コンドームなどの避妊法に頼っていて妊娠する確率はどれくらい？

以下の各数値は各出典が報告した内容であり、引用した原文の抜粋と算出方法を記載しています。リンクをクリックして直接確認できます。

1. [1] Perspectives on Sexual and Reproductive Health / Sundaram, Vaughan, Kost, Bankole, Finer, Singh & Trussell (Guttmacher Institute) — Contraceptive Failure in the United States: Estimates from the 2006-2010 National Survey of Family Growth 査読済み

   Contraceptive Failure in the United States: Estimates from the 2006-2010 National Survey of Family Growth

   統計値

   First-12-month typical-use failure: male condom 13%, withdrawal 20%, IUD and implant 1%; condom failure down from 18% in 1995. Condom failure 7% at incomes at least 200% of poverty vs 15% at 100-199% of poverty.

   抜粋

   “[Abstract sentences below checked verbatim against the Europe PMC abstract, 2026-09-26] "Long-acting reversible contraceptives (the IUD and the implant) had the lowest failure rates of all methods (1%), while condoms and withdrawal carried the highest probabilities of failure (13% and 20%, respectively). However, the failure rate for the condom had declined significantly since 1995 (from 18%), as had the failure rate for all hormonal methods combined (from 8% to 6%)." [Paraphrase from abstract, not verbatim: the analysis used 15,728 contraceptive use intervals contributed by 6,683 women; women with incomes at least 200% of the poverty threshold had lower condom failure than those at 100-199% of poverty (7% vs. 15%).] ”

   出典データ

   2017-02-28

   アクセス日

   2026-09-26

   計算過程

   Headline native = 13/100 couples pregnant within 12 months of typical male-condom use. Normalized = 0.13 (activity-specific, no further transformation). log10(0.13) = -0.886. Multipliers relative to the 13% condom baseline: IUD/implant 1/13 = 0.08; condom users with income at least 200% of poverty 7/13 = 0.54 (against the all-user average, not against the 100-199% group, whose 15% is 1.15x). The pill's 7% is taken from the Guttmacher fact sheet: 7/13 = 0.54. The 1995 figure of 18% sets the upper end of the uncertainty band. Withdrawal's 20% is cited in prose only (20/13 = 1.54, below the 2x factor bar).

   独立性

   Primary NSFG analysis. The Guttmacher fact sheet below summarizes the same Guttmacher-led estimates and is not independent for the 13% figure; Trussell 2011 (a different data basis and editorial synthesis) and the Walsh 2004 clinical trials are the independent cross-checks.

2. [2] Guttmacher Institute — Contraceptive Effectiveness in the United States 信頼できる参考文献

   Contraceptive Effectiveness in the United States

   統計値

   Male condom: typical-use failure 13%, perfect-use failure 2%. Pill: typical-use 7%. Implant and IUD: under 1% for both typical and perfect use.

   抜粋

   “[Sentences below checked verbatim against the fact sheet, 2026-09-26] "Contraceptive failure rates are defined as the proportion of women who will become pregnant within the first 12 months after initiating method use." "The male condom has a typical-use failure rate of 13%, and a perfect-use failure rate of 2%." "The pill, ring and patch have typical-use failure rates of 7%, and perfect-use failure rates of less than 1%." [Paraphrase, not verbatim: the implant and the IUD are described as the most effective reversible methods, with failure rates under 1% for both typical and perfect use.] ”

   出典データ

   2020-04-01

   アクセス日

   2026-09-26

   計算過程

   Supplies the perfect-use condom figure (2%) that the NSFG cannot measure. Perfect-use multiplier = 2/13 = 0.15. The typical-use 13% matches Sundaram 2017. source_date is the fact sheet's stated month (April 2020); the day is set to the 1st.

   独立性

   Guttmacher summary drawing on Sundaram 2017 (typical use) and Contraceptive Technology (perfect use); not independent of source 1 for typical-use figures.

