How aging affects fertility and pregnancy

Age is the main factor that affects fertility in both males and females. This decline may take place much sooner than most people expect.

Men experience changes in sperm characteristics and sexual functioning, while women see a decrease in the quality and quantity of eggs. 

Fertility in the aging female
Research shows that women tend to be most fertile in their 20s. Your fertility starts declining around age 32 and declines more rapidly starting around age 35. By age 40, a woman’s chance is less than 5% per cycle, so fewer than 5 out of every 100 women are expected to be successful each month.

As a woman ages, the risk of miscarriage, preterm birth, or chromosomal abnormalities in the baby increases. Also, the risk of complications during pregnancy. 

Women do not remain fertile up until menopause. The average age for menopause is 51, but most women become unable to have a successful pregnancy sometime in their mid-40s. These percentages are true for natural conception as well as conception using fertility treatment, including in vitro fertilization (IVF). A woman’s age affects the success rates of infertility treatments. The age-related loss of female fertility happens because both the quality and the quantity of eggs gradually decline.

Egg quantity
The number of eggs naturally decreases with age. Women begin life with a fixed number of eggs in their ovaries. These have been produced since they were a fetus in their mother’s womb, numbering around 6 to 7 million. 

Follicles, a sac-like filled with eggs, are gradually recruited to grow through a woman’s reproductive age. Once a follicle is triggered to re-initiate development, it enters into multiple growing follicles. Most mature ones will continue their way for fertilization and others will disintegrate along the way. The number of oocytes decreases to approximately 1–2 million oocytes at birth. By puberty, only 300,000 of the egg cells are available for ovulation. 

Shorter cycles
As ovarian reserve declines, the follicles become less and less sensitive to FSH stimulation, so they require more stimulation for an egg to mature and ovulate. At first, periods may come closer together resulting in short cycles, 21 to 25 days apart. Eventually, the follicles become unable to respond well enough to consistently ovulate, resulting in long, irregular cycles. Diminished ovarian reserve is usually age-related and occurs due to the natural loss of eggs and a decrease in the average quality of the eggs that remain.

Some younger women have a condition known as reduced ovarian reserve, which has similar outcomes to aging. This is caused by several different genes, the best known of which is the Fragile X gene, which causes learning difficulties in affected males. Women carrying this gene have low ovarian reserves and higher risks of having babies with chromosome abnormalities, as well as sons with fragile X.

Ways to measure egg count
There are two good ways to measure egg count: an antral follicle count and an AMH (anti-Müllerian hormone) test. 

For an antral follicle count, a doctor uses ultrasound to count the visible follicles. AMH, on the other hand, is a protein hormone produced by special cells inside the follicles. This helps estimate the total number of follicles inside the ovaries. But no single test nor any combination of tests is 100% accurate. And none have been proven to reliably predict the possibility of becoming pregnant. However, age remains the best predictor of pregnancy.

Egg quality
women in their 20s will have mostly normal eggs, though they already have some abnormal ones. And women in their 40s will have mostly abnormal eggs—no matter how healthy a lifestyle they maintain.

The remaining eggs in older women are more likely to have abnormal chromosome division. During division progression, older eggs tend to accumulate errors in their DNA, leading to genetically abnormal eggs called Aneuploidy (too many or too few chromosomes in the egg). Nevertheless, the overall risk of having a baby with a chromosomal abnormality is small. 

There’s no test for egg quality. The only way to know if an egg is chromosomally normal is to attempt to fertilize it, and, if fertilization is successful, to perform a genetic test on the embryo. However, because DNA damage in older eggs is inevitable, a woman’s age can give doctors a fairly accurate estimate of the percentage of her eggs that are likely to be genetically normal.

Fertility in the aging male
Many people tend to think of fertility as something that pertains primarily to women, but in actuality, at least 30% of infertility cases can be attributed to male-factor infertility. 

Male fertility does decline throughout adulthood, but it doesn’t have a significant effect on fertility until a man is in his 40s, as there’s only about a 1–2% decrease in sperm quality per year. Sperm is renewed daily, but still, a healthy man experiences male fertility decline. 

Sperm health depends on various factors, including movement, structure, and quantity. The change in sperm character may increase the time to pregnancy, decrease pregnancy rates and increase the risk of miscarriage. 

Men do experience a decline in fertility, but they don’t necessarily become infertile as a result of age. The testis can still produce the male hormone testosterone and sperm cells. Therefore, it is possible for men of any age to father a biological child.

Sperm quantity
A normal sperm count ranges from 15 million sperm to more than 200 million sperm per milliliter (mL) of semen. Anything less than 15 million sperm per milliliter, or 39 million sperm per ejaculate, is considered low. Too little sperm in an ejaculation might make it more difficult to get pregnant because there are fewer candidates available to fertilize the egg.

There may be a very little decrease in seminal volume with age. The most pronounced changes occur in men over age 45. Some studies, on the other hand, show no difference in volume with age, so the impact this has on male fertility decline is not clear.

To measure the sperm quality and quantity. The method can be done by semen analysis under a high-power microscope. This may help to find the cause of infertility. 

Sperm quality
The quality of sperm deteriorates as men get older, but it generally does not become a significant problem until age 45s. 

Normal sperm have oval heads and long tails, which work together to propel them. While not as important a factor as sperm quantity or movement, the more sperm you have with a normal shape and structure, the more likely you are to be fertile. A lower number of normally shaped sperm results in male fertility decline. Studies indicate that normal sperm structure declines .2–.9% per year, resulting in a 4–18% decrease in normal morphology over a 20-year period.

To reach and fertilize an egg, sperm must move — wriggling and swimming through a woman’s cervix, uterus, and fallopian tubes. This is known as motility. Motility is developed as the sperm travel through the prostate and the epididymis, so motility decrease is thought to be due to age-related decline in the function of these glands.

There’s evidence that the chance of miscarriage increases with paternal age, potentially due to genetic abnormalities in the sperm. Children of older fathers also have an increased risk of mental health problems (although this is still rare). Children of fathers aged 40 or over are 5 times more likely to develop an autism spectrum disorder. They also have a slightly increased risk of developing schizophrenia and other mental health disorders later in life.

To help improve sperm quality, you may try exercise, stop stressing, quit smoking, stop using drugs, and eat healthy food.