Epidemiological studies of natural family planning

Abstract

The prevalence of the use of natural family planning (NFP) can be estimated from sample surveys of married women in the reproductive ages (MWRA). Surveys in developed and developing countries during the past decade indicate that the prevalence of NFP use varies from 0 to 11%. In addition, if one considers NFP use in relation to other contraceptive methods, the percentage of all current contraceptors who use NFP varies from 1 to 35%. This suggests that NFP is an important method in certain countries. Pregnancy rates for NFP vary widely, but most reliable studies report 1-year life-table pregnancy rates between 10 and 25/100 woman-years. The Billings ovulation method consistently has higher pregnancy rates than the sympto-thermal method and NFP users generally have among the highest pregnancy rates compared to other methods. The major safety issue concerning NFP is the risk of adverse pregnancy outcomes associated with aged gametes. There are suggestions from a number of investigations that conceptions distant from ovulation have a higher risk of spontaneous abortion and a higher proportion of male births. The findings with respect to birth defects or multiple pregnancies are less consistent, although some studies have reported an increased risk of chromosomal anomalies.

PIP: This study discusses the epidemiology of natural family planning in terms of prevalence, use-effectiveness, and health risks and benefits. The prevalence of natural family planning among all women of reproductive age is 0-11% in developing countries and 1-13% in developed countries. Prevalence is highest in Catholic countries, such as Peru, the Philippines, Belgium, France, and Poland (11%, 9%, 12%, 7%, and 13% respectively). The number of current contraceptive users using natural family planning ranges from 1-35% in developing countries and 1-23% in developed countries. Life-table pregnancy rates for the Billings ovulation method and the sympto-thermal method vary from 11-26/100 woman-years. The range of user failures is 4-34/100 woman-years as compared with method failures of 0-13/100 woman-years. Pregnancy rates for the calendar rhythm method are higher. Among highly motivated users who want no more children, pregnancy rates are similar to those of diaphragm users and lower than those of users of other intercourse-related methods. The major risks of natural family planning are the risks associated with pregnancy generally, especially in countries with high maternal mortality, and the risks of abnormal pregnancy outcomes due to aged sperm from intercourse prior to the fertile period and aged ova from intercourse after it. Probabilities of conception are highest 1-2 days before estimated time of ovulation. There is an excess of male births conceived during the least fertile days, and the risk of spontaneous abortion doubles outside the period of peak fertility. Furthermore, there is growing but inconclusive evidence linking chromosome abnormalities to aged gametes.