Study designs of evaluations included in the review
All available data from human clinical and pharmacokinetic trials performed in Europe, Canada and the US were included; both comparative and noncomparative studies were included because of the paucity of direct comparative information available. Eight of the 17 included studies were randomised.
Specific interventions included in the review
The newer progestins desogestrel, norgestimate and gestodene are compared with each other and to older oral contraceptives levonorgestrel, norethisterone, norgestrel and norethindrone.
Participants included in the review
Women taking oral contraceptives were included.
Outcomes assessed in the review
Efficacy was measured using either the pearl index (number of pregnancies per 100 women-years of use), life table data the number of women in 100 who would become pregnant during the cumulative cycle exposure, the percentage of pregnancies occurring over 6 cycles, or cumulative 6-cycle life table pregnancy rate.
Cycle control was assessed using the following measures: breakthrough bleeding, spotting, dysmenorrhea, amenorrhea and length of bleeding. Definitions of breakthrough bleeding and spotting varied between studies, as well as between times when these parameters were recorded. Adverse effects were also reported under the following headings: androgenicity, acne, hirsutism, weight gain, blood-pressure and haemostasis.
How were decisions on the relevance of primary studies made?
The author does not state how the papers were selected for the review, or how many of the reviewers performed the selection.