Bonnar, J., Flynn, A., Freundl, G., Kirkman, R., Royston, R., & Snowden, R. (1999). Personal hormone monitoring for contraception. The British Journal of Family Planning, 24,128-134.
Key Results
The continuation rate after 13 cycles was 78%. 162 pregnancies occurred in 7209 cycles of use, 67 of which were method-related. The 13-cycle life-table method pregnancy rate was 12.1% (95% confidence interval (CI), 9.3-14.8%). As a result of these findings, the algorithm was changed to increase the median warning of the LH surge from 4 to 6 days. Had this revised algorithm been used, the method pregnancy rate would have been reduced to 6.2% (95% CI, 4.2-8.3%) and method efficacy increased to 93.8%.
Conclusion
The total efficacy rate compares favorably with pregnancy rates in women using other nonhormonal methods of fertility control. Women with cycle lengths of 23-35 days can expect to be required to abstain from intercourse for 6-12 days each cycle.