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Home > Learn > Fertility Treatments > >A Review of the Major Causes of Infertility

A Review of the Major Causes of Infertility

Dec 27, 19 9 min

A brief summary of major lifestyle and health factors that cause infertility so you feel better equipped to understand some of the barriers people may face while trying to conceive.

By Dr. Nazaneen Homaifar

If you’ve been trying to get pregnant for a year, and haven’t been able to conceive, it makes sense to see a doctor and to start understanding potential causes of infertility. (For women 35 and over, it’s recommended to see a doctor after six months of trying and being unable to conceive). 

First, we want to unpack the term “infertility.” It sounds so final, like once you have that diagnosis, there is no escaping it—but that’s not true. Infertility doesn’t mean an irreversible inability to get pregnant, but rather prolonged difficulty with getting pregnant. Many couples—with one of the diagnoses we’ll describe below—get pregnant, but sometimes it requires some medical assistance.

Infertility doesn’t mean an irreversible inability to get pregnant, but rather prolonged difficulty with getting pregnant. 

We don’t want to overwhelm you with all the possible things that could go wrong—the opposite, actually. We want to equip you with the terms and knowledge that you need to navigate the tricky landscape of trying to get pregnant.

To make that happen, here are a few key terms we want to unpack:

  • Fecundity/fecundability—this sounds Shakespearean, but you might actually read or hear it from your doctor. It refers to your likelihood of getting pregnant in the span of any given menstrual cycle, rather than in your general lifetime (we refer to this as fertility/infertility).
  • Female vs. male infertility—these terms refer to the fact that fertility issues within a heterosexual couple can stem from either partner. You might also see this written as “female-factor” or “male-factor” infertility.
  • Anatomy or process-specific “factors” (i.e. “tubal factor,” “ovulatory factor,” etc.)—conception is a complex process, and sometimes certain symptoms or physical findings allow your doctor to figure out which part of your body is contributing to infertility. These “factor” phrases are umbrella terms that allow clinicians to describe problems with that part or process. In women, doctors tend to divide the different factors into the following: ovulatory dysfunction, endometrial or uterine factor, tubal factor, and cervical factor. 

In rough terms, about one-third of infertility cases are attributed to male factors and one-third to female factors. For the remaining one-third of infertile couples, the cause is a combination of problems in both partners or, in about 20% of cases, it is unexplained. We’ll go over the most common causes for female and male infertility below. 

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Common causes of female infertility

1. Lifestyle factors

Healthy lifestyle habits are vitally important when you’re trying to get pregnant, and certain habits can harm your fertility.

  • Weight outside the healthy range for your height. Being either underweight or overweight can inhibit the body from conceiving because it can disrupt the body’s natural ovulation cycle. 
  • Untreated sexually transmitted infections (STIs). Some STIs, like gonorrhea and chlamydia, can cause scarring in the fallopian tubes, which prevents the egg from traveling down to be fertilized by sperm. 
  • Cigarette smoking. Smoking cigarettes makes conception less likely, as it can harm the eggs. One study found that it reduced the likelihood of getting pregnant by 50%. It also increases the risk of miscarriage significantly. Excessive alcohol and drug use can also cause problems for female fertility.
  • Environmental pollutants and toxins, such as flame retardants and dry cleaning solvents, heavy metals like mercury and arsenic, pesticides, and possibly bisphenol A (BPA) can have adverse effects on fertility and pregnancy. It can be challenging to assess the degree of exposure, the effect of exposure, and what to do to reduce exposure. Researchers are still studying effects on reproductive health outcomes for some of these toxins. If you would like to read more, check out the patient information guides at this UCSF website.

2. Age and pregnancy

Age also affects fertility, and those effects happen to women at a younger age on average than they do men. For a healthy woman in her 20s or early 30s, the chances of conceiving each month is 25%-30%. But by the time a woman is 40 years old, the chances are 10% or less each month. For women, this has to do with the quantity and quality of eggs and the decline that starts in the mid-30s. Women are born with a finite number of eggs, and menopause marks the permanent end of fertility because all of the eggs are depleted. As the quantity and quality of eggs decrease with age, the chance of gene defects increases. This also increases the chances of miscarriage. It’s certainly possible to get pregnant at a later age, but it can be more difficult. As noted, ACOG and ASRM recommend that women 35 and over start an infertility workup after six months of trying and not being able to get pregnant. 

3. Hormonal disorders

Ovulation is an essential part of the conception process, so it should make sense that any hormonal conditions that throw off ovulation can contribute to infertility. Hormonal disorders can occur as a result of conditions that affect the hypothalamus or pituitary of the brain (for example, small brain tumors called prolactinomas), thyroid (think of hypothyroidism), ovaries, or adrenal glands. Polycystic ovarian syndrome (PCOS) and primary ovarian insufficiency are two conditions that can disrupt ovulation and lead to difficulty conceiving. 

