An anovulatory cycle is a menstrual cycle during which the ovaries do not release an oocyte. Therefore, ovulation does not take place. However, a woman who does not ovulate at each menstrual cycle is not necessarily going through menopause. Chronic anovulation is a common cause of infertility.
In addition to the alteration of menstrual periods and infertility, chronic anovulation can cause or exacerbate other long term problems, such as hyperandrogenism or osteopenia. It plays a central role in the multiple imbalances and dysfunctions of polycystic ovary syndrome.
During the first two years after menarche 50% of the menstrual cycles could be anovulatories.
It is in fact possible to restore ovulation using appropriate medication, and ovulation is successfully restored in approximately 90% of cases. The first step is the diagnosis of anovulation. The identification of anovulation is not easy; contrary to what is commonly believed, women undergoing anovulation still have (more or less) regular periods. In general, patients only notice that there is a problem once they have started trying to conceive.
Temperature charting is a useful way of providing early clues about anovulation, and can help gynaecologists in their diagnosis.
The World Health Organization criteria for classification of anovulation include the determination of oligomenorrea (menstrual cycle >35 days) or amenorrea (menstrual cycle > 6 months) in combination with concentration of prolactin, follicle stimulating hormone (FSH) and estradiol (E2). The patients are classified as WHO1 (15%) - hypo-gonadotropic, hypo-estrogenic, WHO2 (80%) - normo-gonadotropic, normo-estrogenic, and WHO3 (5%) - hyper-gonadotropic, hypo-estrogenic. The vast majority of anovulation patients belong to the WHO2 group and demonstrate very heterogeneous symptoms ranging from anovulation, obesity, biochemical or clinical hyperandrogenism and insulin resistance.
Hormonal or chemical imbalance
This is the most common cause of anovulation and is thought to account for about 70% of all cases.
- About half the women with hormonal imbalances do not produce enough follicles to ensure the development of an ovule. This could be caused by poor hormonal secretions from the pituitary gland or the hypothalamus.
- The pituitary gland controls most other hormonal glands in the human body. Therefore, any pituitary malfunctioning affects other glands under its influence, which includes ovaries. This occurs in around 10% of the cases. Mammary glands are also controlled by the pituitary gland, which can thus also affect lactation.
- The hypothalamus controls the pituitary gland. In 10% of the cases, alterations in the chemical signals from the hypothalamus can easily seriously affect the ovaries.
- There are other hormonal anomalies with no direct link to the ones mentioned above that can affect ovulation. For instance, women with hyper or hypo-thyrodism sometimes have ovulation problems. Thyroid dysfunction can halt ovulation by upsetting the balance of the body’s natural reproductive hormones. Polycystic ovary syndrome (also known as Stein-Leventhal syndrome) and hyperprolactinemia can also cause anovulatory cycles through hormonal imbalances.
This accounts for around 10-15% of all cases of anovulation.
- The ovaries can stop working in about 5% of cases. This may be because the ovaries do not contain eggs. However, a complete blockage of the ovaries is rarely a cause of infertility. Blocked ovaries can start functioning again without a clear medical explanation.
- A significant emotional shock can temporarily affect the functioning of the brain and can lead to dysfunction of the hypothalamus. However, this is not as common as people might think.
- In some cases, the egg may have matured properly, but the follicle may have failed to burst (or the follicle may have burst without releasing the egg). This is called luteinised unruptured follicle syndrome (LUFS). Physical damage to the ovaries, or ovaries with multiple cysts, may affect their ability to function. This is called ovarian dystrophy. Patients who are suffering from Stein-Leventhal syndrome (also referred to as polycystic ovary syndrome, or PCOS) can also suffer from anovulation. Up to 90% of cases of anovulation are caused by PCOS; this syndrome is usually hereditary.
