There are many possible causes of infertility. Unfortunately, in about one-third of cases no cause is ever identified.
Causes of infertility in women
Ovulation disorders -problems with ovulation are the most common cause of infertility in women, experts say. Ovulation is the monthly release of an egg. In some cases the woman never releases eggs, while in others the woman does not release eggs during come cycles. Ovulation disorders can be due to:
Premature ovarian failure - the woman's ovaries stop working before she is 40.
PCOS (polycystic ovary syndrome) - the woman's ovaries function abnormally. She also has abnormally high levels of androgen. About 5% to 10% of women of reproductive age are affected to some degree. Also called Stein-Leventhal syndrome.
Hyperprolactinemia - if prolactin levels are high and the woman is not pregnant or breastfeeding, it may affect ovulation and fertility.
Poor egg quality - eggs that are damaged or develop genetic abnormalities cannot sustain a pregnancy. The older a woman is the higher the risk.
Overactive thyroid gland
Underactive thyroid gland
Some chronic conditions, such as AIDS or cancer.
Scientists discover gene that explains infertility - scientists from the University of Edinburgh reported in the Journal of Cell Science that they identified a gene that controls a vital process in the formation of healthy fertile eggs.
They say their breakthrough will help researchers better understand how cells divide during reproduction, which in turn will help explain low fertility and sterility.
This gene allows chromosomes to bunch up together. The authors believe that this huddling of chromosomes secures the healthy development and subsequent fertilization of an egg.
They analyzed hundreds of infertile Drosophila oocytes (fruit flies) and found that without the gene SRPK, the chromosomes do not huddle together. This gene exists in human cells.
The researchers said that "the absence of SRPK ultimately leads to sterility and low fertility".
Problems in the uterus or fallopian tubes
The egg travels from the ovary to the uterus (womb) where the fertilized egg grows. If there is something wrong in the uterus or the fallopian tubes the woman may not be able to conceive naturally. This may be due to:
Surgery - pelvic surgery can sometimes cause scarring or damage to the fallopian tubes. Cervical surgery can sometimes cause scarring or shortening of the cervix. The cervix is the neck of the uterus.
Submucosal fibroids - benign or non-cancerous tumors found in the muscular wall of the uterus, occurring in 30% to 40% of women of childbearing age. They may interfere with implantation. They can also block the fallopian tube, preventing sperm from fertilizing the egg. Large submucosal uterine fibroids may make the uterus' cavity bigger, increasing the distance the sperm has to travel.
Endometriosis - cells that are normally found within the lining of the uterus start growing elsewhere in the body.
Previous sterilization treatment - if a woman chose to have her fallopian tubes blocked. It is possible to reverse this process, but the chances of becoming fertile again are not high. However, an eight-year study showed tubal reversal surgery results in higher pregnancy and live birth rates and is less costly than IVF.
Medications - some drugs can affect the fertility of a woman. These include:
NSAIDs (non-steroidal anti-inflammatory drugs) - women who take aspirin or ibuprofen long-term may find it harder to conceive.
Chemotherapy - some medications used in chemotherapy can result in ovarian failure. In some cases, this side effect of chemotherapy may be permanent.
Radiotherapy - if radiation therapy was aimed near the womans reproductive organs there is a higher risk of fertility problems.
Illegal drugs - some women who take marijuana or cocaine may have fertility problems.
Causes of infertility in men
Semen - Semen is the milky fluid that a man's penis releases during orgasm. Semen consists of fluid and sperm. The fluid comes from the prostate gland, seminal vesicle and other sex glands. The sperm is produced in the testicles. During orgasm a man ejaculates (releases semen through the penis). The seminal fluid helps transport the sperm during ejaculation. The seminal fluid has sugar in it - sugar is an energy source for sperm.
Abnormal semen is responsible for about 75% of all cases of male infertility. Unfortunately, in many cases doctors never find out why. The following semen problems are possible:
Low sperm count (low concentration) - the man ejaculates a lower number of sperm, compared to other men. Sperm concentration should be 20 million sperm per milliliter of semen. If the count is under 10 million there is a low sperm concentration (subfertility).
No sperm - when the man ejaculates there is no sperm in the semen.
Low sperm mobility (motility) - the sperm cannot "swim" as well as it should.
Abnormal sperm - perhaps the sperm has an unusual shape, making it more difficult to move and fertilize an egg.
Sperm must be the right shape and able to travel rapidly and accurately towards the egg. If the sperm's morphology (structure) and motility (movement) are wrong it is less likely to be able to reach the egg and fertilize it.
The following may cause semen to be abnormal:
Overheating the testicles - frequent saunas, hot tubs, very hot baths, or working in extremely hot environments can raise the temperature of the testicles. Tight clothing may have the same effect on some people.
Ejaculation disorders - for some men it may be difficult to ejaculate properly. Men with retrograde ejaculation ejaculate semen into the bladder. If the ejaculatory ducts are blocked or obstructed the man may have a problem ejaculating appropriately.
Varicocele - this is a varicose vein in the scrotum that may cause the sperm to overheat.
Undescended testicle - one (or both) testicle fails to descend from the abdomen into the scrotum during fetal development. Sperm production is affected because the testicle is not in the scrotum and is at a higher temperature. Healthy sperm need to exist in a slightly lower-than-body temperature. That is why they are in the scrotum, and not inside the body.
Hypogonadism - testosterone deficiency can result in a disorder of the testicles.
Genetic abnormality - a man should have an X and Y chromosome. If he has two X chromosomes and one Y chromosome (Klinefelter's syndrome) there will be an abnormal development of the testicles, low testosterone, and a low sperm count (sometimes no sperm at all).
Mumps - this viral infection usually affects young children. However, if it occurs after puberty inflammation of the testicles may affect sperm production.
Hypospadias - the urethral opening is at the underside of the penis, instead of its tip. This abnormality is usually surgically corrected when the male is a baby. If it is not the sperm may find it harder to get to the female's cervix. Hypospadias occur in about 1 in every 500 newborn boys.
Cystic fibrosis - Cystic fibrosis is a chronic disease that affects organs such as the liver, lungs, pancreas, and intestines. It disrupts the body's salt balance, leaving too little salt and water on the outside of cells and causing the thin layer of mucus that usually keeps the lungs free of germs to become thick and sticky. This mucus is difficult to cough out, and it clogs the lungs and airways, leading to infections and damaged lungs. Males with cystic fibrosis commonly have a missing or obstructed vas deferens (tube connecting the testes to the urethra; it carries sperm from the epididymis to the ejaculatory duct and the urethra).
Radiotherapy - radiation therapy can impair sperm production. The severity usually depends on how near to the testicles the radiation was aimed.
Some diseases - the following diseases and conditions are sometimes linked to lower fertility in males:
Sulfasalazine - this anti-inflammatory drug can significantly lower a man's sperm count. The drug is often prescribed for patients with Crohn's disease or rheumatoid arthritis. Usually this side effect goes away after the patient stops taking the medication.
Anabolic steroids - often taken by bodybuilders and athletes; anabolic steroids, especially after long term use can seriously reduce sperm count and mobility.
Chemotherapy - some medicines may significantly reduce sperm count.
Illegal drugs - consumption of marijuana and cocaine can lower a man's sperm count.