4. Structural problems

Structural causes of infertility can be thought of as physical barriers in the anatomy that can reduce the chances of pregnancy. They can include any of the following:

  • Blockage of the cervix
  • Fibroids in the lining of the uterus 
  • Scarring of the fallopian tubes (from unchecked STIs)
  • Abnormally formed organs
  • Scar tissue from endometriosis or previous surgeries in the uterus

In order to check for scarring or blockage in the fallopian tubes, your doctor will likely order you for a hysterosalpingogram, which is a real-time x-ray study using fluoroscopy to look at the uterus and tubes. Dye is injected into the uterus through the cervix and images are taken to see if the dye passes through the fallopian tubes. A pelvic ultrasound is used to assess the anatomy of the uterus to check for fibroids. 

Common causes of male infertility

Male factor is a contributing cause of a couple’s infertility in about 30-40% of couples. 

1. Male reproductive system

There are fewer factors involved in male fertility related to the sperm:

  • Semen volume: the amount of fluid expelled in the ejaculate. Sperm makes up about 5% of the volume in ejaculatory fluid (most of it is fluids from the prostate and seminal vesicles). Azoospermia is the medical term for when there is no sperm present in semen.
  • Sperm concentration: the number of individual sperm per milliliter of semen. Oligospermia is the medical term for low sperm count
  • Sperm motility: your swimmers’ ability to move efficiently through the female reproductive tract. A semen analysis will look at the percentage of motile sperm, which should be 40% or higher. Progressive motility, the rate of forward movement, is also measured. Asthenospermia is what we call low sperm motility or “slow swimmers.”
  • Sperm morphology: the shape and size of the sperm. A normally shaped sperm is a mere three micrometer-wide oval with a distinctive tail. Misshapen sperm, also called teratozoospermia, can also cause infertility. 

To evaluate sperm, a doctor will recommend a semen analysis, which looks at the measures above as well as a host of other factors including: pH (which should be between 7.2 and 8.0), sperm agglutination (the amount of sperm that stick to one another from a sample), total sperm count, viscosity (the rate at which semen liquefies), and more. These can all factor into your ability to conceive successfully. You might also consider using a fertility-friendly lubricant during sex when trying to conceive, to ensure that the lube you’re using isn’t getting in the way of your goal. Another option is taking a sperm test at home to determine the health and quality of your sperm prior to going to the doctor.

2. Lifestyle factors

Like female fertility, male fertility is also strongly affected by lifestyle factors. 

  • Just as with women, untreated STIs in men can lead to fertility issues. It is important to get tested, especially if you haven’t been in a while.
  • Cigarette smoking and excessive drug and alcohol use are associated with lower sperm counts.
  • Exposure to harmful chemicals, toxins, and radiation can harm sperm quality and DNA. These include steroids, chemotherapy and radiation, some pesticides, and heavy metals.
  • Exposure to heat can also be harmful for sperm and has been shown to be a weakly associated risk factor for infertility. That being said, it’s prudent to try and limit exposure to excessive heat sources like saunas, hot tubs, and your laptop. (Another reason to get a standing desk!)

3. Age

Age can affect both female and male fertility, although not to the same extent or timeframe. With age, the testes tend to get smaller and softer, and the sperm shape and movement tend to decline. Unlike women, men remain fertile from puberty onward—there’s no male menopause—although men over the age of 50 may be less fertile because of the physiological changes we mentioned. Studies have shown that increasing paternal age is related to changes in sperm DNA and can result in gene defects, but the degree of risk is not nearly as high as what we see with increasing maternal age. Despite these changes, there is no maximum age at which a man can father a child.  

4. Conditions leading to infertility

There are a number of congenital, acquired, and systemic conditions that can contribute to male infertility. Cystic fibrosis, an autosomal recessive disease, causes defects in sperm transport and causes infertility in 95% of men born with it. Klinefelter syndrome, caused by an extra chromosome, results in low testosterone and sperm production. Poorly-controlled diabetes causing chronic kidney failure has a known effect on male fertility. Other conditions, like malnutrition and sickle cell anemia, or infections, like mumps, can also affect sperm quality. 


Going through the list of factors that can affect fertility always reminds me of what a mind-bogglingly precise science must exist for conception to happen! As you can see, there are many aspects that can factor into your ability to conceive. We hope you’ll leave with a higher level of understanding of barriers and feel better equipped to discuss potential concerns. Please talk to your doctor about any concerns; ultimately, they will help decide on what evaluations or tests may be necessary based on your history.

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