A woman's fertility depends on two important factors:

How many eggs remain (egg quantity) and how healthy those eggs are (egg quality).

Although these are related, they are not the same thing.

As women age:

• the number of eggs remaining gradually decreases
• the proportion of eggs with chromosomal abnormalities gradually increases
• the chance of pregnancy falls
• the risk of miscarriage rises.

Understanding these changes can help women make informed decisions about family planning, fertility treatment and egg freezing. 

As we age, not only does the number of eggs decrease steadily throughout life, the quality of those that remain also decreases. Older eggs are more likely to have chromosomal irregularities, such as fragmentation, which reduces the likelihood of embryos implanting and pregnancies progressing.

The result is that the chance of pregnancy falls as a woman gets older, and the risk of miscarriage and abnormalities increases, even for people with no fertility problems. If you have been trying to conceive for some time without success, the sooner you seek help, the better your chance of having a baby.

Women are born with ovaries containing over a million eggs. These eggs die over time through a natural process, leaving an average of 400,000 at puberty and fewer than 1,000 at menopause. Not all women lose eggs at the same rate. While many women remain fertile into their late 30s, some experience a more rapid decline and may lose fertility earlier than expected.

The term ovarian reserve refers to the number of eggs remaining in the ovaries.

The best blood test currently available to estimate ovarian reserve is the Anti-Müllerian Hormone (AMH) test.

AMH is produced by small growing follicles within the ovary. The level of AMH in the blood provides an indication of the number of eggs remaining relative to other women of the same age.

AMH can help us:

• estimate ovarian reserve
• predict likely response to IVF stimulation
• estimate how many eggs may be collected in an IVF cycle
• identify women who may be at risk of earlier-than-average menopause.

What AMH does NOT tell you

This is one of the most important messages for patients: AMH is not a fertility test

AMH does not tell us:

• whether you can become pregnant naturally
• how quickly you will become pregnant
• whether your eggs are genetically normal
• whether you will have a baby.

A low AMH result does not mean you are infertile.

Similarly, a high AMH result does not mean you are more fertile than other women your age.

AMH is primarily a measure of egg quantity, not egg quality. Age remains the most important predictor of the chance of having a baby.

How do I get an AMH test?

Your GP can request an AMH test:

• it is a single blood test that can be done at any time during the menstrual cycle
• it can help predict how many eggs you are likely to obtain in an IVF cycle
• it may also identify women who may undergo early menopause, and therefore who may lose their fertility earlier than average
• your doctor or nurse will give you a separate blood form for the test and tell you where you can have your test done. The result is usually available a week or so after the blood has been taken. Your doctor will tell you the result in person, by telephone or by sending you a letter
• the interpretation of the AMH result will depend on your medical history, your family’s fertility history, lifestyle and other investigations into your fertility.
• in some areas of New Zealand the AMH test is not publicly-funded. The cost is typically $90 to $115 depending on the lab.

Interpreting AMH

We recommend an appointment with a fertility specialist to analyse the results of an AMH test, and to explain what they mean for you.

Like most fertility tests, an AMH test does not give a 'black and white' answer. We plot the AMH result on a graph, (see below), that shows the 10th, 25th, 50th and 75th centiles for AMH for women attending a fertility clinic. This lets you compare your results with women of a similar age and helps predict how your AMH level may change over the years. We have shaded areas of the graph green, orange and red to represent the average impact of your AMH level.

While AMH tells us about the number of eggs remaining, it does not tell us about the health of those eggs.

Egg quality is influenced predominantly by age.

Each egg contains chromosomes that must divide accurately when fertilisation occurs. As women age, chromosome separation becomes less reliable, increasing the chance that an egg contains too many or too few chromosomes. This is called aneuploidy.

Many women are surprised to learn that egg quality can decline even when AMH remains normal. This explains why:

• a 32-year-old woman with a low AMH may still have a good chance of pregnancy.
• a 42-year-old woman with a normal AMH may still face significant fertility challenges related to egg quality.

Age affects both quantity and quality, but quality is often the more important factor when it comes to achieving a healthy pregnancy.

Aneuploidy, miscarriage and fertility

As egg quality declines, chromosome abnormalities become more common.

Embryos with chromosome abnormalities are less likely to:

• implant successfully
• continue to develop normally
• result in the birth of a healthy baby.

This is why increasing maternal age is associated with:

• lower natural fertility
• lower IVF success rates
• higher miscarriage rates
• increased risk of certain chromosomal conditions such as Downs syndrome.

The majority of first-trimester miscarriages are thought to result from chromosomal abnormalities in the embryo.

For women, fertility begins to decline at around the age of 30, with this becoming more marked after 35, with an even steeper decline after 40. Fertility in men does also decreases, but much more slowly and less noticeably. This is why the option of egg freezing is attractive for those who are keen to have a family, but are not yet ready.

As a rough guideline, you may want to seek advice if:

• you are under 35 and have been trying to conceive for 6 months or more without success
• you are 35 or older and have been trying for 12 months or more without success
• you are over 40.

For most women, age best predicts the chance of conception each month. However, despite having regular menstrual cycles and normal periods, about 10% of women lose their fertility sooner than expected. These women should think about having a family in their 20’s or very early 30’s.

For some women, the effect of age kicks in early.

• About 10% of women experience menopause 5 years earlier than average – around the age of 45 instead of 50. Their fertility will fall 5 years earlier than average.
• About 1% of women go through menopause 10 years earlier than average, around the age of 35. Their fertility will fall 10 years earlier than average.

If you are having concerns, we suggest a chat with one of our experienced fertility nurses, free of charge. You will be able to discuss your individual situation and they will guide you as to next steps.

Alternatively, make an appointment to see one of our fertility specialists who will be able to assess your fertility and prepare a plan for you.

While there’s no male equivalent to menopause, and the age of the mother is more important where fertility is concerned, the number of sperm made each day, and their quality, do fall with a man’s age.

Pregnancies from older men show higher incidences of some types of abnormalities among children – such as schizophrenia and autism. The total risk of a child having a serious birth defect, (from the biological father, the mother, or newly arising in the child), increases from an average of 20 per 1000 children for men aged 20; to 26 per 1000 children for men aged 50.

A man’s age does not seem to affect the chance of success in fertility treatments such as IVF – at least up to the age of 50.

Knowing when to seek help can be confusing

Should you keep trying for a bit longer, or do you need to book an appointment to talk it through?

You can try our Biological Clock which estimates the rate of natural conception per month of someone having no fertility issues.

Talk to one of our experienced fertility nurses in a free, no obligation 20 minute telephone chat. Book now.