The Cochrane Fertility Regulation Group: synthesizing the best evidence about family planning.

The Fertility Regulation Group of the Cochrane Collaboration has been assessing the best available evidence on fertility regulation, family size and birth spacing. By the end of 2005, this group had published 32 systematic reviews and 12 protocols; most reviews were on contraception. Because of suboptimal trial quality, firm conclusions could be made in only five reviews. Threats to internal validity in published trials include the absence of description of allocation concealment, intentional exclusion of participants after randomization, failure to use intention-to-treat analyses and lack of treatment blinding. The precision of results has been limited by small sample sizes. The finding that most trials of oral contraceptives were conducted by pharmaceutical companies raises concerns about potential commercial bias. Of necessity, most information about fertility regulation effectiveness and adverse effects comes from observational studies, which vary widely in quality. Systematic reviews of evidence, with an emphasis on randomized controlled trials when available, will continue to improve fertility regulation in the years ahead.