This study examines gene expression and gene regulation in the uterine lining during menses in women, for evolutionary comparison with other primates which do or do not menstruate. Samples will be obtained by non-invasive collection of menstrual fluid from healthy donors.

Menstruation corresponds to the shedding of the uterine lining when fecundation has not occurred. This is a recent evolutionary innovation in primates, and the cellular and genetic changes that led to the acquisition of menstruation are not well understood. Additionally, the uterine lining is poorly characterized in humans at the menstrual time point, which hinders both evolutionary and medically-relevant analyses.

In this study, the research team are collecting menstrual fluid samples from healthy female volunteers to profile gene expression and gene regulatory elements in the major cell types that compose the uterine lining during menstruation. The investigators will compare this data to similar samples collected from other primates at the same time point in the female hormonal cycle.

The objective is to identify genes that have acquired novel regulation and/or expression patterns and which may be involved in menstruation.

Inclusion Criteria:

• having regular periods
• being comfortable using silicone menstrual hygiene devices ("cup")
• having giving consent in writing

Exclusion Criteria:

• use of an internal contraception method (hormone or non-hormone based) during or within three months before the study
• pregnancy during or within three months before the study
• amenorrhea (absent periods) during or within three months before the study
• gynaecological intervention or surgery within three months before the study
• hormonal treatment during or within three months before the study
• absence of written consent
• breastfeeding
• medical treatment during the study
• low (< 18.5) or high (> 30) body mass index (BMI)

Healthy female volunteers experiencing regular periods