It is a fact that fertility declines with ageing – in both men and women. The primary reason for this is that men and women produce fewer high-quality gametes (sperm for men, eggs for women) as they age. Although the process and details are different between men and women, the end result is the same.
When we are born, our ovaries contain all the eggs a woman will have. By the start of puberty, their number has already dropped to 100 000. For most women, this means that there are enough eggs to last from the start of menstruation until menopause. In women with low ovarian reserve or premature ovarian failure, the number is limited and fertility falls much earlier. Although there is no standard age at which a woman’s fertility begins to decline, population studies show that women’s fertility as a whole begins to decline sharply around the age of 35. At age 40, a woman’s chance of becoming pregnant within a year is about half of what it was at age 20. Each year after the age of 40, the chances of conceiving naturally continue to fall sharply, and women over 44 have less than a 2% chance of conceiving using their own eggs. The graph below shows how age affects fertility.
Pregnancy is not the only difficulty that becomes more common with age. The rate of miscarriages rises sharply when women reach the age of 40, reaching 50%, compared with 10% in their 20s. Pregnancy complications can also increase, especially factors such as diabetes and heart disease. The risk of genetic problems increases with age. At 40, the risk of having a child with Down’s syndrome is around 1 in 100; by 45, it is already around 1 in 30.
Although complications increase with age, getting pregnant is not impossible, and many women over 40 have happy, healthy babies. It’s important to remember that each of us ages at a different rate – the best way to determine your reproductive age is through ovarian reserve testing. If your ovarian reserve is already reduced, there are many options to improve your chances of experiencing motherhood. These include IVF, egg donation, birth control, natural treatments such as acupuncture or supplements, and adoption. For younger women who, for one reason or another, put off starting a family, egg retrieval and storage can significantly increase the chances of getting pregnant later in life.
Age also affects male fertility. In addition to a decline in sexual activity, men’s germ cell production also declines with age. A 2006 study, Fertility and Sterility (Killick et al.), found that men over 45 took on average five times longer to conceive with a female partner than men under 25. Although men continue to produce sperm throughout their lives, their quality and quantity declines with age, partly due to age-related testosterone depletion. Between the ages of 30 and 50, important measures of sperm health, such as motility and morphology, can decline by up to 50%. These measures are important because they indicate the genetic health of sperm. Older men with less healthy sperm are not only less likely to help their partner get pregnant, but are also more likely to contribute to genetic abnormalities in the fetus.
Medical science is still exploring the role of men in passing on genetic information, but new research suggests that younger male partners also produce healthier offspring. Thus, while men may still be fertile beyond the age of 60, declining fertility rates and an increase in genetic abnormalities may have significant effects on fertility.