Did contraception reduce teen pregnancy by 86%?

Problems with Explaining Recent Declines... (c) 2007 Ruben Obregon

         The controversy over the contributions of contraception and abstinence on pregnancy rates has grown recently.  A 2007 study published in the Journal of Public Health, which cites data from the 2002 NSFG survey, found that contraceptives are the primary cause of the declining teen pregnancy rates.  Interestingly enough, John Santelli, M.D[1], one of the authors of the study, had previously published an article which found that 53% of the decline in pregnancy rates from 1991 to 2001 was the result of decreased sexual experience among teens. 

In this more recent analysis, he and his co-authors found that decreased sexual activity accounted for only 14% of the reduction in the pregnancy risk index[2] among 15-19 year olds, while improved contraception use is credited with 86% of the reduction.   Among 15-17 year olds, they found that decreased activity accounts for 23% of the reduction in pregnancy risk.  (p. 5)

It is important to distinguish the between the pregnancy rate and pregnancy risk - the 86% reduction applies to the pregnancy risk index only.  Many have misinterpreted these figures to mean 86% of the decline in the pregnancy rate per 1000 adolescent women is due to improved contraceptive use - this is not the case.   In fact, applying this rate of 86% to the overall pregnancy rate overemphasizes the effect of increased contraceptive use and de-emphasizes the decrease in the number of adolescent women who have ever had intercourse.  Unfortunately, one can find this misapplication of the rates on numerous websites on the Internet.

This is much different than the commonly (and mistakenly) cited 86% reduction in pregnancy rates attributed to improved contraceptive use.  Furthermore, the fact that abstinence among previously sexually active teens could account for any reduction in pregnancy risk is encouraging, and shows that there is room for improvement here.

While contraceptive use among adolescents has improved, there are several problems with the study.  To put the study in proper perspective, it essentially analyzes only two groups of teens  - those who had intercourse within the prior 3 months of their participation in the survey, and sexually experienced teens who did not.  [3]  This focus on sexually active and experienced teens, instead of an all teens, is part of a growing trend by some researchers intended  to de-emphasize the contributions of a lack of sexual experience and overemphasize the contributions of contraceptives.

Researchers claim that focusing on the sexually active group results in a more accurate and appropriate analysis since these teens are the ones really at risk of pregnancy.  Yet it seems that these "improved methodologies" are more geared towards arriving at a pre-determined conclusion which shows that contraception, and not the lack of sexual experience, is the answer to reducing teen pregnancy.

Between 1995 and 2002, there was a statistically significant decline of 10% in the number of adolescent women aged 15-19 who were sexually experienced.  Among 15-17 year old women, there was a statistically significant decline of 22%.  

Though the study does mention the decline in sexual experience[4] it makes no real attempt to calculate how much it has contributed to declining pregnancy rates.[5]  Since a lack of sexual experience precludes pregnancy, and a statistically significant increase in those lacking experience occurred from 1995 to 2002, the impact of the lack of sexual experience must be taken into account when analyzing the contributions of abstinence and contraception on pregnancy rates - yet the authors chose not to do so.  

While the authors do not attempt to calculate the contribution of these declines on pregnancy rates, they nevertheless do attribute the decline in pregnancy rates to improved contraceptive use:

 

Overall, increasing rates of contraceptive use appear to be the primary determinant of declining pregnancy rates between 1995 and 2002, and this assessment appears to be consistent with the pattern in other developed countries. (p6) (emphasis added.)

 

Yet, without calculating the contribution of the increase in lack of sexual experience on pregnancy rates, such a conclusion is probably inaccurate and misleading, and simply slants the conclusion in favor of contraceptives.. [6]

The study has other problems as well.  For example, the study overemphasizes the dual use of the pill and withdrawal in calculating the contraceptive risk index, upon which the aforementioned figures of 14% and 86% are based.  It seems that the authors may have assumed that adolescents used multiple methods consistently.[7]  

For example, a teen who relies on the pill and who's partner occasionally uses withdrawal can be said to be using two methods in the same month, but in reality, this is not consistent use of dual methods.  The authors seemingly assumed that such use of both methods was consistent and therefore reflected typical method use - and as a result,  may have derived a much lower failure rate for this combination of methods  than is probably applicable.[8]   

The misunderstood results of this study made headlines across the nation, and the accompanying news stories made it seem as if abstinence only accounted for 14% of the reduction in pregnancy, when in fact it had a much larger impact.  Unfortunately, these misleading figures are still cited in news stories concerning the topic of abstinence and contraception.

This study is cited in other works as proof that increased contraceptive use is the primary reason for the decline in teen pregnancy between 1995 and 2002:   Articles, such as "U.S. Teen Contraceptive Use Up, Pregnancies Down" published in American Journal of Nursing,  [9]and "A flurry of good news", published in Contemporary Sexuality, [10]use this study as evidence of the effectiveness of contraception over abstinence..

