Pregnancy probabilities during use of the Creighton Model Fertility Care System

Objective: To evaluate pregnancy probabilities during use of the Creighton Model Fertility Care System (CrMS). Design: Couples who began use of the CrMS were entered into this observatio nal cohort study. Follow-up included detailed reviews of use of the CrMS. P regnancy probabilities were calculated with both net and gross life-table a nalysis through 18 months. Setting: A natural family planning service delivery program based at an urb an hospital in Houston, Tex. Subjects: A group of 701 couples who received instruction in the CrMS were entered into the study. Most couples (93%) were engaged or married. Most wo men were white (83%), between the ages of 20 and 34 years (88%), and colleg e graduates (58%). Main Outcome Measure: Pregnancies were classified based on a detailed evalu ation involving the pregnant woman (usually with her partner). Results: At 12 months, the following net pregnancy probabilities were found per 100 couples: method-related pregnancies, 0.14; pregnancies caused by u ser and/or teacher error, 2.72; pregnancies caused by achieving-related beh avior (genital contact during a time known to be fertile), 12.84; unresolve d pregnancies, 1.43; and total pregnancies, 17.12. Pregnancy probabilities were similar when stratified by the following reproductive categories: unco mplicated regular cycles, long cycles, discontinuing oral contraceptives, b reastfeeding, and other. Conclusions: Pregnancy probabilities of the CrMS compare favorably with tho se of other methods of family planning. Most pregnancies result from genita l contact during a known fertile time. Women need not have regular cycles t o use the CrMS successfully.