Fertility is defined as the capacity to produce a child. It is generally observed that 80% of couple will conceive in the first six months of attempting pregnancy (Gnoth 2003). The monthly fecundity (the probability of pregnancy per month) is greatest in the first 3 months. The fertility rate is reduced by half among women in their late 30s compared to women in their early 20s (Dunson DB 2004). This proved that age alone is the most important predictor of fertility.
Studies has shown that the pregnancy rate was 74% in women younger than 31 years compared to 62% for women ages 31-35 years and 54% for women older than 34 years of age. Even with state of art IVF technology, the livebirth rate for younger than 35years was 41.5%, compared to at 12.1% at 40-44 years old. The fertility rate decreases with increasing maternal age.
Reasons for a reduced fertility rate
The numbers of eggs in the woman’s ovaries are finite. It decreases naturally and progressively with age. The total number of eggs is approximately 1 million at birth, 500,000 at puberty and is reduced to 1000 at menopause. The availability of eggs is one of the essential process of conception. Fecundity defined as ability to conceive, decrease gradually but significantly at age of 32, then rapidlyly after age of 37.
Besides this natural loss, there is also a deterioration of egg quality as demonstrated by increasing FSH and decreasing AMH. The risks of other disorders associated with ageing such as fibroid, tubal disease and endocrine condition may adversely affect the woman’s fertility.
Increase miscarriage rate in elderly mother
Early pregnancy loss has also showed an increasing trend with advance maternal age. This is partly due to increase in abnormal chromosome (aneuploidy), especially autosome trisomies. The incidence of spontaneous miscarriage is 10% in women younger than 30 years; 20% in 41-42 years and 36.6% in older than 42 years
Women should be aware of the effect of age on fertility, should they choose to delay starting a family. Given the decline in fertility, increase in pregnancy loss and pregnancy risk with aging, women older than 35 years should seek early medical attention if they fail to conceive after 6 months of attempting pregnancy. For women who are older than 40 years, immediate evaluation and treatment are warranted.
Dunson DB et al., Am J Obstet Gynecol 2004
Gnoth C et al., Human Reproduction 2003