This multi-center contraceptive effectiveness and safety study of the SILCS diaphragm will enroll approximately 450 couples at risk for pregnancy at six study sites in the U.S. The study will randomly assign approximately 300 couples to use the SILCS diaphragm with BufferGel and approximately 150 couples to use the SILCS diaphragm with Gynol II (2% N-9 gel). At two sites, a substudy involving colposcopy and microflora will be conducted in about 80 women (40 at each site). The primary objective of this study is to estimate the cumulative 6-month typical-use pregnancy probability for women using the SILCS diaphragm with a contraceptive gel.