Menstrual fluid loss and its association with body composition, sociodemographic and lifestyle factors, and menstrual health in healthy menstruating New Zealand women : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nutrition and Dietetics at Massey University, Auckland, New Zealand

Abstract

Background: Despite menstruation occurring regularly for most females during their reproductive years, empirical understanding of the volume and variation of menstrual fluid loss (MFL) remains limited. This gap limits our understanding of normal and abnormal menstrual patterns and the biological and sociodemographic factors that may influence MFL. The primary objective of this study was to determine the daily and total MFL over one or up to three consecutive menstrual cycles (MCs). The secondary objectives were to explore the associations between total MFL and sociodemographic and lifestyle factors (including age, ethnicity, and physical activity (PA)), body composition, and menstrual health, including gynaecological age, parity, and hormonal contraceptive (HC) use. Methods: Menstruating females (n=40), aged 18–45 years, were recruited from Auckland, New Zealand, to participate in a prospective observational study collecting MFL. Participants used either a menstrual cup or disc for one or up to three consecutive MCs to measure daily and total MFL. Participants completed a baseline questionnaire that captured sociodemographic data, PA levels, and menstrual and general health history. Anthropometric measurements (height and weight) and body composition (fat mass, fat-free mass, body fat percentage) were collected in a laboratory setting. Descriptive statistics were used to summarise participant characteristics and MFL. Participants were grouped into light-medium and medium heavy groups based on the sample medium. Associations between total MFL and sociodemographic and lifestyle, body composition, and menstrual health factors were explored using independent samples t-tests, Mann-Whitney U, Fisher Freeman-Halton exact tests, Friedman’s ANOVA, and multivariate linear regression. Statistical analyses were conducted using IBM SPSS Statistics (version 30.0) and significance was set at p < 0.05. Results: A statistically significant difference was observed in median MFL across MCs one, two, and three (c2 (1) = 768.0, p < 0.001) and days one to eight (c2 (1) = 167.3, p < 0.001) of menstruation. Significant differences in both objective and subjective MFL were observed between light-medium and medium-heavy MFL groups. Specifically, the medium-heavy group had higher objective MFL, which aligned with a higher subjective rating of MFL on days of menstruation. No significant associations were observed between MFL and sociodemographic and lifestyle (F(4,30) = 0.17, p = 0.95, R2 = 0.03), body composition (F(3,31) = 0.06, p = 0.98, R2 = 0.01) or menstrual health factors (F(3,31) = 0.61, p = 0.61, R2 = 0.06). Conclusion: Menstrual fluid loss exhibited substantial inter- and intra-individual variability. The MFL of this cohort of healthy women appeared to be within the physiologically normal ranges reported in previous literature. No significant associations were found between MFL and sociodemographic and lifestyle, body composition, or menstrual health factors. This highlights the multifactorial nature of menstrual physiology and the need for larger, more diverse studies using objective measurement methods.