Objective: To determine the potential efficacy of two simple fertility awareness-based methods of family planning-the Standard Days Method and the TwoDay Method-among breastfeeding women.
Design: Analysis of pre-existing data set, collected in 1986-1990.
Setting: Pre-existing data from Australia, Britain, and Canada.
Patient(s): Seventy-three breastfeeding women in Australia, Britain, and Canada, who were followed starting 42 days postpartum, until they had at least two potentially fertile cycles (defined as cycles with adequate levels of urinary estrogens (E) and pregnanediol glucuronide and a long enough luteal phase to support a pregnancy). We examine this existing data set.
Main outcome measure(s): Probability of pregnancy from intercourse on different days of the cycle relative to ovulation for breastfeeding women following the instructions of the Standard Days Method or the TwoDay Method.
Result(s): These two methods may be appropriate for different groups of breastfeeding women at different times. The Standard Days Method may be appropriate after cycle regularity is established, whereas the TwoDay Method may be a more effective option earlier in the postpartum period.
Conclusion: A need remains for a more appropriate simple fertility awareness-based method during this early period.