Failure rates with long-acting reversible contraceptive (LARC) methods are lower than those of oral contraceptives, transdermal patches or vaginal rings in women of all ages, a prospective cohort study from the US has concluded.

The Contraceptive CHOICE project recruited women aged 14-45 years from August 2007 to September 2011. The women were a convenience sample, recruited from referrals by medical providers, newspaper reports, study fliers and word of mouth.

A total of 8,445 women enrolled in the study and 7,486 met the eligibility criteria for analysis.

Participants were given information about all reversible contraceptive methods including effectiveness, benefits, risks and side effects. They were provided with their preferred method at no cost. Women were allowed to switch methods during the follow-up period. Participants were incentivised with a $10 gift voucher for every follow-up interview and were followed up at three and six months and then every six months thereafter.

The primary outcome measure was contraceptive failure; pregnancy rate by age group was the secondary outcome.

Women who chose the pill, patch or ring were more likely to be nulliparous, have private health insurance, and less likely to have had a previous unplanned pregnancy, abortion or STIs. Those who chose depot medroxyprogesterone acetate (DMPA) injection were more likely to be black, less educated, lower socioeconomic status, have no health insurance and to have a history of STIs. Those who chose an IUD or implant were more likely to be older, have public health insurance or have higher parity.

There were 334 unintended pregnancies over the study period;156 of these were attributed to IUD, implant, DMPA, pill, patch or vaginal ring failure. Participants using the pill, patch or vaginal ring had higher rates of unintended pregnancy than those using LARC at all yearly time points (see table 1, below).

The contraceptive failure rate for the pill, patch or ring was 4.55 per 100 women-years, 0.22 for DMPA injections and 0.27 for IUDs or implants (P < 0.001).

The risk of unintended pregnancy among users of the pill, patch or ring was higher compared with those using LARC hazard ratio (HR), 21.8 (95% CI: 13.7-34.9), even when adjusted for age, education and number of previous unintended pregnancies.

Younger women (< 21 years) who used the pill, patch or ring had a higher rate of unintended pregnancy compared with older women using the same methods; HR after adjustment for education and history of unintended pregnancy was 1.9 (95% CI: 1.2-2.8). Failure rate did not differ significantly in women of different age groups who used DMPA injections and IUDs or implants.

Some GPs still consider LARC (especially intrauterine methods) as unsuitable for nulliparous and younger women. There is no evidence for this assertion and this study states the contrary. It found that long-lasting methods of contraception are superior in reliability to contraceptive pills, patches and vaginal rings in preventing unintended pregnancies across all age groups. The failure rates are higher in younger women who use the pill, patch or vaginal ring.

Apart from being more reliable, all LARC methods are deemed cost-effective by NICE. We must continue to offer LARC as an option to women who may benefit.

Dr Richard Ma

• Winner B, Peipert JF, Zhao Q et al. Effectiveness of long-acting reversible contraception N Engl J Med 2012;366: 1998-2007