Oral Contraceptive Efficacy and Body Weight: Does Obesity Affect the Risk of Contraceptive Failure?

The blood spot validation portion of the study tests the hypothesis that progesterone assays from self-collected daily blood spots are equivalent to serum samples, and that the values obtained can identify women that ovulate. After validating collection methods, enrollment will begin for the feasibility portion of the study looking at thin and heavy women on birth control pills. All women in this portion of the study will take a very-low dose birth control pill that is normally available through a doctor's office. During each month of the study, women will have their blood pressure and weight recorded, and have their blood drawn twice per week or use a finger stick kit daily at home to check for the natural hormones and brain chemicals that tells if an egg develops. During the last week of each menstrual cycle (period week), women will also have their blood drawn to measure the levels of hormone found in the birth control pill. Women will also need to report in a written diary that they have taken their birth control pill for the day.