Standard infertility testing may not always uncover the cause. Approximately 10% of all cases of infertility are deemed “unexplained infertility” or “idiopathic infertility.”
Standard Infertility Testing
Standard infertility testing varies from clinic to clinic, but many components of testing are the same everywhere. Unexplained infertility affects 50% of infertility couples with a female partner under 35 years of age, and about 80% of couples with a female partner age 40 years and older. The cause may be something simple, but standard tests cannot determine it.
One likely cause of unexplained infertility is advancing age of the female partner. The egg reserve declines after age 35 years, and infertility is greatly increased for women age 38 years and older. The factors involved are poor egg quality and low egg quantity. Because egg factor infertility is not a commonly used category, these couples get placed in the unexplained infertility category.
Endometriosis is a medical condition where tissue that should only line the uterus (endometrium or endometrial tissue) grows in other places. Common sites for endometrial implants (tissue growths) include the fallopian tubes, ovaries, rectum, vagina, and outside of the uterus. Many experts consider infertility associated with mild endometriosis to be unexplained infertility. The cause and effect relationship is difficult to establish with endometriosis.
Principles of Treatment
The two main principles for treating unexplained infertility are:
• Increasing the number of eggs by using fertility medications. Each egg that develops and is released has an independent chance of being fertilized. If two or more eggs are produced in one cycle, the chance of conception increases.
• Place the egg and sperm close to each other, either with artificial insemination or in vitro fertilization. After the man ejaculates, millions of sperm are deposited near the cervix. However, very few of these sperm can reach the egg. By placing more sperm near the eggs, and using fertility drugs, the odds for pregnancy increase.
Ovarian Stimulation and Intrauterine Insemination (IUI)
Intrauterine insemination involves placing a washed, concentrated sperm specimen from the male partner into the female partner’s uterus using a small tube. Before the procedure, the woman takes medications to stimulate the ovaries to produce multiple eggs. This increases the chances of ovulation and pregnancy.
In Vitro Fertilization (IVF)
Many couples with unexplained infertility have good success with in vitro fertilization. When the couple fail after 2-3 trials of IUI, IVF is recommended. With this procedure, special techniques can be employed to assist with the process. Intracytoplasmic sperm injection (ICSI) involves directly placing a sperm inside of the egg. The egg and sperm are combined in the laboratory, and an embryo is formed. For some couples, the embryo cannot break free of the zonapellucida (shell around the egg), so assisted hatching helps. Assisted hatching involves making a tiny hole in the shell so the embryo can easily implant into the uterus lining.
For couples with unexplained infertility, the pregnancy success rate depends on the duration of the infertility. The longer the fertility issues have existed, the less likely the couple will be able to conceive without assistance. Pregnancy rates include:
• After five years of infertility, a couple with unexplained infertility have only a 1-2% chance of conceiving on their own.
• Treatment with IUI alone raises conception rate to 4%.
• Ovarian stimulation and IUI increases chances of pregnancy to around 5-8% per cycle.
• Treatment with gonadotropin injections and IUI raises conception rate to 17% per cycle.
• IVF has the highest success rate, with around 50% of couples achieving pregnancy.