What Is Progesterone?
Progesterone is a steroid hormone and belongs to a family called progestogens. During the female menstrual cycle, progesterone is secreted by a mass of cells called the corpus luteum. The corpus luteum forms in the ovary from the remnants of the ovarian follicle, which was home to a developing egg before it ruptured, releasing the egg in a process called ovulation. Once an egg has been fertilised, progesterone is produced by the placenta during pregnancy.
What Is The Role Of Progesterone?
Progesterone prepares the female body for pregnancy, just in case the egg, which has been released, is fertilised. If the egg isn’t fertilised, the corpus luteum will break down, progesterone levels will fall and a new menstrual cycle will begin.
If the egg is fertilised, progesterone is required to help sustain the pregnancy. So, some of the roles progesterone plays in pregnancy, include:
- Encouraging the growth of blood vessels to the lining of the womb (endometrium)
- Stimulate the secretion of nutrients from the endometrium to nourish the developing embryo
- Helps to thicken the lining of the uterus for the implantation of the fertilised egg
- Maintaining the endometrium throughout pregnancy
- Stimulates growth of breast tissue
- Prepares the body for labour by strengthening pelvic wall muscles
Progesterone levels fluctuate during the menstrual cycle, and will begin to decline as a woman transitions to menopause due to the ovaries becoming less responsive. Progesterone levels are low during the first phase of the menstrual cycled called the follicular phase and rise after ovulation known as the luteal phase. The below progesterone levels chart shows progesterone levels in women during the menstrual cycle:
Women who are post-menopausal have a progesterone reference range of <0.401 nmol/L.
The chart below shows progesterone level ranges during ovulation:
High Progesterone Levels
High progesterone levels are to be expected after ovulation and during pregnancy and do not cause any symptoms. However, sustained high levels of progesterone during the menstrual cycle and in the absence of pregnancy can be caused by two conditions, namely congenital adrenal hyperplasia and ovarian hyperstimulation syndrome.
Congenital Adrenal Hyperplasia
High levels of a particular type of progesterone called 17 OH progesterone is a symptom of a condition called congenital adrenal hyperplasia. Congenital adrenal hyperplasia is an inherited condition which is caused by the genes which code for enzymes needed to make steroid hormones in the adrenal glands being mutated. In Europe, the condition affects around 1 in 12,000 live births. In women, the condition can result in high progesterone levels which interfere with the normal ovulatory cycle and lead to impaired fertility.
Ovarian hyperstimulation syndrome (OHSS)
OHSS is a complication associated with fertility treatment, particularly in vitro fertilisation (IVF). It causes enlargement of the ovaries which is painful and may result in nausea and vomiting. Severe OHSS occurs in less than 1% of fertility treatment cases.
High levels of oestrogen, progesterone and human chorionic gonadotropin are thought to cause OHSS. The condition causes increased vascular permeability surrounding the ovaries and their blood vessel network, leading to symptoms such as:
- Low blood pressure
- Difficulty breathing
- Abdominal swelling/pain
Hormone Replacement Therapy (HRT)
For many menopausal women, the replacement of the female sex hormones, oestrogen and progesterone, in the form of HRT provide relief from the symptoms associated with this life stage.
Women who take HRT, containing the non-molecular identical continuous form of progesterone, will have increased levels of progesterone compared to those who do not take HRT. There are pros and cons to taking HRT, which need to be considered on an individual basis.
Low Progesterone Levels
Progesterone plays a vital role in female fertility and low levels can significantly reduce the chances of a female being able to fall pregnant. If a woman's body does not produce enough progesterone it can make it difficult to fall pregnant or sustain a pregnancy. If progesterone is not present in high enough levels, then the lining of the womb cannot be maintained, meaning a fertilised egg will not be able to implant itself in the womb. As a result, low progesterone levels prevent normal embryo growth.
Symptoms of low progesterone in women who are not pregnant include:
- Mood changes, anxiety and depression
- Headaches and/or migraines
- Heavy, irregular or no periods
In the UK, 12% of all gynaecology referrals are due to heavy menstrual bleeding. Heavy bleeding or menorrhagia, as it is clinically known, is defined as a total blood loss of 80ml or more in a menstrual period lasting over 7 days. Menorrhagia is associated with physical, emotional and social symptoms which can reduce the individual’s quality of life. In some cases, medical treatment may be required.
Low progesterone levels can also be a sign of conditions such as polycystic ovary syndrome.
Polycystic Ovary Syndrome
Women who have PCOS have been shown to have a lower progesterone concentration during the luteal phase of the menstrual cycle compared to women who do not have PCOS. One theory as to why this might be the case is that low progesterone is associated with high luteinising hormone or hypersecretion in PCOS.
PCOS is associated with an excess of androgens in females. For example, a high level of testosterone (hyperandrogenism) causing symptoms such as excess facial hair, persistent acne and high blood pressure. The hyperandrogenism could be caused by high levels of LH and it could be this which suppresses progesterone production.
Insulin may also be a contributing factor to low progesterone levels in PCOS.
How To Check Progesterone Levels
A progesterone blood test will help identify if you have ovulated by testing your levels of progesterone when the test is taken on day 21 of your menstrual cycle.
Progesterone is an important female hormone which plays a key role in fertility. A hormone imbalance can lead to low progesterone levels leading to a number of symptoms including female infertility.