3. [3] Contraception 83(5):397-404 / Trussell J — Contraceptive failure in the United States 査読済み

   Contraceptive failure in the United States

   統計値

   Percentage experiencing an unintended pregnancy in the first year: male condom 18% typical use, 2% perfect use; no method 85%

   抜粋

   “[Abstract sentences confirmed verbatim via search-engine indexing; journal host unreachable] "This review provides an update of previous estimates of first-year probabilities of contraceptive failure for all methods of contraception available in the United States. Estimates are provided of probabilities of failure during typical use (which includes both incorrect and inconsistent use) and during perfect use (correct and consistent use)." [Paraphrase of the summary table, not verbatim: no method 85%; male condom 18% typical use, 2% perfect use.] ”

   出典データ

   2011-05-01

   アクセス日

   2026-09-26

   計算過程

   18% typical-use condom value sets the upper end of the uncertainty band (0.18). No-method 85% gives the no-contraception contrast: 85/13 = 6.5x the condom baseline. Trussell's table was built partly from older NSFG cycles corrected for abortion underreporting, which is why it runs higher than Sundaram's 13%.

   独立性

   Editorial synthesis in Contraception; Trussell is also a co-author of Sundaram 2017, so the two share methodology lineage, but the 2011 table rests on earlier data.

4. [4] Contraception / Walsh, Frezieres et al. — Effectiveness of the male latex condom: combined results for three popular condom brands used as controls in randomized clinical trials 一次研究

   Effectiveness of the male latex condom: combined results for three popular condom brands used as controls in randomized clinical trials

   統計値

   Clinical breakage 0.4% and slippage 1.1% over the first five condom uses; six-cycle typical-use pregnancy rate 7.0% (95% CI 5.0-9.0), consistent-use 1.0% (95% CI 0.0-2.1); ~800 couples, 3,526 cycles

   抜粋

   “[Abstract sentences confirmed verbatim via search-engine indexing; PubMed and the journal host unreachable] "The combined clinical breakage rate for the first five condom uses was 0.4% for the three latex brands and the combined clinical slippage rate was 1.1%. The combined six-cycle typical-use pregnancy rate for the latex condoms was 7.0% (95% confidence interval 5.0-9.0)." "The combined six-cycle consistent-use pregnancy rate was 1.0% (95% confidence interval 0.0-2.1)." [Paraphrase, not verbatim: data covered 3,526 menstrual cycles from approximately 800 couples using Ramses Sensitol, LifeStyles or Trojan-Enz condoms.] ”

   出典データ

   2004-11-01

   アクセス日

   2026-09-26

   計算過程

   Per-condom breakage 0.4% (about 1 in 250) and slippage 1.1% (about 1 in 90) under trial conditions. Six-cycle typical-use 7.0% in a motivated trial cohort covers a shorter window than the 12-month headline and is not used in the uncertainty band; it is not annualized here because trial dropout and selection make a straight extrapolation unreliable.

   独立性

   Randomized-trial data, independent of the NSFG survey estimates in sources 1-3.

5. [5] Contraception / Steiner et al. (1994) — Breakage and slippage of condoms in family planning clients 一次研究

   Breakage and slippage of condoms in family planning clients

   統計値

   One or more major problems (breakage, slippage, leakage) in 410 of events (10.9%) involving 217 clients (40.2%); breakage in 209 events (5.6%), slippage in 243 (6.5%)

   抜粋

   “[Abstract sentence confirmed verbatim via search-engine indexing; PubMed and the journal host unreachable] "One or more major problems, breakage, slippage, leakage or a combination of these, occurred in 410 (10.9%) events, involving 217 (40.2%) clients." [Paraphrase, not verbatim: data came from 540 clients on 3,754 occasions of condom use over one month; breakage occurred in 209 (5.6%) events and slippage in 243 (6.5%).] ”

   出典データ

   1994-07-01

   アクセス日

   2026-09-26

   計算過程

   Field-use contrast to Walsh 2004: breakage per event 5.6% vs 0.4% in a controlled trial, a roughly 14-fold spread (5.6 / 0.4 = 14). Used in prose and caveats only; not an input to the headline.

