Progesterone

What is progesterone?

Progesterone is a hormone that is naturally produced in the body. In women, the corpus luteum, the residual structure of the follicle after ovulation, produces the largest amount. The adrenal cortex contributes to a smaller extent to production. Progesterone is also present in men, albeit in significantly lower concentrations.

The hormone has multiple functions. The most well-known is preparing the uterine lining for the possible implantation of a fertilized egg. Progesterone thickens this lining and reduces uterine contractions. If fertilization does not occur, progesterone production drops and menstruation begins. If pregnancy does occur, progesterone inhibits further ovulation and helps prevent a miscarriage.

In addition to reproductive function, progesterone also influences sleep, mood, and skin health. It is therefore a hormone with a broader impact on daily well-being than is often thought.

Why is progesterone measured?

Doctors measure progesterone for several reasons. The most common is to determine whether ovulation has occurred. After ovulation, the progesterone level rises and remains elevated during the second half of the cycle, the luteal phase. A measurement within this window provides reliable information about whether and when ovulation has occurred. This is useful for those wishing to conceive or for investigating anovulation, the absence of ovulation.

During pregnancy, progesterone continues to rise. Regular measurements help assess whether the placenta is producing sufficient hormone to support the pregnancy. A value that is too low in early pregnancy may indicate an increased risk of miscarriage or an ectopic pregnancy.

Progesterone is also measured in cases of hormonal disorders such as polycystic ovary syndrome (PCOS), endometriosis, or unexplained fertility problems. In combination with other hormones, such as estradiol, it provides a more complete picture of the hormonal balance and can guide further investigation or treatment.

What do abnormal values ​​mean?

Progesterone levels that are too low

A low progesterone level can have several causes. In the case of anovulation, little to no progesterone is produced because the corpus luteum does not form without ovulation. This leads to a chronically low level throughout the entire cycle.

Another cause is luteal phase insufficiency, where the luteal phase is too short or produces insufficient progesterone. This can make implantation difficult or contribute to an early miscarriage. In women with PCOS, progesterone levels are often structurally low due to irregular or absent ovulation.

Symptoms associated with low progesterone include irregular or painful menstruation, mood swings, premenstrual symptoms, and difficulty conceiving. These symptoms are not exclusive to this hormone, but they can be a reason to have the level determined.

High progesterone levels

An elevated progesterone level is fully expected and even desired during a normal pregnancy. Outside of pregnancy, high levels may indicate a corpus luteum cyst, a benign sac on the ovary that develops after ovulation and continues to produce progesterone.

An estrogen deficiency can prompt the body to produce compensatory progesterone, which also leads to elevated levels. In rarer cases, a tumor of the adrenal cortex may be the cause. Associated symptoms may include: irregular menstruation, sensitive or enlarged breasts, acne, weight gain, and fatigue.

Reference values ​​and when to measure?

Progesterone levels are expressed in nmol/L and vary significantly by phase of the cycle and stage of life. The following guideline values ​​are generally used:

• Follicular phase (first half of cycle): lower than 4.5 nmol/L

• Luteal phase (second half of cycle): 11 to 81 nmol/L

• After menopause: lower than 2.3 nmol/L

• Men: 0.9 to 3.9 nmol/L

The correct timing of the measurement is crucial. A measurement during the luteal phase, approximately seven days before the expected menstruation, provides the most relevant information regarding whether ovulation has occurred. Assessing a result without knowing when in the cycle the measurement was taken can easily lead to incorrect conclusions.

Consider a progesterone measurement if you are actively trying to conceive, suspect irregular ovulation, experience persistent premenstrual symptoms, or if a doctor recommends additional hormonal testing. Even a single measurement provides valuable information, but the doctor will always view the result in conjunction with other hormone levels and the clinical situation.