Infertility is defined as the inability to conceive a pregnancy after one year of unprotected intercourse. This definition of infertility is useful as a starting guide but must be modified to accommodate what we have learned through the IVF infertility treatment.
In an average population of women of childbearing age, approximately 20-25% will achieve pregnancy in a given month. In other words, if one hundred women attempt pregnancy in month one, we would expect that 25 would conceive. If the remaining 75 women attempted to conceive in month two, 25% of them or 18.75 will conceive in that month. If you continue this process, you will find that after one year about 95% of the original group will have conceived. This is how we have come up with the definition of female infertility. It is a statistical definition.
However, older women have a lower chance to conceive in any given month compared to younger women. It would take a group of older women a longer period of time to get to the point when 95% had conceived. In other words, if a group of women has a 12% chance of conceiving in a given month, it would take about two years for 95% to conceive.
It would be unreasonable to make older women wait that long because their fertility will continue to decline as they get older. We need to be more aggressive about starting fertility treatment in older women. Many infertility specialists, myself included, believe women who are 37 years old or older should initiate an infertility evaluation treatment after 6 months instead of a year.
The definition of infertility also needs to be modified based on the ability to deliver a baby not just become pregnant. Some women are able to conceive but have recurrent miscarriages. A woman who takes eight months to conceive and then has a miscarriage does not start over counting the next month as one month of trying.
Finally, the underlying infertility cause needs to be considered. For example a woman who has both of her fallopian tubes blocked does not need to have intercourse for a year to “prove” she is infertile. The same is true for women who do not ovulate. In these women, the infertility cause can be diagnosed immediately.
Infertility versus sub-fertility
Infertility is really a misnomer. Most of the patients we see are capable of conceiving a pregnancy, they just haven’t achieved a pregnancy as quickly as they would like. A better term for these couples is sub-fertility. This means that given a long enough period of time, these couples would eventually conceive without medical assistance.
Make no mistake; these are just semantics. Whether you call it sub-fertility or infertility, couples who have not been able to have a child have very real suffering due to this problem and should be treated the same way as patients with any other type of chronic disease. They should seek the help of an infertility specialist.
How common is female infertility?
Numerous estimates of the number of infertile couples have been published. In the United States, the survey from the National Center for Health Statistics reported that 10.5% of women in the reproductive age group were infertile. Unfortunately, only about one in five of these couples seek medical assistance for their problem.
Causes of infertility
Couples are always interested to know how often the male is “the one to blame” versus the female or both. There is no universal answer to this question. Depending on the patient population studied, you will see different contributions from different causes. For example, in older women, there is going to be a higher incidence of ovarian dysfunction. Younger women are more likely to have unexplained infertility. Estimates for the contribution of male factor range from 10-50%. Actually, there are probably multiple causes for infertility for most couples. Some causes for infertility may be hard to detect or currently unknown.