Sex Research Update
McKay, Alexander, The Canadian Journal of Human Sexuality
This instalment of Sex Research Update summarizes recent research on: why teenage pregnancy rates in the United States are declining; teen perspectives on pregnancy prevention; determinants of low-risk and high-risk HPV infections among Montreal university students; university students' knowledge and awareness of HPV; knowledge and use of emergency postcoital contraception by female students at a high school in Nova Scotia; and an HIV prophylaxis program for sexual assault victims in British Columbia.
Darroch, J.E. & Singh, S. (1999). Why Is Teenage Pregnancy Declining? The Roles of Abstinence, Sexual Activity and Contraceptive Use, Occasional Report. New York: The Alan Guttmacher Institute, No. 1.
Although the United States continues to have one of the highest teenage pregnancy rates in the developed world (nearly double that of Canada), the teen pregnancy rate in the U.S. dropped during the 1990s. The objective of the Darroch and Singh report is to examine the contributions of changes in abstinence, sexual behaviour, and contraceptive use to declines in the teenage pregnancy rate during the 1990s. Their analysis is based on data from the 1988 and 1995 cycles of the National Survey of Family Growth as well as recent data on rates of teenage pregnancies, births, and abortions for their analysis.
Between 1988 and 1995, the pregnancy rate among 15- to 19-year-olds declined from 111 to 101 per 1,000. During this time frame, the proportion of teenagers who had ever had intercourse decreased from 52.6% to 51.3%. During the same time period, the pregnancy rate among sexually experienced young women declined from 212 to 197 per 1,000. According to the authors, the relative contributions of the declining proportion of teenage women who had ever had intercourse and the pregnancy rate among sexually experienced teenage women can be estimated by calculating what the pregnancy rate would have been if only one of these factors had changed.
These calculations indicate that roughly one-fourth of the drop in the teenage pregnancy rate between 1988 and 1995 resulted from increased abstinence (i.e., a decline in the proportion of young women who had had sex), and approximately three-fourths from decreased pregnancy rates among sexually experienced teenagers (p. 9).
The authors then turn their attention to the question of how sexually experienced teenagers have become more successful at preventing pregnancy. They investigate three possible factors: a decrease in the frequency of intercourse; an increase in the use of contraceptives in general; and an increase in the use of more effective contraceptive methods. With respect to the frequency of intercourse, the average number of months in a year that a sexually experienced teenager had had intercourse at least once was 8.6 months for both the 1988 and 1995 samples. The proportion of sexually active youth who reported having intercourse four or more times a week grew from 4% in 1988 to 10% in 1995. For contraceptive use, 75% of sexually experienced youth reported using a contraceptive at first intercourse in 1995 compared to 65% in 1988. However, among sexually active youth, the proportion who had used a method at last intercourse decreased from 85% to 83% between 1988 and 1995. It appears that the decline in the pregnancy rate among sexually experienced youth is attributable, in large degree, to the increased use of long-acting hormonal contraceptive methods such as the injectable and the implant which have very low failure rates. Introduced in the early 1990s, these methods accounted for 13% of adolescent contraceptive use by 1995.
Primarily because of this shift to long-acting methods, overall contraceptive effectiveness among teenagers improved between 1988 and 1995 -- or put another way, teenage contraceptive users grew less likely to become pregnant. Given the method patterns of contraceptive users in 1988, an estimated 16% became pregnant within a year after beginning use; by 1995, the proportion had dropped to 15% - a very modest improvement in absolute terms, but roughly a 9% decline (p. …