Are newer Ocs any less effective at preventing pregnancy than older ones?

That was the debate waging recently in the media following a 2-day meeting of the US Food and Drug Administration's (FDA's) Advisory Committee for Reproductive Health Drugs. The panel was meeting to discuss possible changes in how the FDA addresses contraceptives, including how clinical trials for these drugs are conducted and how data about the drugs are reported and represented on packaging labels.

But most of the buzz ended up focusing on an agency comment that indicated that the pregnancy rate reported in clinical trials of newer, lower-dose pills has increased from less than 1 to 2 or sometimes slightly more pregnancies per 100 women taking the pills for a year. The agency said the apparent rise might reflect the fact that a greater number of heavier women are now taking the drugs and that clinical trials typically exclude obese women.

Apparently the agency is divided on the need for a cutoff or upper limit for pregnancy rates, and the advisory panel suggested the FDA discard its method for measuring pregnancy rates altogether on the basis that it is outdated.

FDA Statement on Effectiveness of Newer Birth Control Pills, January 23, 2007, and other sources.