women in early pregnancy when a gynaecologist assesses its progress, alongside beta-hCG and ultrasound.

What progesterone is and what it shows

After ovulation, the follicle that released the egg becomes the corpus luteum, which secretes progesterone. It prepares the uterine lining (endometrium) for implantation of a fertilised egg. If pregnancy does not occur, the corpus luteum degenerates, progesterone falls and menstruation begins. In pregnancy, the corpus luteum initially secretes progesterone, then the placenta takes over. Small amounts are also produced by the adrenal glands and, in men, the testes.

Because progesterone rises markedly only after ovulation, a high value in the middle of the cycle’s second half (luteal phase) shows that ovulation probably occurred. This is indirect confirmation: the result says nothing about egg quality, fallopian tube patency or whether pregnancy will occur.

Progesterone is not the same as 17-hydroxyprogesterone, a test used in investigations of adrenal disorders and excessive hair growth.

Which cycle day to test progesterone

Blood is sampled approximately 7 days before the expected period, when progesterone is highest. In a 28-day cycle, this is day 21–23, counting the first menstrual day as day 1. In longer cycles, testing is later, for example in a 35-day cycle around day 28.

With irregular cycles, choosing the right day is difficult, so a doctor may recommend weekly repeat testing until the next period. Record the sampling date and when menstruation began, because interpretation depends on them.

Save with a panel

Test Progesterone is also included in these panels.

Perimenopause assessment panelFSH, LH, oestradiol, progesterone, TSHPrice of individual tests: 82.00€74.00€Details ›Early menopause assessment panelFSH, LH, oestradiol, progesterone, prolactin, TSHPrice of individual tests: 100.00€90.00€Details ›Hormonal status panel – womenTSH, fT3, fT4, cortisol and oestrogen, progesterone and 3113.00€Details ›

All panels including Progesterone (5) ›

Preparation and sample

Progesterone is measured in venous blood, and fasting is not required. If you use hormonal contraception, testing to check ovulation is not useful because pills prevent ovulation. Progesterone preparations and ovulation-stimulating medicines change results, so tell your doctor if you take them. If you take biotin (e.g. hair and nail supplements), mention this at blood collection.

How results are interpreted

Reference values depend on cycle phase, pregnancy and method and are printed on the report. A gynaecologist interprets them alongside cycle day, cycle length and other hormones.

• High progesterone in the second half of the cycle is expected and suggests ovulation occurred during that cycle.
• Low progesterone most often means blood was not taken at the right time, for example because ovulation occurred later than expected, or that the cycle had no ovulation. An occasional cycle without ovulation also occurs in healthy women, so testing is often repeated. If ovulation is absent for several consecutive cycles, the cause may be polycystic ovary syndrome, abnormal thyroid function (checked through TSH), high prolactin, a major weight change or perimenopause.
• During pregnancy progesterone rises. A single result does not show pregnancy progress; a gynaecologist interprets it alongside beta-hCG and ultrasound.

Alongside progesterone, fertility investigations usually include early-cycle hormones, FSH, LH and estradiol, and to assess ovarian reserve, AMH.

How to arrange testing

You can come for blood collection without an appointment or referral at one of our branches throughout Croatia (listed on the Contactpage). Prices for all tests and panels are listed in the service price list. Other hormones important for fertility are included in the Fertility Investigation Panel, while progesterone is sampled separately in the second half of the cycle.

Frequently asked questions

On which cycle day is progesterone tested?

With a 28-day cycle, on day 21–23, approximately 7 days before the expected period. With longer or shorter cycles, the day changes; determine it according to your cycle length or medical advice.

What does low progesterone on day 21 mean?

If your cycle is longer than 28 days, ovulation may have occurred later and blood was taken too early. If timing was correct, a low result suggests a cycle without ovulation. One such result is not a cause for concern; a doctor usually recommends repeating it in the next cycle.

Can progesterone confirm pregnancy?

No. Pregnancy is confirmed through blood or urine beta-hCG and ultrasound; a gynaecologist sometimes uses progesterone as additional information in early pregnancy.

Can progesterone be tested while I take contraceptive pills?

Yes, but results will not show ovulation because pills prevent it. If checking ovulation is the aim, discuss stopping contraception and test timing with your gynaecologist.