Background: The need for fitting a contraceptive diaphragm has recently been questioned in the context of upcoming trials in which the ability of the diaphragm to prevent sexually transmitted infections will be tested. Being able to provide the same size device to all women would greatly simplify supplying the device and training the clinicians, provided that it does not compromise effectiveness.
Methods: Data from studies of Lea's Shield and FemCap, in which all women were sized for a standard diaphragm and half were randomized to use it during the studies, were reanalyzed to determine if it was feasible to give all women in a barrier study the same size diaphragm or, alternatively, to determine if diaphragm size could be predicted using an algorithm of one or more parameters.
Results: If all women received a size 70 diaphragm, rather than being fitted by a clinician, 33.2% would receive the same size that they would have received if they had been fitted by a clinician. If the definition of a "correct" fit were broadened to include one size larger or smaller than what the clinician would have prescribed, 78.0% would be "correctly" fitted. Using an algorithm that considered parity, body weight and other factors did not improve results.
Conclusion: It would be acceptable to conduct a trial in which all women receive a size 70 diaphragm, provided that all women are sized; that safety, effectiveness and acceptability are closely monitored and that study results are stratified by the diaphragm size determined by clinician fitting. It would also be informative to use sized diaphragms as the comparator in studies of new single-size devices.