To estimate the effects of aging on the percentage of outwardly healthy couples who are sterile (completely unable to conceive without assisted reproduction) or infertile (unable to conceive within a year of unprotected intercourse).
A prospective fecundability study was conducted in a sample of 782 couples recruited from 7 European centers for natural family planning. Women aged 18–40 years were eligible. Daily intercourse records were used to adjust for timing and frequency of intercourse when estimating the per-menstrual-cycle probability of conception. The number of menstrual cycles required to conceive a clinical pregnancy and the probability of sterility and infertility were derived from the estimated fecundability distributions for men and women of different ages.
Sterility was estimated at about 1%; this percent did not change with age. The percentage infertility was estimated at 8% for women aged 19–26 years, 13–14% for women aged 27–34 years and 18% for women aged 35–39 years. Starting in the late 30s, male age was an important factor, with the percentage failing to conceive within 12 cycles increasing from an estimated 18–28% between ages 35 and 40 years. The estimated percentage of infertile couples that would be able to conceive after an additional 12 cycles of trying varied from 43–63% depending on age.
Increased infertility in older couples is attributable primarily to declines in fertility rates rather than to absolute sterility. Many infertile couples will conceive if they try for an additional year.
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