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

Women's sexuality is not limited to a specific period of estrus, as it is in almost all other mammals. Yet, ovarian hormones clearly modulate women's sexual behavior and even their subjective feelings of sexual desire and attractiveness. Previous research on variation in women's sexuality and emotional well being during the menstrual cycle has returned contradictory results. Many studies have identified a midcycle or periovulatory peak in sexuality (Adams, Gold, & Butt, 1978; Matteo & Rissman, 1984; Stanislaw & Rice, 1988; Udry & Morris, 1968), while other researchers report peaks right before or after menstruation (Bancroft, 1987) and still others report finding no identifiable peak (Meuwissen & Over, 1992). This lack of consensus is likely due to differences in methodology, including the methods for identifying and defining menstrual cycle phase, the aspects of sexuality measured, and the social and reproductive characteristics of the women studied.

Both the evolutionary advantage of coordinating sexual activity with fertility and the majority of existing literature point toward a midcycle increase in sexuality during the ovulatory phase. But, when measures of periovulatory hormones are coarse with error rates that create variation potentially greater than the phenomenon, an unequivocal pattern will be hard to detect. Moreover, the use of different methods to define and identify the hormonal phases of the ovarian cycle precludes direct comparisons across studies.

Menses and ovulation demarcate the hormonally distinct follicular and luteal phases. The most common method for estimating ovulation uses menses onset as the reference point. Participants are asked to make either retrospective reports (e.g., Bancroft, 1987; Warner & Bancroft, 1988) or prospective reports (e.g., Adams et al., 1978) relative to menses. Ovulation is estimated by counting backward 14 days from menses onset, based on the assumption that the luteal phase is relatively fixed in length (Udry & Morris, 1968). In fact, a functional luteal phase following an ovulatory luteinizing hormone (LH) surge varies from 4 to 19 days, introducing a 15-day error (Stern & McClintock, 1998). Counting forward from menses and assuming a 28-day menstrual cycle is even more imprecise, as the normal cycle in fact ranges from 24 to 35 days and the follicular phase varies from 3 to 19 days (Stern & McClintock, 1998).

Other common methods estimate the date of ovulation by measuring midcycle events such as a rise in basal body temperature (Stanislaw & Rice, 1988) or changes in cervical mucus characteristics, which indicate a shift from an estrogen to a progesterone predominant profile (reviewed in Stern & McClintock, 1995). The presence or absence of premenstrual syndrome (PMS) complaints have also been used as indirect indicators of hormonal profiles that may affect sexual behavior (Van Goozen, Wiegant, Endert, Helmond, & Vande Poll, 1997). The best measures are of plasma (Schreiner-Engel, Schiavi, Smith, & White, 1981; Van Goozen et al., 1997) or urinary (Hedricks, Piccinino, Udry, & Chimbira, 1987) hormone levels, but even these have yielded only rough estimates due to the timing of sample collection or interpretation of the data (reviewed in Stern & McClintock, 1995).

In the studies presented here, we changed the timing of a single urine sample collection to take into account the circadian and seasonal rhythms of the preovulatory LH surge. Traditionally, LH is measured in a urine sample collected in the early morning, upon rising. However, in most women the LH surge in urine begins after this and is not detectable until mid-morning. The LH surge measured by plasma usually begins in the early morning and reaches its peak in the evening (Baird, 1983; Baukloh, Fischer, Naether, & Bohnet, 1990; Baviera, Rigano, & Sfameni, 1988; Testart & Frydman, 1982; reviewed in Stern & McClintock, 1995). Moreover, there is a seasonal shift to the circadian pattern so that in the spring many women have LH surges that begin later in the day, around noon (Casper et al., 1988; Edwards, Steptoe, Fowler, & Baillie, 1980; Testart, Frydman, & Roger, 1982; reviewed in Stern & McClintock, 1995). Therefore, we hypothesized that the traditional early-morning collection time increases the risk of being a day or two late in detecting the LH surge, if not missing it altogether.

The traditional approach uses the peak of the LH surge as the predictor of the time of ovulation. However, it is the onset of the surge that is tightly coupled to ovulation, within 30 [+ or -] 2 hours of detection in urine, because the LH surge can have widely different shapes and durations and has been reported to peak from 2 days before ovulation to 4 days after ovulation (e.g., Baird, 1983; Baviera et al., 1988; extensive literature reviewed by Stern & McClintock, 1995). Thus, we tested the efficacy of using the first sample with detectable LH, rather than the sample with the highest level, to pinpoint timing of preovulatory LH surge and the day of ovulation. Our revised method was 95% accurate for detecting the onset within 12 hours as validated by six LH measures per day (see methods below and Stern & McClintock, 1995, for extended rationale and validation).