- Ovarian reserve is a term that is used to determine the capacity of the ovary to provide egg cells that are capable of fertilisation resulting in a healthy and successful pregnancy.
- The ovarian reserve is at maximum value in sixth-month-old embryos.
- The ovary is generally thought of as an egg bank from which the woman draws during her reproductive life.
Infertility is defined as the inability for a couple to conceive despite regular unprotected sexual intercourse. Around 1 in 6 couples in the UK may have difficulty conceiving, which is approximately around 3.5 million people. Almost 84% of couples that have regular unprotected sex (on average 2 or 3 times a week) will be able to conceive naturally within a year and 92% of couples will conceive naturally within 2 years of regular unprotected sex.
Couples who have been trying to conceive for more than 3 years unsuccessfully have 25% or less chance of falling pregnant naturally within the next year.
It is therefore advisable to seek medical advice if you have not conceived after a year of trying. Your doctor will get a detailed medical history from you and run investigations to try and identify the cause of your fertility problem before suggesting treatments that could help.
What is the most important factor for a successful pregnancy?
The most important factor for a successful pregnancy resulting in a successful birth is the quality of eggs. The best measure of egg quality is usually the age of the woman.
Most women are aware and conscious of their ticking ‘biological clocks’. However, as they have better opportunities in education nowadays they choose to have their first children at a later stage. The vast majority of women will have no difficulties conceiving and having babies when ready to do so. However, the older women get, the more difficult it may be to get conceive.
Many couples will be able to conceive naturally following medical or surgical treatment and some will require extra support to conceive and usually will need an in vitro fertilisation (IVF) with their eggs or with donor eggs.
Are women born with a number of eggs or do they continue to produce more during their life?
Women are born with a set number of eggs which they use for the rest of their reproductive life. They do not produce any new eggs over the years. The average female foetus has around 5 million eggs in their ovaries by 20 weeks of pregnancy. During development within its mother’s womb, the foetus will lose more than half of the eggs, with the average baby girl having around 2 million eggs at birth.
During growth and development in childhood, more than half of the eggs will be lost, and by puberty (teenage years), the egg reserve will drop to 0.5 to 1 million eggs. These immature eggs are all dormant(asleep). However, at the beginning of each menstrual cycle (monthly period), a small number of immature eggs will be recruited (woken up) from this egg pool. The recruited eggs can be seen as tiny fluid-filled sacs in the ovaries with an ultrasound scan. These are known as antral follicles and on average there would be 5 – 10 in each ovary.
How does ovulation happen?
The pituitary gland in the brain produces a hormone known as follicle stimulating hormone (FSH). FSH does exactly what the name suggests, stimulating one out of all the follicles exist in the ovary that month. The selected and stimulated follicle will develop and pop in mid-cycle, releasing a mature egg. This is process is known as ovulation. The rest of the follicles will eventually die off over the following weeks, and the same process will be repeated in each cycle. This is why the pool of eggs a woman holds is gradually reduced over time.
Menopause kicks in when around 1,000 immature eggs are left in the ovaries.
Only 400-450 eggs out of the pool of millions get to ovulate during a woman’s reproductive life. The rest die off. Their better quality eggs are usually released when a woman is at a younger age and this is why is easier to get pregnant. As women get older, the quantity and quality of eggs reduce, which explains why it takes longer to get pregnant and the reason miscarriage rates increase due to chromosomally abnormal embryos. The rate of chromosomal abnormalities such as Down’s syndrome also increases.
How can the ovarian reserve be measured?
The follicles within an ovary produce a hormone called Anti- Müllerian Hormone (AMH). The more eggs a woman has in reserve, the more antral follicles will be recruited and the higher the AMH level will be, and vice versa.
Between three to four in ten women will be born with an above average egg reserve and tend to recruit more than 12 antral follicles in each ovary. For this reason, their AMH levels will be very high. The ovaries will be larger than average. These are known as polycystic ovaries (PCO). Most women with PCO have no fertility problems and tend to go through the menopause later than average. However, some women with PCO may not release an egg every month (resulting in long menstrual cycles or no periods at all) or have higher than average testosterone levels. These testosterone levels can be identified in blood tests or could cause acne or excessive body hair. This condition is known as a polycystic ovarian syndrome (PCOS).
It is important to clarify that the AMH levels determine the quantity, but not the quality of the eggs.
AMH test helps you to plan ahead
AMH testing can benefit any woman or couple, regardless of age:
– younger women who may not be ready to start a family now and would like to be reassured that time is on their side
-women whose mothers have had early menopause will be to determine their risk of early menopause
– women of advancing maternal age (over 35 years of age), or when circumstances dictate.
Please note that the AMH test is a snapshot of the female egg reserve and is not a guarantee for the future. Retesting should be carried out in individuals who are looking to delay the onset of motherhood following an AMH result.
More information can be found on the Herts & Essex Fertility Centre website.