Differential fecundity and effectiveness of contraception.

Some years ago my good friend, Alan F. Guttmacher, and his associate, Samuel Rubin, collected from their private practice in Baltimore a series of 1727 pregnancies which occurred after birth control had been discontinued with the purpose of achieving conception. It was my privilege to make a statistical analysis of this material. In our report1 published in 1950, we stated “that the chance of conception was greatest immediately after the discontinuance of contraceptive measures… After the first month the chance of conception declined steadily and rather rapidly… The explanation… is… that couples differ considerably in their ability to achieve pregnancy. Those who conceive most easily do so during the first few months after birth control has been given up. As time progresses, the relatively fecund couples have eliminated themselves and only the less fecund and sterile remain.” It was further pointed out that “a group of couples practicing contraception successfully is not subjected to the selective process by which the more fecund couples are eliminated… Such a population, therefore, retains its high fecundity…“