Variation in couple fecundity and time to pregnancy, an essential concept in human reproduction

• Published in: The Lancet (British edition) Vol. 355; no. 9219; pp. 1928 - 1929
• Main Authors: te Velde, ER, Eijkemans, R, Habbema, HDF
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 03.06.2000; Elsevier Limited
• Subjects: Birth Rate; Fecundity; Female; Fertility; Fertilization; Humans; Infertility; Male; Pregnancy; Reproduction; Time Factors
• ISSN: 0140-6736; 1474-547X
• DOI: 10.1016/S0140-6736(00)02320-5

With a high monthly fertility the average time to pregnancy is short, and vice versa.4 Survival analysis is the appropriate method for assessing time-to-pregnancy data. Since the more-fertile couples tend to conceive first, as time goes by progressively less-fertile couples selectively remain in the population of couples who have not achieved a pregnancy.5 Hence how long couples have been unsuccessful at conceiving is an essential estimate of the degree of subfertility. The figure, which is derived from data collected by Bongaarts in natural, non-contraception-- practising populations1 and based on a sterility rate of 4%, shows that, as the duration of inability to achieve a pregnancy increases, the probability of success during the subsequent year sharply decreases. However, the data also show that, if the unproductive period is short (eg, 12 months), the probability of success is still considerable-half the couples will conceive during the following year. These reasonable pregnancy prospects illustrate that the definition of infertility as a failure to conceive within a year contains an oversimplification that may result in premature resort to assisted-reproduction techniques, with their associated risks.