Evolution of Menstruation

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.

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)