Common Causes of Infertility in Women and Men

One in every eight couples suffers from infertility, which is a medical condition characterized by an inability to conceive a baby. According to experts, couples are considered infertile if they've been actively trying to get pregnant for at least one year without success—or 6 months if the woman is older than 35. Those who experience recurrent miscarriages might also be diagnosed with infertility.

Despite common misconception, infertility isn't solely a female problem. About 40 percent of cases stem from the woman, while 40 percent are related to the male, explains Timothy Hickman, M.D., the medical director of CCRM Houston and director of the Division of Reproductive Endocrinology and Infertility at Houston Methodist Hospital. The rest of the time, it's either a mix of both partners' conditions or unknown causes.

It helps to understand that baby-making is a complex process that's contingent upon four crucial steps:

1. A woman and man each producing eggs and sperm
2. Healthy fallopian tubes that allow the sperm to easily get to the egg
3. The sperm's ability to fertilize the egg upon reaching it
4. A fertilized egg's ability to attach to the uterus and continue developing normally

Infertility may result when there's a hiccup in one or more of these steps. Keep reading for more about male and female infertility causes, and learn about factors that can influence your baby-making success.

What Causes Infertility in Women?

Because conception is so complicated, there are a number of factors that can lead to infertility in women. Here are some of the most common ones.

Maternal Age

More than anything else, maternal age has the biggest impact on your ability to conceive, says Nicole Noyes, M.D., a reproductive endocrinology and infertility specialist at the NYU Langone Fertility Center. That's because women are born with all of their eggs, and the number of eggs (as well as their quality) decreases over time. Indeed, two-thirds of fertility potential is lost between 35 to 40 years old.

Fallopian Tube Damage

Fallopian tube disease accounts for about 20 percent of infertility cases treated, according to RESOLVE: The National Infertility Association.That's because if the fallopian tubes are scarred or blocked, sperm may struggle to reach the egg. A fertilized egg may also have difficulties traveling to your uterus to develop into a baby.

Fallopian tube damage can have many causes, including pelvic inflammatory disease (an infection that usually results from untreated sexually transmitted diseases like chlamydia and gonorrhea), endometriosis, or a prior ectopic pregnancy (where the fertilized egg implants outside of the uterus). Having very painful periods or a history of pelvic pain are common signs of fallopian tube damage.

Endometriosis

Endometriosis is a condition in which tissue from the uterine lining grows outside the uterus—often on the ovaries, fallopian tubes, bladder, and/or bowel. In some cases, women with endometriosis have no painful symptoms, and the condition can only be confirmed with an outpatient surgical procedure called a laparoscopy.

Endometriosis may lead to a build-up of scar tissue between the uterus, ovaries, and fallopian tubes—and this can hinder the transfer of the egg to the fallopian tubes. It can also cause endometrial cysts that grow inside the ovaries and prevent the release of the egg or its collection by the fallopian tube. What's more, endometriosis can make it difficult for the fertilized egg to adhere to the uterine wall.

Ovulation Problems

If you don't ovulate normally, then you're not releasing healthy eggs for sperm to fertilize. Ovulation problems often result from hormonal imbalances. The female sex hormones LH, FSH, and estrogen are needed to launch an egg each menstrual cycle—and if they're released at the wrong time or in the wrong amounts, it can throw off ovulation. The main symptoms of ovulation roadblocks are irregular or missing periods.

Polycystic Ovarian Syndrome (PCOS)

Up to 10 percent of all women experience polycystic ovarian syndrome (PCOS). The condition causes a hormonal imbalance that triggers the body to produce excess testosterone, and it can also hinder ovulation. Women with PCOS may be overweight and have excess body or facial hair and acne, in addition to irregular or missing periods.

Uterus Problems

If an egg can't attach normally to the uterine wall, it can't continue developing into a healthy fetus. Uterus problems may be due to fibroids or polyps, which are benign tissue growths from the wall of the uterus; they may sometimes affect fertility depending on their size and location. Scar tissue in the uterus from infection, miscarriage, or abortion may also play a role. Unexplained lower abdominal pain or bloating may be a sign of uterine problems that can affect fertility.

Being Overweight or Underweight

Women with a body mass index (BMI) below 20 or above 27 are less likely to conceive than women with BMIs that fall within that range. The main reason: Weighing too little (from excessive exercise or not eating enough) or too much may throw your hormones off-balance and interfere with ovulation.

Sexually Transmitted Diseases

STDs like chlamydia and gonorrhea (both easily treatable with antibiotics) may lead to pelvic infections that interfere with conception.

Autoimmune Disorders

Diseases such as lupus, diabetes, thyroid disease, and rheumatoid arthritis can interfere with fertility.

Certain Medications

Antidepressants, antibiotics, painkillers, and other drugs used to treat chronic disorders may cause temporary infertility.

