Factors Affecting Fertility

Last updated: Wed, 04/26/2017 - 11:00

1.  AGE

What age-related factors may be involved with infertility in females and males?

Fertility naturally declines as females and males get older.

For instance, a female is born with all the eggs she will ever have naturally. Researchers currently believe that women are born with 1 million to 2 million eggs and that this number decreases throughout the lifespan. The decrease in fertility accelerates over time because of the reduction in the number and quality of eggs in the ovaries.  The lower number of eggs leads to changes in hormone levels, which further reduces a woman's fertility. After a woman goes through menopause, there is no way for her to get pregnant naturally.

New research suggests that researchers may be able to create eggs from stem cells in the ovaries.  The discovery of how to make eggs from stem cells could help women preserve their fertility or could remove age as a factor in infertility.

Increasing age also increases the risk for certain problems that can contribute to a loss of fertility.  These include:

  • Uterine fibroids
  • Tubal disease, a general term that describes any number of infections that affect the fallopian tubes
  • Endometriosis
  • Genetic abnormalities of the remaining eggs, which can make them less viable or increase the likelihood that an infant will have conditions such as Down syndrome

In addition, lifestyle and environmental factors can combine with age-related factors to significantly decrease fertility.

As a woman ages, the risk increases for miscarriage and for having an embryo with abnormal chromosomes, which can lead to problems with development and loss of the pregnancy.

In males, age is known to reduce the quality of sperm, which affects the sperm's ability to reach or fertilize an egg. Men also produce fewer sperm as they age.

Other age-related causes of reduced fertility in males include:

  • Genetic abnormalities of the sperm, which can reduce the chances of their partner becoming pregnant or increase the likelihood of miscarriage or of an infant having a condition such as Down syndrome
  • Erectile dysfunction, which can be affected by decreasing testosterone levels as a man ages or by medications for age-related conditions such as hypertension
  • Changes to the reproductive tissues or organs. For example, testicle volume decreases with age. Also, men may have an enlarged prostate, which can cause problems with ejaculations.


What lifestyle and environmental factors may be involved with infertility in females and males?

Research consistently shows that lifestyle factors—what you eat, how well you sleep, where you live, and other behaviors—have profound effects on health and disease. Fertility is no exception.

A number of lifestyle factors affect fertility in women, in men, or in both. These include but are not limited to nutrition, weight, and exercise; physical and psychological stress; environmental and occupational exposures; substance and drug use and abuse; and medications.

For example, research shows that:

  • Obesity is linked to lower sperm count and quality in men.
  • Among obese women who have polycystic ovary syndrome (PCOS), losing 5% of body weight greatly improves the likelihood of ovulation and pregnancy.
  • Being underweight is linked to ovarian dysfunction and infertility in women.
  • Strenuous physical labor and taking multiple medications are known to reduce sperm count in males.
  • Excessive exercise is known to affect ovulation and fertility in women.
  • Research shows that using body-building medications or androgens can affect sperm formation.
  • Substance use, including smoking tobacco, using other tobacco products, marijuana use, heavy drinking, and using illegal drugs such as heroin and cocaine reduce fertility in both men and women.
  • Having high blood pressure changes the shape of sperm, thereby reducing fertility.
  • The type of underwear a man chooses is not related to his infertility.
  • Radiation therapy and chemotherapy can cause infertility in females and males. Those who have to undergo these types of treatments may want to consider fertility preservation.

NICHD research also shows that exposure to persistent organic pollutants and endocrine-disrupting chemicals (EDCs) in the environment can also affect male and female fertility.

Persistent organic are currently used or were formerly used in industrial processes and remain in the environment much longer than other chemicals. Animal studies suggest that exposure to certain persistent organic pollutants affects fertility. NICHD’s Longitudinal Investigation of Fertility and the Environment (LIFE) Study is examining whether exposure to persistent organic pollutants affects the length of time it takes for couples to become pregnant, a measure of fecundity. It is the only study to measure chemicals in both partners and to follow couples trying to become pregnant for 1 year.

So far, the study has found that certain kinds of organochlorine pesticides and many polychlorinated biphenyls (PCBs) were linked to increased time-to-pregnancy or decreased couple fecundity.  The study found that many chemicals only affected time-to-pregnancy when found in high levels in the male partner, whereas other chemicals only affected fecundity when detected in the female partner. Other studies have linked exposure to TCCD dioxin and select polybrominated diethers and perfluorochemicals to reduced fecundity.

EDCs alter the function of the hormonal system, a key component in fertility. The LIFE study found that the EDC methyl paraben affects fertility in women, while phthalates and the UV filter benzophenone-2 affect fertility in men.



What do we know about idiopathic or unexplained infertility in females and males?

When health care providers cannot find a specific or even likely cause for infertility in females or males, they will diagnose the infertility as “idiopathic” or unexplained.

This diagnosis applies to about 30% of female infertility cases and about 50% of male infertility cases.

In some cases, however, knowing the exact cause may not be necessary. The health care provider may begin treatment to improve the chances of conception, including fertility treatments, even if no cause can be identified.


If you have specific questions about your own fertility or infertility, you should talk with your health care provider.


Courtesy: Eunice Kennedy Shriver National Institute of Child Health and Human Development.