Ovulation frequency in women of childbearing age attending a population based health survey : the relationship between self-reported cycles and measured serum progesterone levels in The North-Trøndelag health study, The HUNT3-Survey 2006-2008

Abstract

The primary objective was to study the frequency of ovulatory menstrual cycles among women aged 20-50 years participating in the HUNT3-survey. Further, we wanted to investigate how the women’s report of menstrual cycle day coincided with the increase in measured serum progesterone level. Finally, we also investigated the association between self-reported premenstrual symptoms and verified ovulatory cycle, in women who participated in an interview sub-study focusing on the prevalence of premenstrual symptoms. We have used a cross-sectional study design and analysed data from 2063 women reporting no current use of hormonal contraception. The menstrual cycle day was calculated based on the reported first day of the last menstruation. Serum progesterone concentrations were determined by chemiluminescence immunoassay. The cut-off progesterone level for ovulation was set at 8 nmol/L, and the women with progesterone level ≥8 nmol/L were defined as in the luteal phase. The proportion of women with or without progesterone level ≥8 nmol/L from menstrual cycle day 14 until day 20 was assessed, and women with the expected increased level were defined as in a “true” (ovulatory) phase. The association between the measured progesterone level and self-reported premenstrual symptoms was analysed by logistic regression. The median progesterone level reached ≥8 nmol/L at day 15, and 64% of the women were measured at this level at their cycle day 15. The proportion of women in ovulatory phase continued to increase until day 17 where 66% of the women had reached the expected level. From this follows a rather high prevalence of anovulation. No statistically significant differences were found between women in assumed ovulatory and anovulatory cycles concerning anthropometric data, lifestyle or relevant health conditions. Premenstrual symptoms as sore and tender breast (breast symptoms) were the only symptoms associated with being in “true” luteal phase. The results should be regarded with caution: The reliability of the self-report of the first day of the last menstruation is unknown. The mean age of the women was rather high (40.5 years), and the frequency of anovulatory cycles is increasing with age. Also, the influence of storage at -80C over two-four years on the serum progesterone level represents a concern. The study also showed that premenstrual symptoms are relatively prevalent, but only premenstrual breast symptoms are related to ovulation on a statistically significant level.