An unexplained infertility is diagnosed in 15–30% among the infertile couples after general fertility tests. These couples cannot achieve pregnancy due to an accident or undiscovered reasons, including dysfunction of oviduct with tubal patency, failure of fertilization, and implantation failure without organic lesion.
If the period of infertility is 2 years longer, patients have a high risk of infertility. It is difficult to unsolve the reasons for infertility by timed intercourse or intrauterine insemination (IUI). Therefore, active infertility treatment, including in vitro fertilization (IVF), should be advised.
In humans, pregnancy requires achieving a variety of the processes, such as encounter of the sperm and egg, fertilization, embryo development and a high-grade embryo implantation to a receptive endometrium. Fertility can be estimated using monthly fertility rate, that is, probability of achieving pregnancy during one menstrual cycle.
An average monthly fertility in a human is extremely low, at 20% only. Thus, the potential cumulative pregnancy rate for normally fertile couples is about 70-80%, 90-95%, and 100% at 6, 12, and 24 months, respectively. Infertility in one of seven couples is defined as inability to achieve pregnancy after 1 year of regular unprotected sexual intercourse. The causes of infertility are diverse, including abnormal sperm, impaired ovulation, occlusion or damage of the fallopian tubes, and endometriosis.
An unexplained infertility is diagnosed as detecting of no causes of infertility in about 15-30% of these couples after general fertility tests, including hysterosalpingography, confirmation of ovulation, serum anti-Müllerian hormone level as ovarian reserve, postcoital testing, and sperm testing. Female fertility also decreases with age increasing. Thus, some infertile women of late reproductive age may not conceive by chance, but patients with an unexplained infertility cannot achieve pregnancy due to undetected causes of infertility after performing general fertility tests.
Possible undetectable causes of infertility are spermatozoa disruption at uterotubal junction, tubal gamete disorder and embryo transport, tube fimbria dysfunction of oocyte retrieval, fertilization failure, impaired embryo development and implantation failure. In any case, patients with an unexplained infertility cannot become pregnant due to undetectable causes affecting the processes of spermatozoa or implantation between embryo and endometrium. Thus, they cannot greatly benefit from general treatment of infertility, including timely intercourse or IUI.
If a woman with an unexplained infertility is young and cannot achieve pregnancy within 2 years or less, she may not achieve pregnancy by accident. Thus, general infertility treatment is recommended. If the period of infertility is 2 years longer, patients have a high probability of undetectable factor of infertility. Causes of infertility are not solved by timed intercourse or IUI. Thus, it is recommended to use assisted reproductive technology (ART), including IVF.
Gynecologists should not repeat timed intercourse or IUI during the treatment of infertility in patients without identified causes of infertility. They should explain of why patients could not conceive and discuss active treatment of infertility, including ART. Causes of an unexplained infertility are often found during ART treatment.
Some cases of an unexplained infertility are unsolvable, even if couples start ART. In subsequent blog posts, we will discuss an unexplained infertility in details. We hope that our readers will improve their knowledge about an unexplained infertility and use the best treatment for infertility.