About 40% of all cases of
infertility are due to problems with the female partner and another 30% are due to
problems in the male partner. The rest of the remaining 30% of cases are due either to a cause which affects both the partners, or to a cause which cannot be identified.
A good knowledge of the female reproductive organs, and how pregnancy occurs helps in understanding the different causes of female infertility.
For a pregnancy to occur, three things are vital. There are other issues involved, but these 3 are the most important:
- Ovulation: A woman mustovulate (produces an egg from her ovary) regularly, usually at about the 14 -16th day in a normal menstrual cycle of 28 -30 days.
- Patent Genital tract: The female genital tract has to be open and free of any obstructions so that the sperm can reach the egg.
- Adequate Male sperm: The male partner needs to have adequate sperms in his semen for pregnancy to occur.
So, if the couple cannot conceive and suffers from infertility, there has to be one of these problems:
- Anovulation: Failure to produce an ovum.
- Obstruction in the Genital tract: Any obstruction in the genital tract - either in the fallopian tubes or in the uterus or in the cervix or in the vagina - can prevent the sperm from reaching the egg.
- Inadequate Male sperm: The male partner must have adequate number of sperms in his semen to be able to cause a pregnancy.
CAUSES OF FEMALE INFERTILITY
The main causes of female infertility are Anovulation and Obstruction in the genital tract.
A. Causes of Anovulation
This is the commonest cause of female infertility, accounting for 40% of all causes. It is unlikely in women who are menstruating regularly but is not uncommon.
- Age: There is a steady decline in the rate of ovulation after the age of 35 years. The rate of ovulation and successful pregnancy at the age of 40 years is almost half that at the age of 20 years.
- Polycystic Ovarian Disease (PCOD): This cause of female infertility was identified only about twenty years ago. PCOD is a condition characterised by a number of cysts in the ovaries and a grossly reduced ovulation rate. Ovulation may be irregular and not occur in every month. In severe cases of PCOD, ovulation may stop altogether. There is also associated hormonal imbalance with a high level of hormones like insulin and androgen in this condition.
- Defects in the endocrine glands: Glands like the thyroid and the pituitary glands are active participants in maintaining normal female fertility . Both hypo - and hyperthyroidism can cause anovulation. High levels of prolactin secreted by the pituitary is also an indicator of irregular ovulation. A high insulin level is frequently associated with PCOD. Pituitary insufficiency, for example, as in Sheehan's Syndrome, can not only cause anovulation but also amenorrhea (loss of periods).
- Endometriosis: Endometriosis is a condition where bits of the endometrium (inner uterine lining) grows in places other than inside the uterus. If this growth occurs on the ovary, it can cause anovulation and cause female infertility.
- Ovarian Infections / tumours: Both infections and tumors can not only physically block ovulation but can also cause hormonal imbalance leading to anovulation.
- Leutenized unruptured Follicles: This is a relatively uncommon cause of female infertility. In this condition, the graaffian follicles develop normally, but fail to rupture - usually because of a lack of stimulus by a low LH level.
- Subclinical Adrenal Cortex Failure: The hormones of the adrenal cortex is closely linked to the reproductive process. So any problem with these hormones - either a low level or a high level - can cause anovulation.
- Sex Chromosome defects: Sex chromosomal defects like XXY, XXXY, XYY etc can cause anovulation.
B. Obstruction in the Genital Tract
About one third of all causes of female infertility is due to obstruction in the genital tract. Obstruction can occur anywhere in the genital tract - the tubes, the uterus, the cervix or the vagina. Adhesions or scar tissue in the pelvis around the tubes can also cause obstruction, and prevent the sperm from reaching the ovum to fertilize it. Adhesions inside the uterus can be seen in a conditon known as Asherman's syndrome.
Tubal Obstructions – Tubal obstructions may be total or partial and may account for 20% of all causes of female infertility. Endometriosis and pelvic inflammatory diseases, usually as a result of chlamydia infection are common culprits. Some important causes of tubal obstruction are :
- Previous infections of the tubes: Infections can occur due to abortions or previous childbirth. Common infecting organisms are S. aureas and S. pyogenes. A very common infection is by the chlamydia trachomatis organism which causes no specific symptoms at the time of infection, but the damage it causes to the tubes are discovered only on investigating for infertility.
- Infections of the genital organs by N. gonorrhoea, chlamydia trachomatis, syphilis or M. tuberculosis are common causes of infertility in women.
- Congenital Absence of the tubes from birth usually as a result of sex chromosomal defect.
Pelvic Adhesions – Adhesions are scar tissues formed as a result of previous infections and may affect the tubes at different regions. They are a common effect of endometriosis.
- Fimbrial Adhesions: Adhesions near the fimbria of the tube (part of the tube near the ovaries) may pull the tube out of its proper position and prevent ‘picking up’ of the ovum by the tube. This is a common cause of female infertility identified during investigation.
- Peritubal adhesions: Strands of adhesions may create a mechanical barrier between the tube and the ovary.
- Buried ovary: The ovary may be completely or partially buried in dense adhesions preventing ovulation or ovum pickup.
Uterine Factors - Certain conditions in the uterus may affect
fertilization and
implantation of the ovum and contribute to female infertility.
- Absence of the uterus: from birth or by surgery.
- Atrophy: or small size of the uterus, insufficient to support pregnancy, usually a result of surgery on the uterus or radiation.
- Uterine synechia: Synechia are adhesions inside the uterus causing the two walls of the uterus to fuse together, totally or partially, thus obliterating the endometrial cavity. This is commonly seen in infertility due to Asherman's Syndrome.
- Uterine tumours: Certain uterine tumours like fibroids may block the tubal opening, or prevent implantation of the fertilized ovum.
Cervical Factors - Cervical factors may affect the upward movement of the sperm and prevent pregnancy.
- Poor cervical mucous – The cervical mucous may be thick and impenetrable due to low oestrogenic stimulation. This will act as a barrier or obstruction to the sperm. Acidic mucous or the presence of antisperm antibodies in the mucous can also prevent ascent of the sperm.
- Loss of cervical mucous: due to surgery and amputation of the cervix, or excessive cervical diathermy.
- Faulty direction of the cervix: The cervix normally faces into the posterior vaginal vault where the sperm tends to pool. In some patients, the position of the cervix may be abnormal due to faulty direction of the uterus (retroversion), uterine prolapse or cochleate uterus. This is a very unlikely cause of female infertility .
- Cervical Tumors: Tumors like polyps or cervical fibroids can block the cervical canal.
Vaginal Factors :
- Vaginal tumours
- Vaginal septa: Vaginal septa or membranes can cause a mechanical barrier to the sperm.
- Vaginal infection with purulent pus: Infections such as by the trichomonas organism is believed to cause infertility. But this is still under research and has not been proved conclusively.
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