Unexplained infertility simply means we do not know why the couple is infertile – it is a confession of medical ignorance. Patients with unexplained infertility fall into two groups. One is the group who really have no infertility problem whatsoever, but are just plain “unlucky”. The other is the group which do have a reason for their infertility – but the reason is so subtle, that with present-day medical technology, we cannot find it.
Infertility may be said to be ‘unexplained’ if the woman is ovulating regularly, has open fallopian tubes with no adhesions or endometriosis ; if the man has normal sperm production; and the postcoital test is positive. Intercourse must take place frequently, particularly around the time of ovulation, and the couple must have been trying to conceive for at least one year.
Using these criteria, about 10% of all infertile couples have unexplained infertility. However, the percentage of couples classified as having unexplained infertility will depend upon the thoroughness of testing; and the sophistication of medical technology.
Possible causes of unexplained infertility
It is possible that there may be a subtle defect in the mechanism by which the fimbria “pick up” the egg at ovulation; or the cilia in the tube may not function properly.
It would appear that a very small number of cases of unexplained infertility are due to the persistent production of abnormal eggs. These may have a deformed structure or chromosomal abnormalities.
In some cases it would appear that eggs are produced, and mature correctly within the follicle which then goes on to become a corpus luteum without however first bursting to release the egg. The egg is therefore effectively ‘trapped’ inside the unbroken corpus luteum – called a luteinized unruptured follicle (LUF) syndrome.
Luteal phase abnormalities:
The luteal phase is the part of the cycle that follows after the egg has been released from the ovary. It may be inadequate in one way – and this is called a luteal phase defect.
The corpus luteum produces the hormone called progesterone. Progesterone is essential for preparing the endometrium to receive the fertilized egg. Several things can go wrong with progesterone production: the rise in output can be too slow, the level can be too low, or the length of time over which it is produced can be too short. Another possibility is a defective endometrium that does not respond properly to the progesterone.
Luteal phase defects can be investigated either by a properly timed endometrial biopsy; or by monitoring the progesterone output by taking a number of blood samples on different days after ovulation and measuring the progesterone level in them.This used to be a very popular diagnosis many years ago, but most doctors today believe that this condition is overdiagnosed and overtreated.
The immune system can react against the man’s sperm, and kill them, immobilize them or make them stick together. Women can also develop an immune reaction to the coating of their own eggs, which can prevent sperm from attaching to them.Some doctors also believe that a woman’s immune system can prevent her embryos from implanting. However, these “causes” are highly speculative and unproven.
Certain infections have been shown to be responsible for some cases of unexplained infertility. For example, mycoplasma or chlamydia may be present in numbers that are not enough to show up in a clinical examination, but which nevertheless cause infertility. This is why some doctors use empiric therapy with antibiotics.
Inability of sperm to penetrate eggs:
Some men have a completely normal sperm count, but their sperm cannot fertilize the egg. The only way to make this diagnosis is by IVF; if donor sperm can fertilize the eggs; but the husband’s sperm fail to do so, then the diagnosis is confirmed.
Some women have an abnormal endometrium ( uterine lining) which does not allow the embryo to implant . This is a subtle finding, which is often missed. It can be diagnosed by doing serial vaginal ultrasound scans, to assess the thickness and texture of the endometrium. In some infertile women, the endometrium remains persistently thin. This may be because of inadequate uterine blood flow, or poor estrogen receptors in the endometrial cells. This can be a difficult problem to treat, and therapy is usually empirical ( either low-dose aspirin or high doses of estrogen).
Studies on infertile groups of men and women have produced contradictory findings about the importance of psychological factors in causing infertility. We believe that it is not the stress which causes infertility, it is the infertility which causes the stress !