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What are the causes of female infertility?

There are many different causes of female infertility. Sometimes more than one minor cause is present and collectively then is enough to create a problem.

The female reproductive tract consists of 2 ovaries, 2 fallopian tubes, a uterus (womb), cervix (neck of the womb) and vagina.

Causes of infertility in a woman may be divided according to the anatomical level at which the problem lies.  The sort of problems that may occur at each level is set out below:

Ovarian

Anovulation

Anovulation means the failure of the release of the egg from the ovary. Overall this is the most common cause of female fertility problems (40%). In ‘normal’ menstrual cycles hormones are released from the pituitary gland (in the brain), which induce follicular formation  which allows the egg to finish its development and eventually to mature. Once mature, the egg is released or ovulation occurs. In ‘normal’ circumstances one egg is released per month.

If an egg is not released, pregnancy cannot occur. There are a number of reasons why ovulation may not occur. The most common reason is the presence of polycystic ovaries (PCO), which are described below. Other hormone imbalances may be associated with a failure of ovulation such as hyperprolactinaemia or thyroid dysfunction. Extreme weight changes may be enough to stop ovulation. As women get older the ovaries may become more and more resistant to the hormone stimulation, which induces normal ovulation.

Polycystic Ovarian Syndrome (PCOS)

Polycystic ovarian syndrome is a condition in which there is a hormonal imbalance within the ovaries. It is a complex condition. In PCOS, the ovaries are bigger than average, and the outer surface of the ovary has an abnormally large number of smaller follicles. In PCO these follicles remain immature, which means that ovulation rarely happens and so the woman is less fertile.

What are the causes of female infertility?

Women who have PCOS may have the following problems:

  1. Infertility due to lack of ovulation,
  2. Excessive body hair growth (hirsutism) due to imbalance between hormones,
  3. Irregular menstrual cycles and heavy bleeding (cycles which are either less than 21 days or more than 35 days apart) due to lack of ovulation,
  4. Acne
  5. Obesity.

Some women with PCOS may have a higher than normal miscarriage rate if they become pregnant.

However, all of these symptoms are not present in all patients with polycystic ovaries. The condition represents a spectrum of problems. Regular cycles may occur in 40% of women with PCO. Many women with PCO have no additional hair growth and some women are underweight!

While it is not known if women are born with this condition, PCO seems to run in families. Ongoing research is trying to clarify whether there is a clearly identifiable gene for PCOS. Women are also at a risk when overweight. Maintaining weight or body mass index (BMI) below a critical threshold is probably very important as weight loss improves hormonal abnormalities and improves the likelihood of ovulation and thus pregnancy.

The diagnosis of PCOS is made primarily on the woman’s presenting history and examination. The diagnosis can be confirmed on ultrasound or by measuring the woman’s hormonal levels.

Because PCOS can lead to a resistance to insulin it has been shown that women with PCOS will respond better to fertility treatments if they are treated concurrently with Metformin ( a type of drug known as an “insulin-sensitising agent” which lowers the blood sugar level, in turn reducing the excessively high insulin). Studies suggest that it may well be useful in several areas: helping weight reduction, normalizing blood cholesterol and improving irregular periods (70%) leading to ovulation. The most common side effects during treatment on Metformin are diarrhoea, nausea, vomiting and abdominal bloating.

In very resistant cases of PCOS an operation called ovarian drilling, performed by laparoscopy, can also be used to treat women with PCOS. During this procedure the ovary is cauterized by drilling into it in a number of spots.

Tubal

Tubal factors account for 20% of explained causes of infertility. The fallopian tube is the road along which the sperm and egg usually meet. Either blockage of the pathway or impairment of the function of the tube can cause a woman to be infertile.

