Progesterone is a naturally occurring steroid hormone central to the female body, particularly concerning the menstrual cycle and conception. It is primarily produced by the ovaries, specifically by the corpus luteum, the structure remaining after an egg is released. Maintaining healthy levels is necessary for preparing the body for potential pregnancy and influencing broader systemic health. A decline in progesterone can disrupt these processes, leading to noticeable physical and emotional changes.
The Role of Progesterone in the Body
Progesterone’s main reproductive function is preparing the uterine lining (endometrium) for the potential implantation of a fertilized egg. Following ovulation, the corpus luteum releases progesterone, causing the endometrium to thicken and become enriched with blood vessels and nutrients. If conception occurs, the hormone continues production to support early pregnancy and prevent uterine contractions.
Beyond reproduction, progesterone influences several other bodily systems. It has a calming effect on the central nervous system, contributing to better sleep and mood stability. The hormone also plays a role in bone health by stimulating osteoblasts, which build new bone tissue. Furthermore, it helps regulate the effects of estrogen, maintaining a healthy hormonal balance.
Recognizing the Common Symptoms
The most immediate signs of low progesterone often involve changes in the menstrual cycle. Insufficient production may be indicated by a shorter-than-average luteal phase (the time between ovulation and the start of a period). Spotting or light bleeding in the days leading up to menstruation is another common sign of a weak or declining corpus luteum.
Low levels can also interfere with maintaining a pregnancy. Difficulty conceiving or recurrent early miscarriages are frequently associated with insufficient progesterone to sustain the uterine lining. The hormone is needed to create a stable environment for the implanted embryo; its absence can lead to the breakdown of the endometrium.
Systemic and mood-related symptoms are highly prevalent, often worsening during the premenstrual phase. Many people report increased anxiety, irritability, or general mood swings. Because progesterone supports the brain’s calming GABA receptors, its decline can also lead to sleep disruption and insomnia, especially in the latter half of the cycle.
Medical Testing and Diagnosis
A definitive diagnosis of low progesterone requires medical testing performed by a healthcare provider. The standard method is a simple blood draw, which assesses the amount of the hormone circulating in the bloodstream. This test is commonly referred to as a Progesterone Serum Concentration test or a Day 21 Progesterone test.
The timing of the blood test is important because progesterone levels fluctuate dramatically throughout the menstrual cycle. The test must be scheduled during the mid-luteal phase, when levels are expected to peak after ovulation. For a person with a regular 28-day cycle, this usually falls around day 21.
For individuals with irregular cycles, timing is adjusted to approximately seven days before the expected start of menstruation to capture peak production. A serum progesterone level of 5 nanograms per milliliter (ng/mL) or higher is considered evidence that ovulation has successfully occurred. Consistently low levels, especially below this threshold, suggest insufficient progesterone production or a failure to ovulate.
Underlying Causes and Contributing Factors
Low progesterone is often a direct result of anovulation, the absence of egg release from the ovary during a cycle. When an egg is not released, the corpus luteum—the structure that produces progesterone—never forms correctly. Conditions that interfere with regular ovulation are primary causes of low progesterone.
Thyroid dysfunction, such as hypothyroidism, and Polycystic Ovary Syndrome (PCOS) are common medical conditions that impair the hormonal signals needed for proper ovulation. Lifestyle factors also play a role, as chronic stress elevates cortisol, which interferes with hormone production.
Excessive exercise or inadequate nutrition can signal that it is not a safe time for reproduction, suppressing ovulation and lowering progesterone. The natural decline of ovarian function during perimenopause and menopause is another common cause of decreasing levels.
Next Steps After Diagnosis
Once a healthcare provider confirms low progesterone, the next step involves discussing management strategies tailored to the individual’s goals. For those trying to conceive, treatment often involves progesterone supplementation. This can be administered through oral capsules, vaginal suppositories, or topical creams and gels. These supplements support the uterine lining and help sustain an early pregnancy.
Management also includes addressing any underlying medical or lifestyle factors. Correcting conditions like thyroid dysfunction or hyperprolactinemia is the first approach to restoring normal hormone balance. Simple lifestyle adjustments, such as stress management, adequate sleep, and a healthy diet, can also support the body’s natural progesterone production.