Fertility changes with age. Both males and females become fertile in their teens following puberty. For girls, the beginning of their reproductive years is marked by the onset of ovulation and menstruation. It is commonly understood that after menopause women are no longer able to become pregnant. Generally, reproductive potential decreases as women get older, and fertility can be expected to end 5 to 10 years before menopause.
During their reproductive years, women have regular monthly menstrual periods because they ovulate regularly each month. Eggs mature inside of fluid-filled spheres called “follicles.” At the beginning of each menstrual cycle when a woman is having her period, FSH produced in the pituitary gland, stimulates a group of follicles to grow more rapidly on both ovaries. Normally, only one of those follicles will reach maturity and release an egg (ovulate); the remainder gradually will stop growing and degenerate. Ovulation is the release of an egg from a woman’s ovaries and is essential for getting pregnant. Ovulation is spontaneously triggered about 36-40 hours after blood levels of a luteinizing hormone (LH) rise. Once released from the ovary, the egg is picked up by and travels down the fallopian tube where it can meet sperm. Pregnancy results if the egg becomes fertilized by sperm and implants in the lining of the uterus (endometrium). If pregnancy does not occur, the endometrium is shed as the menstrual flow and the cycle begins again.
Infertility is “the inability to conceive after 12 months of unprotected intercourse.” This means that a couple is not able to become pregnant after a year of trying. However, for women aged 35 and older, inability to conceive after 6 months is generally considered infertility. Infertility affects 10%-15% of couples. This makes it one of the most common diseases for people between the ages of 20 and 45
As women age, fertility declines due to normal, age-related changes that occur in the ovaries. Unlike men, who continue to produce sperm throughout their lives, a woman is born with all the egg-containing follicles in her ovaries that she will ever have. At birth there are about one million follicles. By puberty that number will have dropped to about 300,000. Of the follicles remaining at puberty, only about 300 will be ovulated during the reproductive years. The majority of follicles undergo atresia which occurs regardless of whether the woman is pregnant, have normal menstrual cycles, use birth control, or are undergoing infertility treatment
The decreasing quantity of egg-containing follicles in the ovaries is called “loss of ovarian reserve.” As ovarian reserve declines, the follicles become less and less sensitive to FSH stimulation, so that they require more stimulation for an egg to mature and ovulate Diminished ovarian reserve is usually age-related and occurs due to the natural loss of eggs and decrease in the average quality of the eggs that remain. However, young women may have reduced ovarian reserve due to smoking, family history of premature menopause, and prior ovarian surgery.
Women become less likely to become pregnant and more likely to have miscarriages because egg quality decreases as the number of remaining eggs dwindle in number. 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). At fertilization, a normal egg should have 23 chromosomes, so that when it is fertilized by a sperm also having 23 chromosomes, the resulting embryo will have the normal total of 46 chromosomes. 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 embryos with too many or too few chromosomes do not result in pregnancy at all or result in miscarriage
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. 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. Not all men experience significant changes in reproductive or sexual functioning as they age, especially men who maintain good health over the years.