Most experts define infertility as not being able to get pregnant after at least one year of trying. Women who are able to get pregnant but then have repeat miscarriages are also said to be infertile.

Pregnancy is the result of a complex chain of events. In order to get pregnant:

A woman must release an egg from one of her ovaries.
The egg must go through a fallopian tube toward the uterus
A man’s sperm must join with the egg along the way
The fertilized egg must attach to the inside of the uterus.
Infertility can result from problems that interfere with any of these steps.

Yes. About 6% of married women 15–44 years of age in the United States are unable to get pregnant after one year of unprotected sex (infertility).

Also, about 12% of women 15–44 years of age in the United States have difficulty getting pregnant or carrying a pregnancy to term, regardless of marital status (impaired fecundity).

Source: CDC

No, infertility is not always a woman’s problem. Both men and women contribute to infertility.

Many couples struggle with infertility and seek help to become pregnant; however, it is often thought of as only a women’s condition. A CDC study analyzed data from the 2002 National Survey of Family Growth and found that 7.5% of all sexually experienced men younger than age 45 reported seeing a fertility doctor during their lifetime—this equals 3.3–4.7 million men. Of men who sought help, 18% were diagnosed with a male-related infertility problem, including sperm or semen problems (14%) and varicocele (6%).

Source: CDC

Infertility in men can be caused by different factors and is typically evaluated by a semen analysis. A specialist will evaluate the number of sperm (concentration), motility (movement), and morphology (shape). A slightly abnormal semen analysis does not mean that a man is necessarily infertile. Instead, a semen analysis helps determine if and how male factors are contributing to infertility.

Conditions that can contribute to abnormal semen analyses include—

Varicoceles, a condition in which the veins on a man’s testicles are large and cause them to overheat. The heat may affect the number or shape of the sperm.
Medical conditions or exposures such as diabetes, cystic fibrosis, trauma, infection, testicular failure, or treatment with chemotherapy or radiation.
Unhealthy habits such as heavy alcohol use, testosterone supplementation, smoking, anabolic steroid use, and illicit drug use.
Environmental toxins including exposure to pesticides and lead.
Source: CDC

Women need functioning ovaries, fallopian tubes, and a uterus to get pregnant. Conditions affecting any one of these organs can contribute to female infertility. Some of these conditions are listed below and can be evaluated using a number of different tests.

Ovarian Function (presence or absence of ovulation and effects of ovarian “age”):

Ovulation. Regular predictable periods that occur every 24–32 days likely reflect ovulation. Ovulation can be predicted by using an ovulation predictor kit and can be confirmed by a blood test to see the woman’s progesterone level. A woman’s menstrual cycle is, on average, 28 days long. Day 1 is defined as the first day of “full flow.”
A woman with irregular periods is likely not ovulating. This may be because of several conditions and warrants an evaluation by a doctor. Potential causes of anovulation include the following:
Polycystic ovary syndrome (PCOS). PCOS is a hormone imbalance problem that can interfere with normal ovulation. PCOS is the most common cause of female infertility.
Functional hypothalamic amenorrhea (FHA). FHA relates to excessive physical or emotional stress that results in amenorrhea (absent periods).
Diminished ovarian reserve (DOR). This occurs when the ability of the ovary to produce eggs is reduced because of congenital, medical, surgical, or unexplained causes. Ovarian reserves naturally decline with age.
Premature ovarian insufficiency (POI). POI occurs when a woman’s ovaries fail before she is 40 years of age. It is similar to premature (early) menopause.
Menopause. Menopause is an age-appropriate decline in ovarian function that usually occurs around age 50. It is often associated with hot-flashes and irregular periods.
Ovarian function. Several tests exist to evaluate a woman’s ovarian function.
No single test is a perfect predictor of fertility.
The most commonly used markers of ovarian function include follicle stimulating hormone (FSH) value on day 3–5 of the menstrual cycle, anti-mullerian hormone value (AMH), and antral follicle count (AFC) using a transvaginal ultrasound.
Tubal Patency (whether fallopian tubes are open, blocked, or swollen):

Risk factors for blocked fallopian tubes (tubal occlusion) can include a history of pelvic infection, history of ruptured appendicitis, history of gonorrhea or chlamydia, known endometriosis , or a history of abdominal surgery.
Tubal evaluation may be performed using an X-ray which is called a hysterosalpingogram (HSG), or by chromopertubation (CP) in the operating room at time of laparoscopy, a surgical procedure in which a small incision is made and a viewing tube called a laparoscope is inserted.
Hysterosalpingogram (HSG) is an X-ray of the uterus and fallopian tubes. A radiologist injects dye into the uterus through the cervix and simultaneously takes X-ray pictures to see if the dye moves freely through fallopian tubes. This helps evaluate tubal caliber (diameter) and patency.
Chromopertubation is similar to an HSG but is done in the operating room at the time of a laparoscopy. Blue-colored dye is passed through the cervix into the uterus and spillage and tubal caliber (shape) is evaluated.
Uterine Contour (physical characteristics of the uterus):

Depending on a woman’s symptoms, the uterus may be evaluated by transvaginal ultrasound to look for fibroids or other anatomic abnormalities. If suspicion exists that the fibroids may be entering the endometrial cavity, a sonohystogram (SHG) or hysteroscopy (HSC) may be performed to further evaluate the uterine environment.
Source: CDC

Female fertility is known to decline with—

Age. Many women are waiting until their 30s and 40s to have children. In fact, about 20% of women in the United States now have their first child after age 35, and this leads to age becoming a growing cause of fertility problems. About one-third of couples in which the woman is older than 35 years have fertility problems. Aging not only decreases a woman’s chances of having a baby but also increases her chances of miscarriage and of having a child with a genetic abnormality.
Aging decreases a woman’s chances of having a baby in the following ways—
Her ovaries become less able to release eggs.
She has a smaller number of eggs left.
Her eggs are not as healthy.
She is more likely to have health conditions that can cause fertility problems.
She is more likely to have a miscarriage.
Smoking.
Excessive alcohol use.
Extreme weight gain or loss.
Excessive physical or emotional stress that results in amenorrhea (absent periods).
Source: CDC

We will begin by collecting a medical and sexual history from both partners. The initial evaluation usually includes a semen analysis, a tubal evaluation, and ovarian reserve testing.

Source: CDC

Infertility can be treated with medicine, surgery, intra-uterine insemination, or assisted reproductive technology. Many times these treatments are combined. Doctors recommend specific treatments for infertility based on—

The factors contributing to the infertility.
The duration of the infertility.
The age of the female.
The couple’s treatment preference after counseling about success rates, risks, and benefits of each treatment option.
Source: CDC