A mathematical model study of contraceptive efficiency and unplanned pregnancies

Abstract

How effective are contraceptives in maintaining desired family size? A mathematical model designed to study fertility data (FERMOD) was given information pertinent to the typical American family, including probable age of marriage, number of children desired, fertility, etc. It was found that if 100 such couples rely on a contraceptive 95 per cent effective (such as the diaphragm or condom) after reaching a desired family size of 3 children, over 80 of them would have more children during the remaining 12 to 15 year period of fertile marriage. About 3 to 6 of these couples would end up with 7 children. If a 99 per cent effective method (such as the pill, perhaps the IUCD) was used, about 30 of these couples would end up with more children than planned. In the context of clinical realities of current contraceptive technology and the illegality of abortion as a means of regulating family size, these calculations are very persuasive toward favoring voluntary sterilization at some point after the family is considered complete, at least until better contraceptives come along.