Fertility simply refers to your ability to reproduce or have babies. Natural reproduction requires the production of an egg (ovulation) which depends on a complex cycle of hormonal changes in the body. It also requires the integrity of glands in the brain, which communicate with the egg-producing factory, the ovary.
Taking a closer look at hormone levels can give some useful information about fertility, however, it is important to understand their limitations.
The functions of the ovary are controlled by two hormones Luteinising hormone (LH) and Follicle Stimulating hormone (FSH). These hormones are produced by a gland in the brain called the Pituitary gland. If you are still having periods, LH and FSH should be done between day 2 and 5 of your cycle. The exception to this is If you are not having any menstrual periods.
Please note that FSH measurements are unreliable in those on combined oral contraceptives and high dose progestogens such as the contraceptive Implant and contraceptive Depo-Provera injection. It is also unreliable in those taking Hormone Replacement Therapy (HRT). FSH can be measured if you are taking the progesterone-only pill or using an intrauterine device such as the hormonal and non-hormonal coils.
The ovary produces the hormones oestradiol, progesterone, and testosterone. Progesterone levels rise after ovulation and reach a peak around day-21. A 21-day progesterone test can therefore provide a useful indication of whether you have ovulated or not. As the test indicates, it is carried out on day 21 0f your cycle or 7 days before the next menstrual period is due, if your cycles are longer than 28 days.
Testosterone levels can be higher than normal in conditions such as Polycystic Ovarian Syndrome. It is a condition that can result in periods occurring less frequently (called ‘oligomenorrhoea’) or not at all (called ‘amenorrhoea’). This can make it harder to get pregnant.
Sex Hormone Binding Globulin (SHBG) is a protein made in the liver. It binds hormones, mainly androgens (such as testosterone and dihydrotestosterone) and oestrogens. SHBG is more tightly bound to testosterone and this is the hormone of particular focus when we request a SHBG test. If the SHBG levels are low (as can occur in conditions such as Obesity, Type 2 Diabetes, an under-active thyroid and excess growth hormone called Acromegaly), there is an increase in the level of free testosterone circulating in the blood. More free testosterone, means more gets into tissues which can lead to changes in the body that can affect the way the ovaries work. Conversely, an increase in the level of SHBG (as can occur in conditions such as an over-active thyroid, and liver cirrhosis), can cause a fall in the level of free testosterone. This can also affect the way the ovaries work.
Anti-Mullerian hormone (AMH) is a hormone produced by the cells that line the egg follicles. As we get older, the number of egg follicles declines and so does the level of AMH. We could therefore consider the AMH as a marker of ‘ovarian aging’. It is used widely in the preparation for In vitro fertilisation (IVF) as it can be a useful tool to predict ovarian response. It cannot as yet be used in clinical practice to predict the age of menopause as further clinical research is required. The most reliable measure of egg quantity or ‘ovarian reserve’ is an ‘antral follicle count’. This is a method of counting the number of egg follicles under direct visualisation using ultrasound. The higher the count, the higher the ovarian reserve.
Prolactin is a hormone produced by the pituitary gland. It maintains milk-production from ‘mammary glands’ inside the breasts during breast-feeding. Raised levels of prolactin can occur even if you are not breast-feeding. Stress is an important physiological cause of a raised prolactin level. Other causes include medications, an underactive thyroid gland, and tumours of the pituitary gland. High levels of prolactin can disrupt ovulation, resulting in infrequent or irregular periods.
Untreated Thyroid disorders such as hyperthyroidism (an ‘over-active thyroid’) or hypothyroidism (an ‘underactive thyroid’) can make ovulation more challenging and so can negatively impact fertility. It is important to remember that if you are taking levothyroxine for an underactive thyroid, your requirement will increase during pregnancy. Therefore, you need to increase your dose of levothyroxine once you have a positive pregnancy test. Speak to your doctor if you are taking levothyroxine and have a positive pregnancy test.
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