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.
PIP: Periodic abstinence from sexual intercourse as a pregnancy prevention technique is sometimes the sole method used by women. The effectiveness of this technique is based on the woman's ability to fully understand her own menstrual cycle. Factors like breastfeeding and endocrine irregularities have been shown to interfere with a women's ability to determine periods of fertility. This article reports on a prospective study on the relationship between breastfeeding and hormonal levels, as a measurement of fertility, in women using periodic abstinence. The 73 women in this study were from England, Canada, and Australia. All women were breastfeeding. Daily symptothermal method (STM) records, which documented the cervical mucus conditions and basal body temperature, were kept. All women had experienced healthy pregnancies. Chi-square analysis and the analysis of variance (ANOVA) were the statistical methods employed. Significantly less abstinence is recommended by the STM rules during the anteovulation stage than during either of the later stages. Significantly less abstinence is also recommended during amenorrhea than after the first menstrual period. During the anteovulation stage, significantly fewer days were reported with fertile-type mucus than later stages. First ovulations were reported in 48 women (65%) during amenorrhea; of these, 25 (52%) were characterized as having adequate luteinization for conception. The STM method used in this study was considered to be sensitive but lacked specificity.