- Weight loss or anorexia can also cause hormonal imbalance, leading to irregular ovulation (dysovulation). It is possible that this mechanism evolved to protect the mother’s health. A pregnancy where the mother is weak could pose a risk to the baby’s and mother’s health. On the other hand, excess weight can also create ovarian dysfunctions. Dr Barbieri of Harvard Medical School has indicated that cases of anovulation are quite frequent in women with a BMI (body mass index) over 27 kg/m2. Unfortunately, not only does excess weight have a negative impact on ovulation itself, but also on treatment efficacy and outcomes of ART (assisted reproductive technique).
Signs and symptoms
Anovulation is usually associated with specific symptoms. However, it is important to note that they are not necessarily all displayed simultaneously.
- Amenorrhea (absence of menstruation) occurs in about 20% of women with ovulatory dysfunction.
- Infrequent and light menstruations occur in about 40% of women with ovulatory dysfunction.
- Irregular menstruation, where five or more menstrual cycles a year are five or more days shorter or longer than the length of the average cycle.
- Absence of mastodynia (breast pain or tenderness) occurs in about 20% of women with ovulatory problems.
- Increased body mass and facial hair (this is relatively easy to treat, and is often associated with PCOS, or polycystic ovary syndrome).
Fertility awareness and LH measurement
Symptoms-based methods of fertility awareness may be used to detect ovulation or to determine that cycles are anovulatory. Charting of the menstrual cycle may be done by hand, or with the aid of various fertility monitors. Records of one of the primary fertility awareness signs—basal body temperature—can detect ovulation by identifying the shift in temperature which takes place after ovulation. It is said to be the most reliable way of confirming whether ovulation has occurred.
Women may also use ovulation predictor kits (OPKs) which detect the increase in luteinizing hormone (LH) levels that usually indicates imminent ovulation. For some women, these devices do not detect the LH surge, or high levels of LH are a poor predictor of ovulation; this is particularly common in women with PCOS. In such cases, OPKs and those fertility monitors which are based on LH may show false results, with an increased number of false positives or false negatives. Dr Freundl from the University of Heidelberg suggests that tests which use LH as a reference often lack sensitivity and specificity.
Treatments available to induce ovulation are usually quite efficient. The European Society of Human Reproduction and Embryology (ESHRE) notes that the aim of ovulation induction should be mono-ovulation and not over-stimulation of the ovaries. The risks associated with multiple pregnancies are much higher than singleton pregnancy; incidences of perinatal death are seven times higher in triplet births and five times higher in twin births than the risks associated with a singleton pregnancy. It is therefore important to adapt the treatment to each individual patient.
- The medication which is most commonly used to treat anovulation is clomifene citrate (or clomid). It is relatively easy and convenient to use. Clomifene appears to inhibit estrogen receptors in hypothalamus, thereby inhibiting negative feedback of estrogen on gonadotropin production. It may also result in direct stimulation of the hypothalamic-pituitary axis. It also has an effect on cervical mucus quality and uterine mucosa, which might affect sperm penetration and survival, hence its early administration during the menstrual cycle. Clomifene citrate is a very efficient ovulation inductor, and has a success rate of 67%. Nevertheless, it only has a 37% success rate in inducing pregnancy. This difference may be due to the anti-estrogenic effect which clomifene citrate has on the endometrium, cervical mucus, uterine blood flow, as well as the resulting decrease in the motility of the fallopian tubes and the maturation of the oocytes.
- Another anti-estrogenic molecule called tamoxifen is often used in the prevention and treatment of breast cancer. It can therefore also be used to treat patients that have a reaction to clomifene citrate.
- Human chorionic gonadotropin (hCG) is a molecule which is structurally similar to luteinizing hormone (LH). LH is secreted by the pituitary just before ovulation occurs, whereas hCG is released during pregnancy. On its own, hCG is not very effective in inducing ovulation, but when combined with clomifene citrate, it is much more effective. The results associated with this method have been described as "quite encouraging". HCG should only be administered at certain points in the cycle, around the time of ovulation, and only if the infertility diagnostic has indicated that the problem is related to the release of the egg.
