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  • Writer's pictureDr Anupa Nandi

What is unexplained infertility?

What is unexplained infertility?

Unexplained infertility is diagnosed if a couple fails to conceive after 1 year of regular unprotected sexual intercourse, and investigations confirm ovulation, patent fallopian tubes and normal sperm parameters. In some couples, unexplained infertility may result from subtle undetectable factors; while in other couples there may be a genuine absence of any abnormality. Even the most sophisticated investigations cannot identify all the potential contributory factors.

What are the chances of conceiving naturally?

It is known that over 80% of couples in the general population will conceive within 1 year if:

the woman is aged under 40 years and they do not use contraception and have regular sexual intercourse (every 2-3 days)

Of those who do not conceive in the first year, many will do so in the second year.

Therefore 90% of couples in the general population should fall pregnant within 2 years of trying.

In 30-40% cases, no cause can be identified, which is known as “unexplained infertility”.

What are the potential contributing factors?

There are various potential contributing factors that can be responsible for infertility. Some of these can be identified with testing and improved with treatment, however, others cannot.

Low ovarian reserve

Women are born with all their available eggs. Over time, with each menstrual cycle, the number of available eggs reduces. The rate of decline varies from one woman to another, and this loss is accelerated from the late 30’s- 40. Ovarian reserve refers to the number of eggs remaining in the ovaries at any given time. Ovarian reserve is related to the ability of the ovaries to respond to hormonal stimulation, but not predict the likelihood of natural conception. Natural conception can still occur with a low ovarian reserve.

Increased age (over 35 years) and low oocyte (egg) quality

It is known that the best predictor of egg quality is age. With declining quality of eggs with age, their potential to be fertilised is diminished. The embryos created with these eggs could have altered chromosomal content, which often makes the embryo unable to implant or increases its risks of miscarriage.

Lifestyle factors

Smoking, alcohol intake and being overweight, can have an impact on fertility, by affecting the quality of eggs and sperms.

Tubal function defects

The fallopian tubes may seem to be open during investigations, however, the mechanism to move the egg along the tube to the womb might not be working properly. There is, unfortunately, no test available for this. Subtle tubal function defects could lead to unexplained infertility in an otherwise patent tube.

Fertilisation defects

There may be problems with the mechanism the sperm has to fertilise the egg. The fertilisation defects could be revealed during an IVF cycle.

Implantation defects

There may be problems preventing the fertilised embryo from implanting into the lining of the womb.

Metabolic disorders, immunological and genetic factors

There may be known or unknown medical or genetic problems with one or both partners that are playing a role in infertility.


This is a chronic disorder in the woman, which causes painful periods. It can be diagnosed with a keyhole surgery (laparoscopy) if there are symptoms suggestive of endometriosis. Endometriosis is found in a significant proportion of women with infertility and is known to play a role.


Fibroids are benign growths of muscle within the layers of the uterus. In some cases, these can distort the womb lining and cause infertility.


Adenomyosis is a condition that can cause painful, heavy periods, and can also contribute to infertility.

What investigations can be done?

Unexplained infertility is a diagnosis of exclusion. Some tests of common causes of infertility should be carried out on both partners. These may include:

Detection of ovulation:

If a woman is having regular periods, it is likely that she is ovulating each month; however, there are some tests that can help confirm this:

A urine test looking for luteinizing hormone surge, which suggests impending ovulation. A blood test on day 21 of the cycle to check rising progesterone levels in a regular 28 days cycle. Ultrasound monitoring of the follicles (which contain eggs) and confirmation of the rupture of the follicle after ovulation.

Tubal patency testing:

These are tests to see if the fallopian tubes are open or if they have been blocked (due to infection and scarring):

Hysterosalpingogram (HSG) - this is an x-ray where a contrast dye is passed through the neck of the womb and into the fallopian tubes to confirm that the tubes are open by demonstrating the flow of dye out through the tubes.

Hysterocontrast sonosalpingography (HyCoSy) - this is a similar test to an HSG except that this is done with ultrasound scanning rather than an x-ray.

Laparoscopy and dye test – this is a keyhole surgery, where dye is passed through the fallopian tubes and spill of the dye can be seen with a camera inserted through the navel.

Semen analysis:

A semen sample is analysed to check for the normal number, appearance and motility. However, routine semen analysis does not detect sperm function defect.

Pelvic ultrasound and saline infusion sonography:

An ultrasound scan can be used to assess the inside of the womb.

Ovarian reserve testing:

Blood tests and/or ultrasound scan to assess for a satisfactory reserve of eggs in the ovaries. It cannot predict the chances of natural conception. This is usually done as a workup for assisted conception treatment like IVF.

Laparoscopy in symptomatic women:

This is keyhole surgery to look for disorders such as endometriosis. As this is an invasive test, it is reserved only for women who have symptoms suggesting the possibility of endometriosis such as painful periods, pain during intercourse.


A small camera inserted through the neck of the womb to assess the inside of the uterus. It is only performed if ultrasound scan detects any intrauterine conditions such as septum, polyp, fibroid or unusually thin endometrium suggesting the possibility of scarring inside the uterus.

Written by Dr Anupa Nandi

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