The function of the fallopian tubes is delicate. It is partially dependant on the close proximity of the tubes to the ovaries. But also dependent on the ability of the tube to move closer to the area on the ovary from which the egg will be released. The inside of the fallopian tubes contain tiny hairs or cilia, which by beating are able to suck the egg into the end of the tube and so “catch” the egg. The inside lumen of the tube must be open to allow the sperm to make their way down the tube to the egg. After fertilization the cilia are responsible for moving the embryo (which cannot move on its own) back up the tube to the uterus / womb.

Previous infection or inflammation of the fallopian tubes may damage both the ability of the tube to move due to the formation of scar tissue and also the ability of the cilia to beat or function. In addition, this damage may actually block the tube and thus prevent the sperm and the egg meeting at all! Infection is the most common cause of tubal factors. Infection may occur as a result of pelvic inflammatory disease (PID) but may also be secondary to other nearby infections such as appendicitis. Any procedure involving the inside of the womb such as a D&C, an endometrial biopsy, a termination of pregnancy etc, carries a risk of pelvic infection.

Tubal blockages may occur secondary to endometriosis (see below) or because or previous surgery. Ectopic pregnancy (a pregnancy that implants in the tube) will result in damage of the tube.

Very rarely congenital defects of fallopian tube formation occur. This may result in the absence of one or both fallopian tubes.

Uterine

Abnormalities of uterine anatomy or function may cause infertility. These may include leiomyomas (Fibroids), endometrial polyps, foreign bodies (e.g. an IUD), intrauterine synechiae (scar tissue), congenital malformations and chronic endometritis (infection).

It is felt that these conditions may cause a failure of implantation due to mechanical interference and/or a functional impairment of normal endometrial growth and maturation.

Fibroids

Fibroids are benign (non-cancerous) growths of the muscle of the uterus (womb).  They are sometimes called myomas, fibromyomas or leiomyomas, but most people call them fibroids.  Fibroids are common – around 20% of women get them. Fibroids can affect the shape and internal environment of the uterus.  They can make it more difficult to conceive but they only account for about 3% of the total cases of infertility.

Fibroids are most common in women in their 40s and 50s, towards the end of the reproductive years.  They are more common in women of Afro-Caribbean origin, who also tend to be affected at a younger age.

There are different types of fibroids, named according to where they are found:-

  • Intramural fibroids are found within the muscular wall of the uterus.
  • Subserosal fibroids grow outwards from the outside wall of the uterus. They can become very large.
  • Submucosal fibroids grow from the inner wall of the uterus and can take up space inside the uterus.  These account for only 5% of all fibroids.

Fibroids grow very slowly. They can cause symptoms as they grow bigger, but even so, at least half of all fibroids cause no problems at all. The most common symptom / sign of a fibroid is heavy periods.

Up to half of all women with fibroids have heavy periods.  In some cases this can lead to anaemia.

As fibroids get bigger they may cause pressure related symptoms such as lower abdominal discomfort or backache, or may press on the bladder causing symptoms such as needing to pass urine more often than normal.  The uterus may also press on the rectum causing constipation.  Some women experience pain or discomfort during sexual intercourse (dyspareunia) because of fibroids. The problems that fibroids may cause depend on their location.

It is estimated that fertility problems are one of the presenting features in about ¼ of women with fibroids.  There is a well-established relationship between the presence of fibroids and lower fertility.  When compared to other causes of infertility, however, they are a relatively uncommon cause, being implicated in only 3% of couples.  It may be that a delay in having children (whether voluntary or involuntary) predisposes to the development of fibroids and this is more often an association rather than a causative feature.

The diagnosis of fibroids is most accurately made by ultrasound (U/S). Whilst pelvic examination may flag the diagnosis U/S allows the fibroids to be characterised according to the size, number and type. By using techniques which allow the uterine cavity to be evaluated, such as SIS, HSG or hysteroscopy, it is possible to determine whether the fibroid(s) affect the cavity or internal lining of the uterus/womb. This is particularly important with respect to fertility. If the fibroid affects the cavity then it may be necessary to remove the fibroid prior to fertility treatment. On the other hand if the fibroid does not block a tube or affect the cavity there is no benefit to removing it.