Ovulation incidence with oral contraceptives: a literature review

Combined oral contraceptives (COCs) provide reliable and convenient contraception, although contraindications and tolerability issues may limit their use in some women. Progestogen-only pills (POPs) may be more suitable for some women, however, traditional POPs do not have the same contraceptive efficacy as COCs. A literature search was performed in order to assess the incidence of ovulation with available COCs, traditional POPs and with a desogestrel POP [Cerazette, 75 microg desogestrel (DSG)]. The following databases were searched: MEDLINE, EMBASE, Biosis, Derwent Drug File, Current Contents and the in-house Organon database 'Docs' (which contains all published reports of Organon products). Searches used free-text terms [e.g. Contraceptive$ in combination with (Ovulat$ adj Rate$), (Ovar$ adj Activ$) or (Escap$ adj Ovulat$)] and were limited to the search criteria 'Human' and 'from 1979 onwards'. The searches included publications up to July 2008.

Many of the studies were hampered by inadequate ovulation criteria; however, the overall incidence of ovulation determined by the reports uncovered in the literature search was 2.0% [95% confidence interval (CI) 1.1-3.3] with COCs containing 30-35 microg ethinylestradiol (EE), 1.1% (95% CI 0.60-2.0) with 15-20 microg EE COCs, 4.6% (95% CI 2.8-6.9) with phasic COCs, 1.25% (95% CI 0.03-6.8) with Cerazette and 42.6% (95% CI 33.4-52.2) with traditional POPs.

The findings indicate that COCs and the desogestrel POP are equally effective in suppressing ovulation, whilst the traditional POP formulations are less effective.