Progesterone

The range depends entirely on the timing: below about 5 nmol/L in the first half of the cycle, in men and after the menopause; roughly 5 to 86 in the second half, and labs often add a comment that a mid-luteal (day 21) value above about 30 nmol/L is what is seen after ovulation.

Progesterone is the hormone made by the ovary after an egg has been released, from the structure left behind called the corpus luteum. It prepares the womb lining for a pregnancy and keeps it in place. Because it rises only after ovulation, the level in the second half of the cycle shows whether ovulation has happened that month.

It is mostly requested in fertility assessment to check that ovulation is occurring, taken about seven days before the next period is due (day 21 of a 28-day cycle). It is also used in early pregnancy clinics and to monitor some fertility treatments.

• The second half of the menstrual cycle, after ovulation
• Pregnancy, where it rises steadily
• Progesterone-containing medicines and some fertility treatments
• Rarely, ovarian cysts or adrenal conditions

• The first half of the cycle, when it is naturally low
• Cycles in which no egg was released, which happen occasionally in everyone
• The menopause
• A sample taken too early or too late in the cycle to catch the peak
• Hormonal contraception that stops ovulation

• A low value simply means no egg was released that cycle or the sample was taken on the wrong day; most people have the occasional cycle like this
• Cycles longer or shorter than 28 days move the right sampling day
• Assays differ at low levels

Timing is everything: the sample is taken about seven days before the next period is expected, which is day 21 only in a 28-day cycle. Labs ask for the cycle day and cycle length. No fasting needed.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.