Women's sexual experience during the menstrual cycle: identification of the sexual phase by noninvasive measurement of luteinizing hormone

Journal of Sex Research, Feb, 2004 by Susan B. Bullivant, Sarah A. Sellergren, Kathleen Stern, Natasha A. Spencer, Suma Jacob, Julie A. Mennella, Martha K. McClintock

Preovulatory LH Surge in Urine

Participants were required to collect urine samples between 5 and 7 p.m. daily, beginning 1 week prior to the expected day of the preovulatory LH surge and ovulation (Baviera et al., 1988). We calculated the expected day of surge onset based on the regression line for the day of LH surge onset as a function of menstrual cycle length in our laboratory's database of menstrual cycle variables. These urine samples were analyzed by the participants with an enzyme immunoassay (Ovukit[TM], Conception Technology, San Diego, CA) in which the threshold for ovulatory levels of LH was greater than 35 milliInternational Units (mIU).

The noninvasive method for identifying the LH surge and thus pinpointing the day of ovulation we present here differs from traditional methods in two major ways. First, we shifted the sample time from a "first morning sample" collected upon arising to an early evening sample collected between 5 and 7 p.m. before dinner. We did this because the surge detectable in urine typically begins late in the morning or afternoon, after the traditional time for urine collection. We instructed participants to abstain from drinking fluids excessively between 3 p.m. and sample collection to avoid diluting their urine. Second, instead of using the peak of the preovulatory surge as is traditionally done, we used the onset of the surge as the predictor of the day of ovulation and the change in ovarian steroid production. We did this because the interval between the onset of the LH surge and ovulation is significantly less variable than the interval between the peak of the surge and ovulation (reviewed in Stern & McClintock, 1995).

These two changes in timing of sample collection and data interpretation made our method for pinpointing the timing of the LH surge and thereby ovulation significantly more accurate than the traditional method (94% correct vs. 22% correct; p < .001, [chi square] = 35.3, N = 38 cycles, see Figure 1). In a validation study, we created a referent by collecting urine samples six times throughout the day beginning at least 1 day before the preovulatory LH surge until its end. Absolute LH levels in urine were measured with a radioimmunoassay. We selected a subset of the samples, assayed them with a threshold-based enzyme immunoassay, and interpreted the results following the revised protocol described above. We collected another subset and interpreted it following the traditional protocol. A third subset used samples collected at the traditional time, but we interpreted them using the first day of detectable LH rather than the day of its highest level. The accuracy of each protocol was assessed by comparing it to the referent established by the six samples collected each day for several days. In sum, our revised method enables precise identification of the onset of the preovulatory LH surge (onset time within 12 hours with 95% accuracy; Stern & McClintock, 1995). We have used this method successfully for over a decade and have excellent subject compliance (> 95%).

[FIGURE 1 OMITTED]

Estimating the Onset of Preovulatory LH Surge

Vaginal secretions and cervical mucus. Participants recorded in a daily journal three characteristics of their vaginal secretions: consistency, color, and amount. Each of these characteristics had a significant, albeit variable, relationship to the day of ovulation (Stern, 1992). Therefore, we developed an algorithm using all three characteristics that was more accurate than one based on any one characteristic alone. The change in consistency of vaginal secretions was the most accurate for pinpointing the day of ovulation (Stem, 1992). Ovulation occurred most often on the day before the consistency of vaginal secretions changed from wet, slippery, or spinnbarkheit (clear and pliable strands) to tacky, sticky, or dry. If the consistency measure yielded several potential days of ovulation, we used the day that was also indicated by a change in the color characteristic. Ovulation typically occurs on the first day color changes from glassy and/or clear (i.e., estrogenized cervical mucus) to yellow and/or white (i.e. progesterone-influenced and nonestrogenized vaginal cells). Finally, if the consistency and color characteristics did not agree, we used the day indicated by a change in the amount of secretions. Ovulation typically occurs a day before a decrease in amount.