Infertility is defined as the lack of pregnancy after one year of unprotected intercourse. The cause of infertility are: Male Factor (30%), Unexplained Infertility (25%), Ovulatory (20%), Tubal Peritoneal (20%), Uterine/Cervical (5%). Some of the main factors for infertility are as follows:

1) Advanced Maternal Age: There is a steady decline in fertility after the age of 35 years.

2) Paternal Age: There is decrease in semen volume and mobility with age.

3) Timing of Intercourse: The establishment of pregnancy is dependent on properly timed intercourse around the time of ovulation.

4) Other Factors that Impact on Fertility: 
a) Spermatotoxins: DBCP (Dibromocloropropane) pesticide, lead, bromine vapour, ethylene glycol
b) Smoking: Confirmed reproductive toxin
c) Caffeine
d) Alcohol
e) Stress & Anxiety

Life Style Changes Affecting Semen Parameters 
In upto 40% of infertile couples, the male plays a key a role for difficulty in conception. Infertility means failure to conceive after regular unprotected intercourse for one year.

According to WHO (2002), approximately one third of the world's male adult population smoke. Smoking exposes the spermatozoa to oxidative agents. 68% of smokers showed oligospermia and 63% showed asthenozoospermia. Tobacco contains some deadly toxic carcinogens, nicotine, carbon monoxide, nitrogen oxide and cadmium, which negatively affect male and female gametes and embryo. Tobacco chewing, which is very common in India, affects sperm parameters. Tobacco contains 30 mutagenic agents, of which nicotine is the most hazardous. It gets absorbed through skin, mucous membrane & respiratory tract and gets metabolised in the liver. The metabolised products get deposited in the semen, saliva, milk and seminal plasma which affect the sperm plasma membrane, causing infertility by their powerful oxidising action.

Alcohol consumption decreases the spermatogenesis, interferes with the production of GnRH, FTH, LH and testosterone. It also impairs the function of leydig cells and sertoli cells in the testes. Oligoseprmia is much higher in alcoholics. 
Tuberculosis & Infertility
Genital tuberculosis causes irreparable damage to reproductive organs resulting in infertility. Its incidence varies from 0.69% in developed countries to as high as 19% in India. Genitourinary tuberculosis is responsible for 30% to 40% of all extra-pulmonary cases, and is second only to lymph nodal involvement, thereby accounting for the third most common form of extra-pulmonary tuberculosis. Although genital tuberculosis can happen at any age, females in the reproductive age group are most commonly affected with infertility being the most common manifestation. 
Chromosomal Anomalies
1) Recurrent Miscarriages: Couples with two or more miscarriages, have a 5-8% chance of having a balanced translation.

2) History of Down Syndrome: If a fist degree relative was diagnosed with Down Syndrome, then it should be ascertained whether the affected individual underwent chromosomal testing. Approximately 90% of cases of Down Syndrome are Trisomy 21, which is a sporadic event. The remaining 10% are a result of translocation

3) History of still birth and congenital anomalies.

4) Severe Male Factor Infertility: In males with azoospermia or severe oligospermia, there is a 5-15% chance of chromosomal anomalies.