Breastfeeding and the symptothermal method.

This prospective study was conducted among experienced users of periodic abstinence methods in Sydney, Montreal, and Birmingham (England) in order to describe the relationship between a laboratory measurement of ovulation and the natural symptoms of fertility during breastfeeding. Daily urinary estrogen and pregnanediol glucuronide assays were used to estimate the date of ovulation and to determine potentially fertile days. A standard set of Symptothermal Method (STM) rules was applied to daily STM records to assess the correspondence of the natural symptoms of fertility to the underlying hormonal profile. The STM symptoms and rules accurately identified 77-94 percent of the women's potentially fertile days, but abstinence was also recommended on about half of the days when the women were not fertile. An integrated set of common rules for STM use during breastfeeding is highly sensitive but not specific in its ability to screen for ovulation.