Continuous or extended-cycle combined pills prevent pregnancy as well as 21/7 regimens

Design

Systematic review and meta-analysis, 18 RCTs plus 10 other studies

Population

Women using combined oral contraceptives, continuous or extended vs 21/7 or 24/4

Primary outcome

Unintended pregnancy over 1 year

Effect

OR 0.79 (95% CI 0.41 to 1.52); Pearl Index MD -0.20 (-1.31 to 0.92)

This systematic review, prepared for WHO contraceptive guidance, pooled 18 randomised trials and 10 studies of other designs comparing continuous or extended-cycle combined oral contraceptives with conventional 21/7 or 24/4 cycles. Unintended pregnancy over a year did not differ (OR 0.79, 95% CI 0.41 to 1.52), nor did the Pearl Index (mean difference -0.20, -1.31 to 0.92).

Bleeding was the trade: some trials showed fewer total bleeding or spotting days with continuous use, but unscheduled bleeding was more common. The pooled odds of at least one adverse event were modestly higher (OR 1.20, 1.03 to 1.41) — the authors describe this as no significant difference, but the interval as reported sits above 1. The VTE estimate was very imprecise (OR 1.05, 0.16 to 6.79), with the authors estimating about 0.7 extra cases per 1000 users.

In clinic, this supports offering tailored or continuous regimens as a first-line choice rather than a special-case variation — for dysmenorrhoea, menstrual migraine, heavy bleeding, or simply preference. Warn about unscheduled bleeding in the first months, which is the commonest reason women stop. Discontinuation and missing data were higher in the extended arms, which weakens the acceptability findings.

• Offer continuous or extended-cycle pill-taking as a standard option, not only for endometriosis or migraine
• Warn that unscheduled spotting is common early and usually settles; it does not mean the pill has failed
• Apply the same UKMEC or WHO MEC eligibility checks as for cyclic use — VTE risk is driven by the woman, not the regimen
• Ask about the reason for any wish to stop; bleeding pattern is the commonest and often manageable
• Record the chosen regimen clearly so refills match it

Why it matters

The monthly hormone-free week is a convention, not a requirement for safety or efficacy.

Don't overread it

The VTE interval runs from 0.16 to 6.79 — the data cannot exclude a meaningful difference either way.

The statistics, in plain English

An odds ratio of 0.79 with an interval from 0.41 to 1.52 means the data fit anything from about 60% fewer to 50% more pregnancies — so no difference was shown, not proven. The VTE interval is even wider, which is why the absolute estimate of 0.7 extra cases per 1000 users is a rough figure rather than a firm one.

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