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Pregnancy Probabilities During Use of the Creighton Model Fertility Care System
Margaret P. Howard, CNFPE;
Joseph B. Stanford, MD, MSPH
Arch Fam Med. 1999;8:391-402.
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.
From Fertility Care Services, Covenant Health System, Lubbock, Tex (Ms Howard); and the Department of Family and Preventive Medicine, University of Utah, Salt Lake City (Dr Stanford). Ms Howard was formerly with the Department of Natural Family Planning, St Joseph's Hospital, Houston, Tex.
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