Frank-Herrmann P, Freundl G, Burr S, et al. Effectiveness and acceptability of the symptothermal method of natural family planning in Germany. Am J Obstet Gynecol 1991; 165: 2052–4.
Key Results
For natural family planning–only users, the Pearl rate for unplanned pregnancy was 2.3 and for mixed-method users 2.1.
Conclusion
Most pregnancies resulted from unprotected intercourse during the fertile phase, and the use of barrier methods does not reduce risk-taking.