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 observational cohort study. Follow-up included detailed reviews of use of the CrMS. Pregnancy probabilities were calculated with both net and gross life-table analysis through 18 months.
Setting: A natural family planning service delivery program based at an urban 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 women were white (83%), between the ages of 20 and 34 years (88%), and college graduates (58%).
Main outcome measure: Pregnancies were classified based on a detailed evaluation 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 user and/or teacher error, 2.72; pregnancies caused by achieving-related behavior (genital contact during a time known to be fertile), 12.84; unresolved pregnancies, 1.43; and total pregnancies, 17.12. Pregnancy probabilities were similar when stratified by the following reproductive categories: uncomplicated regular cycles, long cycles, discontinuing oral contraceptives, breastfeeding, and other.
Conclusions: Pregnancy probabilities of the CrMS compare favorably with those of other methods of family planning. Most pregnancies result from genital contact during a known fertile time. Women need not have regular cycles to use the CrMS successfully.