The final results of a prospective comparative study of two methods of natural family planning indicate a significant difference in the 12 month net cumulative pregnancy rates between the ovulation and symptothermal methods. These differences are on the order of two to one in favor of the symptothermal method. Pearl pregnancy rates confirm similar differentials between the two methods. Dropout rates for both methods were high. Lack of interest or dissatisfaction with the method was the major reason for dropout training while pregnancy or desire for pregnancy were the major reasons for dropout during the formal phase of the study.
PIP: In a prospective, comparative study in Los Angeles, California (1976-1978), 1247 volunteer couples were randomly assigned to either the ovulation method (OM) or the symptothermal method (STM) of natural family planning (NFP). 12-month Pearl pregnancy rates for both phases of the clinical trial (3-5 month training phase plus formal study phase) showed STM to be more effective (16.6 pregnancies/100 women-years) in preventing pregnancy than OM (34.9 pregnancies/100 women-years). For the formal study phase excluding training, Pearl rates were 13.7 for STM and 39.7 for OM. Both methods showed high dropout rates at 12 months (including training) 74% for OM and 64% for STM. Reasons given during the training phase were lack of interest or method dissatisfaction and during the study phase unplanned pregnancy. Of the 90 pregnancies that occurred during training (59 OM and 31 STM) and 62 during the study phase (42 OM and 20 STM), only 6 OM and none of the STM pregnancies were considered strictly method failures. Other pregnancies were due to inaccurate interpretation of mucus symptoms and failure to follow rules. The unexpected difficulty in recruiting couples is attributed to lack of public awareness of NFP, user satisfaction with and acceptance of other contraception methods, and an unwillingness to adhere to the formal requirements of the study protocol. Two-thirds of the 1247 volunteer couples responded to follow-up 1 year after the study. One-half were still using the NFP method they were taught. The other half had stopped because of desired pregnancy or inconvenience or dislike of the abstinence required.