在英格兰和威尔士，全部妊娠中约 30% 为非意愿妊娠，所有妊娠中约 20% 流产。[1]Office for National Statistics. Conception statistics: conceptions in England and Wales 2016. March 2018 [internet publication].https://www.ons.gov.uk/peoplepopulationandcommunity/birthsdeathsandmarriages/conceptionandfertilityrates/bulletins/conceptionstatistics/2016[2]National Institute for Health and Care Excellence. Long-acting reversible contraception. September 2014 [internet publication].http://www.nice.org.uk/guidance/cg30 在发达国家中，美国是非意愿妊娠发生率最高的国家之一，全部妊娠中有约一半为非意愿妊娠。其中大约 40% 流产。[3]Hatcher R. Contraceptive technology. 20th ed. New York: Ardent Media; 2011.http://www.contraceptivetechnology.org/the-book/[4]Finer LB, Zolna MR. Declines in unintended pregnancy in the United States, 2008-2011. N Engl J Med. 2016 Mar 3;374(9):843-52.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4861155/http://www.ncbi.nlm.nih.gov/pubmed/26962904?tool=bestpractice.com 美国疾病预防控制中心 (Centers for Disease Control and Prevention) 的报告指出，2008 年至 2014 年期间，年龄为 15 至 44 岁的女性中，流产率已从 19.4‰ 降至 14.6‰，[5]Jones RK, Jerman J. Population group abortion rates and lifetime incidence of abortion: United States, 2008-2014. Am J Public Health. 2017 Dec;107(12):1904-9.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5678377/http://www.ncbi.nlm.nih.gov/pubmed/29048970?tool=bestpractice.com 其中 2014 年的流产数量最低。[6]Jatlaoui TC, Shah J, Mandel MG, et al. Abortion surveillance - United States, 2014. MMWR Surveill Summ. 2017 Nov 24;66(24):1-48.https://www.cdc.gov/mmwr/volumes/66/ss/ss6624a1.htmhttp://www.ncbi.nlm.nih.gov/pubmed/29166366?tool=bestpractice.com 虽然美国的总流产率有所下降，但并非所有人口群体都是如此，弱势群体中非意愿妊娠率和流产率较高。[4]Finer LB, Zolna MR. Declines in unintended pregnancy in the United States, 2008-2011. N Engl J Med. 2016 Mar 3;374(9):843-52.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4861155/http://www.ncbi.nlm.nih.gov/pubmed/26962904?tool=bestpractice.com[5]Jones RK, Jerman J. Population group abortion rates and lifetime incidence of abortion: United States, 2008-2014. Am J Public Health. 2017 Dec;107(12):1904-9.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5678377/http://www.ncbi.nlm.nih.gov/pubmed/29048970?tool=bestpractice.com 这种差异表明，一些女性和青少年的避孕的可及性有限，并指出，有非意愿妊娠风险的所有患者应强调生育控制的重要性。
阅读更多不同地区之间可使用的避孕药有所不同，应查询当地指南。