Tobacco or Alcohol Consumption

Research has shown that smoking cigarettes may interfere with ovulation and damage eggs, making them more prone to genetic defects that can lead to miscarriage. Plus, while an occasional cocktail hasn't been shown to do much harm, heavy drinking has been linked to infertility in women.

Environmental Hazards

Prolonged exposure to high mental stress, high temperatures, chemicals, radiation, or heavy electromagnetic or microwave emissions may reduce a woman's fertility.

Other Female Infertility Causes

The remaining causes of infertility in women may include uterine fibroids, immune system diseases, kidney disease and diabetes, premature menopause, and cancer and treatment for it (like chemotherapy and radiation).

What Causes Infertility in Men?

Most of the time, male infertility results from difficulty producing healthy sperm or a glitch in the sperm's ability to reach and fertilize an egg. Keep reading to learn about these problems, as well as other causes of infertility in men.

Sperm Motility Problems

To make a baby, it takes just one sperm to fertilize one egg—but the chances of any given sperm cell reaching and penetrating an egg are very slim. The more sperm released after ejaculation (a measure known as sperm count), the better your odds for conceiving. Men with 10 million or less sperm per milliliter of semen may have more fertility problems than those with normal sperm counts (20 million or more sperm per milliliter of semen). Note that low sperm count is known as oligospermia, while lack of sperm production is calledazoospermia.

Problems with sperm count may also result from varicocele—a varicose vein in the testicle that may keep the temperature too warm to produce sperm normally. Sperm that are abnormally structured might also struggle to make the long trek from the vagina to the fallopian tube, and they could have a hard time penetrating the egg once they do arrive.

Sperm motility problems could be caused by imbalances with testosterone or other hormones, abnormalities with the testicles, exposure to certain environmental toxins or chemicals, certain medications (like steroids), genetic conditions, infections like chlamydia and gonorrhea, or cancer.

Sperm Production Problems

It sounds obvious, but sperm needs to leave the penis in order to reach the egg—and male infertility sometimes results from issues or blockages that prevent this from happening. Causes include sexual problems (like premature ejaculation or trouble maintaining an erection), retrograde ejaculation (when semen flows into the bladder instead of out through the penis), and blockages in the testicles or tubes that carry sperm.

Certain conditions make some sperm production problems more likely. For example, diabetes, bladder issues, and prostate issues may affect retrograde ejaculation. Men with cystic fibrosis often have problems with the vas deferens, the tube that transports sperm from the testicles to the penis.

Smoking and Alcohol Use

Research shows that cigarettes and tobacco negatively influence male fertility, likely by reducing semen quality. Moderate drinking is unlikely to impact fertility, but consuming enough alcohol to harm the liver or other organs can make men less fertile by lowering testosterone, shrinking the testicles, causing difficulty getting an erection, and slowing sperm mobility.

Certain Drugs and Medicines

Using marijuana or cocaine has been shown to decrease sperm quality and quantity. Along those lines, certain drugs (such as steroids) may also affect sperm quality.

Toxic Substances

Chronic exposure to elements such as lead, cadmium, mercury, hydrocarbons, pesticides, radioactivity, and X-rays may have an impact on sperm count and quality.

Obesity

Being significantly overweight can throw off hormones that affect male fertility. One study found that a 20-pound weight gain can increase infertility in men by 10 percent.

Heat Exposure

The frequent use of saunas, steam rooms, hot tubs, whirlpools, and hot baths might temporarily impair sperm production and reduce sperm count.

Some Medical Conditions

Men with a history of prostatitis or genital infection, mumps after puberty, surgery on their hernia, undescended testicles, or scrotal varicose veins (varicocele) may also experience a decrease in fertility.

Sexually Transmitted Diseases

STDs like chlamydia and gonorrhea may lead to damage in the testicles that cause scarring, blocking sperm.

When to Visit a Doctor for Infertility

Are you wondering if you should visit a fertility specialist? It really depends on your age and certain known health conditions. In general, visit a doctor if the woman is under 35, and you've been unsuccessfully trying to get pregnant for more than one year. Also make an appointment if the woman is 35 or older, and you've been trying to conceive for more than 6 months.

Women of any age with the following symptoms should also visit the doctor:

• Irregular periods (a sign you may not be ovulating normally)
• Very painful periods (which signals you may have pelvic inflammatory disease or endometriosis)
• A history of polycystic ovarian syndrome
• A history of miscarriage

Men and women are often evaluated for fertility problems at the same time. That said, men with sexual problems, health conditions, and risk factors known to impact fertility may want to get checked out sooner.

• RELATED: A Guide to Infertility Treatment Options

Remember, if you're still seeing the negative sign on the pregnancy test after a few months of trying, you may simply need more time. In any given month, your baby-making odds are slim—only about 20 percent during your 20s and 30s. It sometimes takes completely fertile couples many months to conceive naturally.