The fact that the study essentially ignored the declines in sexual experience is very problematic to say the least, especially since  the proportion of teens that have ever had sex continued to decline during the years of this study.  According to the National Campaign to Prevent Teen Pregnancy (2006), "The proportion of teens who have had sex declined 17% for boys and 9% for girls between 1995 and 2002 (a statistically significant decrease) and among all racial/ethnic groups."       

A recent report provided by the Federal Interagency on Child and Family Statistics shows further evidence of a decline in sexually experienced teens - in 2003, 32.8 percent of 9^th graders had experienced intercourse, down from 36.9 in 1995.   For 10^th graders, 44.1 percent of had engaged in sexual intercourse in 2003, down from 48.0 in 1995.[11]  (Federal Interagency Forum on Child and Family Statistics, 2007, p. 147, Table BEH4.A)

 

Furthermore, the contributions of abstinence and contraceptives vary depending on the time period and data studied.  Kirby (2007) summarizes the aforementioned studies as follows:

 

The overall decline in teen pregnancy in the 1990s reflects both a decrease in sexual activity among teens and an improvement in contraceptive use among sexually experienced teens. However, estimates of the relative contribution of greater abstinence and better contraceptive use vary with the time periods studied, the data sources examined, and the statistical methods used. Careful analyses generally suggest that about 15 percent to 50 percent of the decrease is due to fewer girls having sex, and 50 percent to 85 percent is due to better contraceptive use  (p. 30)

 

Ignoring the contribution in the decline of sexually experienced teens on the overall teen pregnancy rates seems nothing more than an attempt to overemphasize improved contraceptive use at the expense of the decline in sexual experience.  Simply put, it appears that this study paints an incomplete picture of why adolescent pregnancy rates have declined.

(c) 2007 by Ruben Obregon

 

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[1] Credentials:  John Santelli is the Department Chair of the  Population and Family Health department at Columbia University

[2] Santeli et all define the pregnancy risk index as "thus, overall pregnancy risk can be defined as follows: percentage of women who were sexually active multiplied by contraceptive risk index." (p.2)

[3] While Santelli et al  included those who have never had intercourse in calculating their pregnancy risk index, they did not include the reduction in pregnancy due to increased abstinence in their conclusion as to what was the primary determinant of declining pregnancy rates.

[4] Sexual experience is defined as those having experienced sexual intercourse.

[5] The study does partially account for them in determining the means and variance of the pregnancy risk index.  Also, while the study does take into account sexual abstinence among the sexually experienced, in the face of the decline in numbers of sexually experienced adolescents, the total impact of abstinence on teen pregnancy cannot be accurately measured by only considering it among those who are sexually experienced,  yet this study attempts to do so.   At best, the figures cited in this study should only be applied to reduction among the sexually experienced and not all teens.

[6] In order to demonstrate the contribution of the increase in lack of sexual experience and the contribution of increased contraceptive use on overall pregnancy rates, a more thorough methodology that includes two separate calculations would have had to be used, such as the following example:

         

1.             The first calculation would measure how much of the decline in the pregnancy rate was attributable to the increase in the lack of sexual experience, and how much was attributable to declines among sexually experienced teens.    The figure attributed to overall abstinence would indicate what percentage of the decline is related to increased lack of a sexual history.

2.             The second calculation would analyze the decline among those with a sexual history, and would result in two figures - one which would represent the percentage of decrease due to decreased sexual activity, and the other due to improved contraceptive

[7] The NSFG Questionnaire, which was used to collect the data used in the study, does ask women if they used multiple methods in a calendar month and if so, were they were used at the same time.  However, the questionnaire does not ask if they were used together consistently during the month (aside from condom use).  Questions regarding consistent condom use were asked for the past 4 weeks and 12 months (p.87)

[8] The failure rate of the Pill and withdrawal, if consistently used together in a manner that reflects typical use of both methods, is 1.8, and is derived by multiplying the typical failure rate of the pill (7.5) and withdrawal (24.5 ) (.075 x .245 = .018) .  However, this assumes that withdrawal is practiced with the same consistency that someone who uses it as a primary method would - then the typical failure rate of withdrawal could be used.  However, the data does not indicate that withdrawal, when combined with the pill, was used as consistently as one who uses it as a primary method.  The authors seemingly assume both methods were used in a manner that reflects typical use, and therefore, derived a much lower failure rate than may actually be applicable.

[9] Potera, C. (2007), U.S. Teen Contraceptive Use Up, Pregnancies Down.,Journal of Nursing;, 107: 3, p19-19

[10] Melby, T, (2007). A flurry of good news, Contemporary Sexuality; Feb2007, 41:2, p. 1-5

[11] The data for 11^th and 12^th graders, while following a similar trend, was intentionally left out since it did not distinguish between married and unmarried students, and there is a greater and increasing likelihood of a small but significant number of married 11^th and 12^th graders.