   独立性

   Independent 1990s field study in family-planning clients; different population, era and condom stock from Walsh 2004. source_date month approximate.

6. [6] Contraception and Reproductive Medicine / Kakaiya, Lopez & Nelson — Women's perceptions of contraceptive efficacy and safety 査読済み

   Women's perceptions of contraceptive efficacy and safety

   統計値

   Of 500 women aged 18-45, 2.2% correctly estimated typical-use efficacy of both combined oral contraceptives and male condoms; over two-thirds significantly overestimated each

   抜粋

   “[Abstract sentences confirmed verbatim via search-engine indexing; host unreachable] "A convenience sample of 500 women aged 18-45 years, with education levels that ranged from middle school to postdoctoral level was interviewed." "The efficacy in typical use of both combined oral contraceptives and male condoms was correctly estimated by 2.2%; over two-thirds of women significantly overestimated the efficacy of each of those methods in typical use." "The majority of reproductive aged women surveyed substantially overestimated the efficacy of the two most popular contraceptive methods, often saying that they were 99% effective." ”

   出典データ

   2017-06-01

   アクセス日

   2026-09-26

   計算過程

   Perception input only. "99% effective" implies a perceived annual failure of about 1% against a measured 13%, a gap of roughly 13-fold for typical use. Not an input to the headline number.

   独立性

   Independent perception survey; unrelated to the NSFG and trial data.

7. [7] Studies in Family Planning 50(1) / Bradley, Polis, Bankole & Croft — Global Contraceptive Failure Rates: Who Is Most at Risk? 査読済み

   Global Contraceptive Failure Rates: Who Is Most at Risk?

   統計値

   Cites the Sundaram et al. 2017 NSFG 2006-2010 first-year condom failure estimate as 12.6 (SE 1.11), against a pooled 43-country DHS condom estimate of 8.6

   抜粋

   “[Paraphrase from search-engine indexing of the article, not verbatim; PMC and the publisher host unreachable from the authoring environment] In comparing its pooled Demographic and Health Survey estimates with US figures, the article reports the Sundaram et al. (2017) condom failure estimate from 2006-2010 NSFG data as 12.6 with a standard error of 1.11, lower than earlier US rates but higher than its own global condom estimate of 8.6. ”

   出典データ

   2019-02-01

   アクセス日

   2026-09-26

   計算過程

   95% interval = 12.6 +/- 1.96 x 1.11 = 12.6 +/- 2.18 = 10.4% to 14.8%. The lower limit, rounded down to 0.10, sets the low end of the uncertainty band. The standard error should be confirmed against Sundaram 2017's own table on verification.

   独立性

   Secondary report of the Sundaram 2017 standard error; not independent of source 1 for the condom figure. Its own DHS estimates are not used here.

8. [8] Centers for Disease Control and Prevention — Unintended Pregnancy | Reproductive Health | CDC ↗ 1 other entry 政府報告書

   Unintended Pregnancy | Reproductive Health | CDC

   See all 2 Likelier entries citing this source →

   統計値

   41.6% of US pregnancies in 2019 were unintended; rate 35.7 per 1,000 females aged 15-44

   抜粋

   “"The percentage of U.S. pregnancies that were unintended declined from 43.3% in 2010 to 41.6% in 2019. Unintended pregnancy rates declined by 15%, from 42.1 per 1,000 females aged 15-44 years in 2010 to 35.7 per 1,000 in 2019. Despite this progress, about 4 in 10 pregnancies in the United States are still unintended." ”

   出典データ

   2024-01-01

   アクセス日

   2026-05-10

   計算過程

   Context only, not an input to the headline. Excerpt reused from the verified citation in the getting-tubal-ligation regret-pair (accessed 2026-05-10); cdc.gov was not reachable from this session. Unintended pregnancies include those with no method in use, so this share cannot be attributed to contraceptive failure alone.

   独立性

   National surveillance-based estimate, independent of the method-specific failure data.