Age and Female Fertility

Delaying starting a family has become more common throughout the developed world including in Australia. The reasons for this trend are obvious and include a desire to achieve career and financial stability before starting a family. Of the 295,738 babies born in Australia 2010, a greater number were born to mothers aged between the ages of 35 and 39 (55,937), than to mother aged between 20 and 24 (42,067). Since 1999, women aged 30 to 34 have recorded the highest birth rate of all age groups, and the average age of Australian mothers who registered a birth in 2010 increased to 30.6 years, compared to 29.7 years in 1999.

However, whilst the potential advantages of delaying starting a family are obvious, there are also risks associated with such a delay.

With advancing female age the age-related risk of fertility problems rises, being 5% at age 25 and 30% at age 35. There is a decrease in fertility with advancing age. The age related decline in fertility becomes more noticeable after the age of 30, accelerates between 35 and 40, and then declines rapidly after the age of 40 to the extent that fertility is almost zero by the age 45. Only two in five of those who wish to have a child at 40 years of age will be able to do so naturally. Although pregnancies in women approaching 50 and beyond have been reported, it should be noted that these are rare.
The risk of miscarriage also increases with age. Between 25 and 29 years the risk of miscarriage is 10% and by 40 to 44 it has risen to 34%.
Advancing maternal age is associated with an increasing risk of chromosomally abnormal offspring such as Down syndrome. For example, at the age of 20 year the risk is 1 in 500 but by the age of 45 it has risen to 1 in 20.
Older women are at increased risk of complications in pregnancy including gestational diabetes, high blood pressure, small-for-dates babies, and premature birth.

Why does Female Fertility decline with Age?

Ageing of the ovaries is the most prominent factor in declining fertility with age. Women are born with their lifetime supply of eggs, and this supply gradually decreases with advancing age. In other words, women do not produce new eggs and as they age their supply of eggs in their ovaries decreases. At puberty the average woman has around 300,000 eggs in her ovaries. For each egg that is released (ovulated), a number do not mature and are absorbed by the body. Unfortunately, some women lose their eggs at a much more rapid rate.

Broadly speaking, a woman's ovarian reserve is the amount of good quality eggs remaining in her ovaries. As the rate of loss of eggs varies between women, it can be difficult to predict the amount of eggs and level of fertility a woman has as she ages. Therefore, measuring your remaining egg supply (ovarian reserve) can be an important part of fertility evaluation. There is a blood test called Anti-Mullerian Hormone (AMH) that can be used in order to help estimate your ovarian reserve, and this will be described below.

As a woman ages, the remaining eggs in her ovaries also age, making them less likely to fertilize and the resulting embryos become less likely to implant. Gynecological problems such as endometriosis, fibroids, and problems with ovulation tend to occur more frequently with advancing age, and these conditions can also reduce fertility.

For those reasons infertility investigations and treatment should start earlier in older women.

Anti-Mullerian Hormone (AMH) Testing

Anti-Mullerian Hormone (AMH) is a hormone produced by cells in small developing egg sacs (follicles) that contain an egg in a woman's ovaries. Therefore, AMH gives an indication of the number of eggs being produced during a woman's monthly cycle. The level of AMH in a woman's blood is a good indicator of her ovarian reserve and is helpful in assessing her fertility status. A low level of AMH suggests that there is a significant reduction in the remaining supply of eggs.

The AMH test does not seem to change over the course of the menstrual cycle, and so AMH can be tested by obtaining a blood sample at any time of the month.

For women undergoing IVF treatment, AMH results can be used to help choose the best dose of fertility medicine(s) used to stimulate the ovaries. AMH levels may help to identify women who are more likely to over-respond or hyper-stimulate during IVF treatment, and the dose of fertility medicine can be adjusted to minimize that risk. AMH may help to identify woman who have polycystic ovarian syndrome (PCOS). AMH can also help to identify women who have a lower pregnancy rate from fertility treatment.

Success of Fertility Treatment with Advancing Age

As with natural fertility there is an age-related decline in the success rate of fertility therapy. This is most noticeable from the age of 40 onwards. For example North American statistics for live birth rates per cycle of in-vitro fertilization are 15% at 40, 11% at 41, 8% at 42, 5% at 43 and 2% at 44. At Bubtree and Monash IVF we do not offer IVF treatment after a woman's 45^th birthday because the success rate of treatment is so low.

Other Options for Treatment

For women who have previously undergone fertility treatments such as IVF and there are age-related reasons why treatment has not worked, then there may be other options that could be considered. These include egg donation using eggs donated by younger woman and embryo donation.

Screening for Down Syndrome and Other Chromosomal Abnormalities in Pregnancy

This is generally done with a blood test and nuchal translucency ultrasound between 11 and 14 weeks. The ultrasound has to be done in an accredited facility. Other tests available for screening include amniocentesis and chorionic villus sampling. The various pros and cons of screening for these conditions would be discussed with you by your Obstetrician at the first antenatal visit.