Length of the Fertile Period

There are 3 objectives to this discussion of the length of the fertile period: 1) review of results from studies of the longevity of sperm and ova within the female reproductive tract; 2) indirect approaches with special attention to Tietzes scheme of analysis; and 3) the application of Tietzes scheme of analysis to 2 additional types of data. Coitus has an appreciable chance of leading to conception only during a relatively short portion of the human menstrual cycle. Despite the practical importance of knowing the length of this fertile period there is no general agreement as to whether it averages closest to 12 24 36 or 48 hours. Studies of the survivorship of sperms and ova within the female all but eliminate the possibility that the fertile period averages as long as 72 hours and case doubt on a mean duration as long as 48 hours. 3 additional estimates have been assembled. The 1st is taken from an analysis by Tietze who estimates the lengths of fertile period that generate reasonable conception delays given in the coital frequencies reported in the female sample of Kinsey et al. The 2nd and 3rd estimates are derived by adapting Tietzes scheme of analysis to data on artificial insemination by donor and to comparisons of conception delays among women reporting different coital frequencies. These 3 lines of evidence provide additional support for the belief that the fertile period typically lasts less than 48 hours. The evidence fails to settle whether the fertile period averages nearly 18 or 36 hours.