Infertility is not being able to get pregnant after one year of having unprotected sex. Women who do not have regular menstrual cycles, or are older than 35 years and have not conceived during at least a one-year period of trying, should consider making an appointment with an infertility specialist.

To conceive;

A woman’s body must release an egg from one of her ovaries during ovulation.
A man’s sperm must join with the egg along the way, a process called fertilization.
The fertilized egg must go through a fallopian tube toward the uterus (womb).
The fertilized egg must get implanted to the inside of the uterus
About 6% of married women aged 15-44 years in the United States are unable to conceive after one year of unprotected sex (infertility).

Also, about 12% of women 15-44 years of age in the United States have difficulty in conceiving or carrying a pregnancy to term, regardless of marital status.

A woman is not always responsible for infertility, both men and women contribute to infertility.

Many couples struggle with sterility 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%)

Causes of infertility in men

Infertility in men can be caused by different factors and is normally 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 infertile. Instead, a semen analysis helps to establish 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 scorch. The heat may in turn affect the concentration or morphology of the sperm.
Medical conditions or exposures such as infection, testicular failure, diabetes, cystic fibrosis, trauma, or treatment with chemotherapy or radiation.
Unhealthy habits such as smoking, heavy alcohol use, testosterone supplementation, steroid use, and illicit drug use.
Environmental toxins including exposure to lead and pesticides.
Causes infertility in women

Women need functioning ovaries, fallopian tubes, and a uterus in order to conceive. Conditions affecting any one of these organs can contribute to female infertility.

Ovulation: Regular 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 check 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 (anovulation). This may be because of several conditions and needs an evaluation by a doctor. Potential causes of anovulation include the following:
Polycystic ovary syndrome (PCOS). PCOS is the most common cause of female infertility. It is a hormone imbalance problem that can interfere with normal ovulation.
Functional hypothalamic amenorrhea (FHA). FHA relates to excessive physical oremotional 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 surgical, congenital, medical, or unexplained causes. Ovarian reserves declines with age.
Premature ovarian insufficiency (POI). POI occurs when a woman’s ovaries fail before she is 40 years of age.
Menopause: This is an age-appropriate decline in ovarian function that usually occurs around age 50. It is often associated with hot-flashes and irregular periods.
It is important to note:

Ovarian function. Several tests exist to evaluate a woman’s ovarian function.
No single test is a perfect predictor of fertility.
The 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.
Things that increase a woman’s risk of infertility

Female fertility is known to decline with;

Age: Ageing decreases a woman’s chances of having a baby as well as increases her chances of miscarriage. About 20% of women in the United States now wait until their 30s and 40s have their first child 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 issues. 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
She is more likely to have miscarriage
She is more likely to have health conditions that can cause fertility problems
Her eggs are not that healthy
Smoking
Excessive intake of alcohol
Extreme weight gain or loss
Excessive physical or emotional stress that results in amenorrhea (absent periods)
Some medicines used to treat infertility in women

Some common medicines used to treat infertility in women include –

Clomiphene citrate (Clomid®*) is a medicine that causes ovulation by acting on the pituitary gland. It is often used in women who have polycystic ovarian syndrome (PCOS) or other problems with ovulation. This medicine is taken by mouth.
Human menopausal gonadotropin or hMG (Repronex®*; Pergonal®*) are medicines often used for women who don’t ovulate because of problems with their pituitary gland-hMG acts on the ovaries to fuel ovulation. It is an injected medicine.
Follicle-stimulating hormone or FSH (Gonal-F®*; Follistim®*) are medicines that are usually injected, it work much like hMG. It triggers the ovaries to begin the process of ovulation.
Gonadotropin-releasing hormone (Gn-RH) analog are medicines often used for women who don’t ovulate regularly each month. Women who ovulate before the egg is ready can also use these medicines. Gn-RH analogs act on the pituitary gland to change when the body ovulates. These medicines are usually injected or given with a nasal spray.
Metformin (Glucophage®*) is a medicine doctors use for women who have resistance and/or PCOS. This drug helps lower the high levels of male hormones in women with these conditions. This helps the body to ovulate. Sometimes clomiphene citrate or FSH is combined with metformin. This medicine is usually taken orally.
Bromocriptine (Parlodel®*) is a medicine used for women with ovulation challenges because of high levels of prolactin. Prolactin is a hormone that causes production of milk.
*Note: Use of trade names and commercial sources is for identification only and does not imply endorsement by the U.S. Department of Health and Human Services.

Many fertility drugs increase a woman’s chance of having twins, triplets, or other multiples. Women who are pregnant with multiple fetuses have more problems during pregnancy.

Source: http://healthdiary365.com/2017/10/14/infertility-in-men-and-women-causes-and-treatment/