About one in seven couples in developed countries and one in 10 couples in developing countries (10%) 1 experience infertility (not becoming pregnant after about a year of trying). Although the term infertility is commonly used, for most people the more accurate term is subfertility, as relatively few people are totally infertile.
In Spain and Sweden, Germany and Greece, the total fertility rate--or the average number of children that a woman based on current indicators, is expected to give birth to--was 1.4 or lower last year, according to the World Health Organization ... In no west European country did the rate reach 2.1--the marker that, demographers say, means an exact replenishment of the population. By contrast, the United States had a 2.0 rate, which demographers attribute to greater immigration.
People with infertility may never have conceived a pregnancy to their knowledge (called primary infertility), but people who have had a baby before can also experience infertility (called secondary infertility).
For about three out of every four couples with problems conceiving (75%), discussion with a doctor and/or medical tests will show what is preventing pregnancy. The other couples who have not been able to conceive naturally, are said to have unexplained infertility (sometimes called idiopathic infertility). It does not mean there is no physical explanation for the infertility, but just that medical tests have not identified any specific problem. Sometimes, infertility simply remains a mystery, and there is just no way of knowing why one person becomes pregnant and another does not.
A quarter of infertility (25%) cannot be explained because:
Current tests are not perfect at finding all problems
The problem preventing pregnancy is not covered by the usual range of tests used for assessing fertility
There are causes which are not yet understood by scientists.
There are factors that might be affecting fertility for which no reliable test exists.
About 90% of fertile couples will conceive (become pregnant) within a year of regular unprotected sex, and another 5% will become pregnant in the second year. In the first three years of unexplained infertility, at least one in three couples will become pregnant. This means that even without any special actions or treatments (other than sexual intercourse at optimal times), the chance of pregnancy is still quite good . On average, a couple who have been infertile for more than three years, have a 1 or 2% chance of conceiving in a specific menstrual cycle if they are having regular unprotected sex without any fertility treatment.
Unexplained infertility (also called idiopathic infertility) cases are those in which standard infertility testing has not found a cause for the failure to conceive. The definition of what "standard testing" consists of is not agreed upon by all experts.
Various studies have reported that 0-26% of infertile couples have unexplained infertility. The most commonly reported figures are between 10-20% of infertile couples.
There are many small and big steps along the way to conception and establishing a pregnancy, and a problem at any of these points could be preventing conception or the establishment of pregnancy. These points are:
Healthy ova (eggs) being regularly released by the woman's ovaries (the process of ovulation)
Healthy sperm, contained in a man's semen (fluid ejaculated during sexual arousal), passing through the cervix (opening of the uterus) without being harmed by the woman's mucus (thick fluid), and moving up through the woman's uterus (womb) to meet the egg in the fallopian tubes, without being hindered by any chemical or substance that might damage the sperm
Hormones coming at the right times, in the right quantities, to trigger many of the mechanisms needed to keep the process functioning
Eggs moving freely through the woman's fallopian tube so they can join with healthy sperm
Sperm meeting the egg need to be able to fertilise that egg so that it can develop into an embryo, which can move into the womb, implant itself in the lining of the womb and begin to develop.
In reality, there are hundreds (thousands ??) of "causes" of infertility. What is meant by this is that there are a lot of things that have to happen perfectly in order to conceive and have a baby. As a simplified example:
The hormones that stimulate egg development must be made in the brain and released properly
The egg must be of sufficient quality and be chromosomally normal
The egg must develop to maturity
The brain must release a sufficient surge of the LH hormone to stimulate final maturation of the egg
The follicle (eggs develop in structures called follicles in the ovaries) must rupture and release the follicular fluid and the egg
The tube must "pick up" the egg
The sperm must survive their brief visit to the vagina, enter the cervical mucous, swim to the fallopian tube and "find" the egg
The sperm must be able to get through the cumulus cells around the egg and bind the shell (zona pellucida) of the egg
The sperm must undergo a biochemical reaction and release their DNA package (23 chromosomes) into the egg
The fertilized egg must be able to divide
The early embryo must continue to divide and develop normally
After 3 days, the tube should have transported the embryo into the uterus
The embryo must develop into a blastocyst
The blastocyst must hatch from its shell
The endometrial lining of the uterus must be properly developed and receptive
The hatched blastocyst must attach to the endometrial lining and "implant"
Many more miracles in early embryonic and fetal development must then follow...
A weak link anywhere in this chain can cause failure to conceive.
The above list is very oversimplified, but the point is made. There are literally hundreds of molecular and biochemical events that have to function properly in order to have a pregnancy develop. The standard tests for infertility barely scratch the surface and are really only looking for very obvious factors, such as blocked tubes, abnormal sperm counts, ovulation regularity, etc. These tests do not address the molecular issues at all. That is still for the future...
When a standard workup is unable to determine the cause of a couple's infertility, there are several possibilities still worth exploring.
The overall likelihood of pregnancy declines, however, with advancing female age. The unexplained infertility of a woman in her late 30s or early 40s may be explained, in many cases, by age. From a clinical standpoint, it is often useful to think of these cases as "age-associated infertility".
The likelihood of a diagnosis of unexplained infertility is increased substantially in women 35 and over - and greatly increased in women over 38. The reason for this is that there are more likely to be egg quality problems as women age. Since we do not have a "standard category" called egg factor infertility, these couples sometimes get lumped in to the "unexplained" infertility category.
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