WHY AGE IS IMPORTANT
AGE AND FERTILITY
In today’s society, age-related infertility is becoming more common because, for a variety of reasons, many women are waiting until their 30s to begin their families. Even though women today are healthier and taking better care of themselves than ever before, improved health in later life does not offset the natural age-related decline in fertility. It is important to understand that fertility declines as a woman ages because of the gradual decrease in quantity and quality of the eggs in her ovaries. This decline may take place much sooner than most women expect.
A woman is born with all the egg-containing follicles in her ovaries that she will ever have (about one million). Only about 300 will be ovulated during the reproductive years. The majority of follicles are not used up by ovulation, but through an ongoing gradual process of loss called atresia. Atresia is a degenerative process that occurs regardless of whether you are pregnant, have normal menstrual cycles, use birth control, or are undergoing infertility treatment.
FERTILITY IN THE AGING WOMAN
A woman’s best reproductive years are in her 20s. Fertility gradually declines in the 30s, particularly after age 35. Each month that she tries, a healthy, fertile 30-year-old woman has a 20% chance of getting pregnant. By age 40, a woman’s chance is less than 5% per cycle. These percentages are true for natural conception as well as conception using fertility treatment, including in vitro fertilization (IVF). Women do not remain fertile until menopause. The average age for menopause is 51, but most women become unable to have a successful pregnancy sometime in their mid-40s. Smokers appear to experience menopause about 1 year earlier than non-smokers.
Women who have a medical disorder, such as high blood pressure or diabetes, should talk with their health care provider before attempting pregnancy. It is important that health problems are under control before attempting pregnancy. The health care provider may suggest a change in medication or general health care before pregnancy as there are increased risks for older women. Conditions such as high blood pressure or diabetes develop more commonly in women who conceive after age 35. Preconception counseling is often beneficial as well. Children born to women over age 35 have a higher risk of chromosomal problems.
Women are less likely to become pregnant and more likely to have miscarriages because egg quality declines as the number of remaining eggs dwindle in number. These changes are most noted as she reaches her mid-to-late 30s. Therefore, a woman’s age is the most accurate test of egg quality. An important change in egg quality is the frequency of genetic abnormalities called aneuploidy (too many or too few chromosomes in the egg). As a woman gets older, more and more of her eggs have either too few or too many chromosomes. That means that if fertilization occurs, the embryo also will have too many or too few chromosomes. Most people are familiar with Down syndrome, a condition that results when the embryo has an extra chromosome 21. Most embryos with too many or too few chromosomes do not result in pregnancy at all or result in miscarriage. This helps explain the lower chance of pregnancy and higher chance of miscarriage in older women.
FERTILITY IN THE AGING MAN
Unlike the early fertility decline seen in women, a man’s decrease in sperm characteristics occurs much later. Sperm quality deteriorates somewhat as men get older, but it generally does not become a problem before a man is in his 60s. Though not as abrupt or noticeable as the changes in women, changes in fertility and sexual functioning do occur in men as they grow older. Despite these changes, there is no maximum age at which a man cannot father a child, as evidenced by men in their 60s and 70s conceiving with younger partners. As men age, their testes tend to get smaller and softer, and sperm morphology (shape) and motility (movement) tend to decline. In addition, there is a slightly higher risk of gene defects in their sperm.