NEJM：埋植剂、宫内节育器避孕优于口服避孕药、贴剂和阴道环

《新英格兰医学杂志》(New England Journal of Medicine)5月24日发表的一项前瞻性研究显示，宫内节育器(IUD)和皮下埋植剂预防意外妊娠的作用优于口服避孕药、透皮贴剂和阴道环。使用口服避孕药、透皮贴剂或阴道环者的避孕失败率是使用长效可逆避孕措施者的20倍，原因主要在于口服避孕药、贴剂或阴道环等避孕措施依赖于正确和持续的使用，而IUD和埋植剂一旦置入体内后就可自行发挥作用(N. Engl. J. Med. 2012;366:1998-2007)。

这项前瞻性队列研究由华盛顿大学圣路易斯分校妇产科的Brooke Winner博士及其同事进行，受试者是7,486名因未使用任何避孕措施或仅偶尔避孕而存在意外妊娠风险的女性(14~45岁)。研究者向这些女性告知所有可逆性避孕方法的有效性、风险、益处和副作用，然后让她们自行选择避孕方法并为她们免费提供该方法2~3年。允许受试者在随访期间停止或变更避孕方法，时间不限。研究者每6个月对受试者进行1次电话随访，记录避孕方法使用情况或妊娠状态方面的任何改变，并通过药房处方资料进行证实。

在2007~2011年期间，这些受试者共发生334例次意外妊娠。随访第1年(4.8% vs. 0.3%)、第2年(7.8% vs. 0.6%)和第3年(9.4% vs. 0.9%)，使用口服避孕药、贴剂或阴道环者的意外妊娠发生率均高于使用IUD或埋植剂者。使用长效醋酸甲羟孕酮(DMPA)注射液者的避孕失败率(第1年0.1%，第2年0.7%，第3年0.7%)与使用IUD或埋植剂者相似。从另一个角度来看，使用口服避孕药、贴剂和阴道环者的总避孕失败率为4.55/100人·年，而使用IUD和埋植剂者的总避孕失败率为0.27/100人·年。校正年龄、受教育程度和既往意外妊娠次数后，仍发现使用口服避孕药、贴剂或阴道环者的意外妊娠风险明显高于使用IUD或埋植剂者，危险比(HR)为21.8。

研究者猜测较年轻的女性对避孕措施的依从性低于年龄较大的女性，于是根据年龄来分析数据，结果发现在使用口服避孕药、贴剂或阴道环者中，21岁以下女性的意外妊娠发生率是21岁以上女性的2倍。相比之下，在使用IUD、埋植剂或DMPA注射液者中，21岁以下女性的意外妊娠发生率与21岁以上女性无显著差异。这一结果表明，为青少年提供不需每天、每周或每月依从的长效可逆性避孕措施可能有助于降低该高危年龄组的意外妊娠发生率。

该研究的局限性可能在于，所有避孕方法均免费会提高依从性及导致低估失败率。

该研究获苏珊·汤普森·巴菲特基金会支持。研究者声明与默沙东等多家公司存在联系。


BY MARY ANN MOON
Elsevier Global Medical News
Breaking News

Long-acting contraceptive methods – intrauterine devices and subdermal implants – were superior to oral contraceptives, transdermal patches, and vaginal rings in preventing unintended pregnancies, results from a prospective study of more than 7,000 at-risk women show. The report is in the May 24 issue of the New England Journal of Medicine.

“We found that participants using oral contraceptive pills, a transdermal patch, or a vaginal ring had a risk of contraceptive failure that was 20 times as high as the risk among those using long-acting reversible contraception,” said Dr. Brooke Winner of the department of obstetrics and gynecology, Washington University, St. Louis, and her associates.

The researchers attributed this difference to the fact that once IUDs and implants are inserted, they are not user dependent, whereas the other methods in this study depend on correct and consistent usage by the patient.

Approximately 3 million pregnancies each year in the United States, or half of all pregnancies here, are unintended. This rate is significantly higher than that in other developed countries. Half of these unintended pregnancies are due to incorrect or inconsistent use of contraceptives, and the other half to nonuse of contraceptives.

Dr. Winner and her associates conducted a prospective cohort study of women aged 14-45 years who were at risk for unintended pregnancy because they were not using any contraception or were using it only sporadically. The women received counseling regarding all reversible contraceptive methods, which covered the effectiveness, risks, benefits, and side effects of each (N. Engl. J. Med. 2012;366:1998-2007).

They then were given the contraceptive method of their choice at no cost for 2-3 years. The women were allowed to discontinue or switch methods as often as they wished during follow-up.

The 7,486 study subjects were followed via telephone interviews every 6 months, and any changes in their contraceptive use or pregnancy status were documented in a log. This information was corroborated with pharmacy data where the subjects filled their prescriptions.

Between 2007 and 2011, there were 334 unintended pregnancies in these study subjects.

At 1-year, 2-year, and 3-year follow-up, the women using OCs, patches, or vaginal rings had higher rates of unintended pregnancy than did those using IUDs or implants. The contraceptive failure rates were 4.8% vs. 0.3% at 1 year, 7.8% vs. 0.6% at 2 years, and 9.4% vs. 0.9% at 3 years.

The failure rate for depot medroxyprogesterone acetate (DMPA) injections was similar to that with IUDs and implants: 0.1% at 1 year, 0.7% at 2 years, and 0.7% at 3 years.

Looked at from a different perspective, the failure rate for OCs, patches, and rings combined was 4.55 per 100 woman-years, compared with 0.27 per 100 woman-years with IUDs and implants combined. After the data were adjusted to account for subject age, education level, and number of previous unintended pregnancies, the risk of unintended pregnancy remained markedly higher in women using OCs, patches, or rings than among those using IUDs or implants, with a hazard ratio of 21.8.

The researchers hypothesized that younger women would be less consistent with their use of contraceptives than would older women, so they analyzed the data by subject age to test this hypothesis. They found that subjects younger than 21 years using OCs, patches, or rings were almost twice as likely to have an unintended pregnancy as were older women using those methods.

In contrast, among women using IUDs, implants, or DMPA injections, which do not depend on user consistency, there were no significant differences according to age in the rates of unintended pregnancy.

This finding “underscores the potential benefits of offering adolescents long-acting reversible contraception (which does not require daily, weekly, or monthly compliance) to reduce unintended pregnancies in this high-risk age group,” Dr. Winner and her associates said.

They added that their study was somewhat limited in that all contraception was provided at no cost to the women, “which may have improved adherence and led to an underestimation of failure rates.”

This study was supported by the Susan Thompson Buffet Foundation. Dr. Winner’s associates reported ties to Omnia Education, Merck, Lippincott, and Bayer HealthCare Pharmaceuticals.