- Human menopausal gonadotropin (hMG) is a very powerful treatment for infertility. It consists of a combination of LH and FSH. From menopause onwards, the body starts secreting LH and FSH in large quantities due to the slowing down of the ovarian function. This excess of hormones is not used by the body and is expelled in the urine. HMG is therefore collected from the urine of menopausal women. The urine then undergoes purification and a chemical treatment. The resulting hMG induces the stimulation of several ovarian follicles. This increases the risk of producing several oocytes during the same cycle, and thus the risk of multiple pregnancies.
- Follicle-stimulating hormone (FSH or recombinant FSH) is now used as a replacement for hMG. Although hMG is a combination of FSH and LH, FSH is the only active component that has an effect on ovulation. However, until recently, it was not possible to produce pure FSH. FSH is now administered in a similar way as hMG, at a specific point during the cycle, and it requires medical monitoring. It is therefore important to fully understand a woman’s cycle, and to be able to accurately anticipate menstruation and ovulation dates. FSH is also sometimes useful for women who are suffering from PCOS.
- The gonadotropin-releasing hormone (GnRH) pump is used to release doses of GnRH in a pulsatile fashion. This hormone is synthesised by the hypothalamus and induces the secretion of LH and FSH by the pituitary. GnRH must be delivered in a pulsatile fashion to imitate the random secretion of the hypothalamus in order to fool the pituitary into secreting LH and FSH. The GnRH pump is the size of a cigarette box and has a small catheter. Unlike other treatments, using the GnRH pump doesn’t usually lead to multiple pregnancies. Dr. Filicori from the University of Bologna suggests that this might be because gonadotrophins are absent when the treatment is initiated, and therefore the hormones released by the pituitary (LH and FSH) can still take part in the retro-control of gonadotrophin secretion, mimicking the natural cycle. This treatment can also be used for underweight and/or anorexic patients; it has also been used in certain cases of hyperprolactimenia.
- Bromocriptine acts in a completely different manner to the other treatments mentioned above. It does not induce ovulation, but reduces the production of prolactin by the pituitary. Bromocriptine is only prescribed in cases of overproduction of prolactin (hyperprolactinemia).
- Corticosteroids (usually found in anti-inflammatory drugs) can be used to treat anovulation if it is caused by an overproduction of male hormones by the adrenal glands. Corticosteroids are usually used to reduce the production of testosterone.
- Several studies indicate that in some cases, a simple change in lifestyle could help patients suffering from anovulation. Consulting a nutritionist, for example, could help a young women suffering from anorexia to put on some weight, which might restart her menstrual cycle. Conversely, a young overweight woman who manages to lose weight could also relieve the problem of anovulation (losing just 5% of body mass could be enough to restart ovulation). However, it is widely acknowledged by doctors that it is usually very difficult for PCOS patients to lose weight.
Previously, metformin was recommended as treatment for anovulation in polycystic ovary syndrome, but in the largest trial to date, comparing clomiphene with metformin, clomiphene was more effective than metformin alone. Following this study, the ESHRE/ASRM-sponsored Consensus workshop do not recommend metformin for ovulation stimulation. Subsequent randomized studies have confirmed the lack of evidence for adding metformin to clomiphene.
For most women, alteration of menstrual periods is the principal indication of chronic anovulation. Ovulatory menstrual periods tend to be regular and predictable in terms of cycle length, duration and heaviness of bleeding, and other symptoms. Ovulatory periods are often accompanied by midcycle symptoms such as mittelschmerz or premenstrual symptoms. In contrast, anovulation usually manifests itself as irregularity of menstrual periods, that is, unpredictable variability of intervals, duration, or bleeding. Anovulation can also cause cessation of periods (secondary amenorrhea) or excessive bleeding (dysfunctional uterine bleeding). Mittelschmerz and premenstrual symptoms tend to be absent or reduced when a woman is anovulatory.
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