It is commonly understood as state of not being able to get pregnant even after trying for a year or two is called infertility.

Let us first understand what pregnancy is. This should help one understand what infertility is. Pregnancy is a 3 step process-

1. Ovulation:Women release egg, which travels to fallopian tube. Either of two things can happen there. A sperm can penetrate it within 24 hours or it degenerates.
2. Fertilization:sperms released by men meet an egg and penetrate it.
3. Implantation:The fertilized egg goes to the uterus through the fallopian tube where it attaches to the inside wall of the uterus, also called endometrium.

Infertility is a state where any of these three steps are not working as expected.

Here are some of the common causes of infertility-

1. Endometriosis:Usually the chances of developing endometriosis are higher for women who have family history of this disease. In this case, tissue similar to that of the lining of the uterus grows outside the uterus and can possibly damage ovaries, uterus and fallopian tubes. Endometriosis is the most common known cause of infertility. Doctors usually do laparoscopy to confirm its presence.
2. Ovulation related problems:This is the 2nd most common cause for infertility among women. Absence or infrequent and light menstruation is frequently observed symptom of ovulation related problems. Various lifestyle and environmental factors such as physical or emotional stress, excessive medications, etc. also lead to ovulation related problems. Chances of cure are high in this case. It is important that the doctor that identifies actual cause in order to suggest right treatment.
3. Consumption of Tobacco or other such products with nicotine:It is believed that women who smoke are 60% more likely to have infertility related issues as against those who do not smoke. Therefore it is better to be avoided when one has decided to conceive.
4. Age:Did you always wonder how will age affect pregnancy. It has again to do with the ovulation. The quality of eggs released goes down with age. Therefore chances of fertilization when a sperm meets an egg become less. 30 is the magic number that everyone speaks of. But the quality of eggs continues to go down with age. Therefore the longer you delay greater would be the chances of issue with pregnancy.
5. Polycystic ovarian syndrome (PCOS):It is a hormonal problem. Most women with this condition have many small cysts in their ovaries. It is important to note that having cysts in their ovaries does not mean one is suffering from PCOS. Cysts in the ovaries can be present for variety of reasons. It is believed that 5% to 10% of women are diagnosed with polycystic ovarian syndrome and is one of the common cause of infertility in women. Menstrual disorders are commonly observed among women with this condition. Contraceptive pills are usually recommended by doctors for treatment of PCOS. Birth control pills contain estrogen and progesterone which helps in bringing hormonal balance in women. This in turn regularizes menstrual cycle of women.
6. Sperm disorders:While it has been debatable, low sperm count is one of most common cause of infertility among men. Abnormally shaped sperms can also cause infertility. Surgery is the most commonly suggested treatment for such condition.
7. Blockage in sperm carrying tubes:Any type of obstruction during sperm movement before ejaculation can also lead to reduced sperm counts. This even causes diseases such as Chlamydia and gonorrhoea. Some men have congenital (since birth) absence of the vas deferens on one or both sides. Vas deferens is the tube through which seminal vesicles, prostate gland and the bulbourethral glands, which largely constitute semen, are transmitted.