Ball, M. (1976). A prospective field trial of the ovulation method of avoiding conception. European Journal of Obstetrics, Gynecology and Reproductive Biology, 6(2), 63-66.
Key Results
The survey showed an overall unplanned pregnancy rate of 15.5 per 100 women years. Only four pregnancies occurred to couples who confined intercourse to the preovulatory dry days and to the postovulatory days from the fourth day after the peak symptom, giving a biological failure rate of 2.9 pregnancies per 100 women years.
Conclusion
The results of this study may be compared with those achieved in prospective studies of other natural methods of conception control.