Period proteins reshape blood chemistry and relate to reproductive health

Researchers report that about 198 blood proteins change in four distinct patterns across the menstrual cycle, and a 75-protein score can estimate cycle day from a single blood draw, explaining over 40% of variation.

Monthly menstrual cycles reshape the chemical makeup of the bloodstream. Researchers report that about 198 proteins in blood follow four distinct patterns across the cycle. These proteins include signals tied to immune function, tissue repair and blood vessel activity. The findings link many cycling proteins to conditions such as endometriosis, fibroids and heavy or irregular bleeding. Key findings: - 198 blood proteins were observed to follow four distinct pattern groups across the menstrual cycle, with some rising during menstruation and others peaking at ovulation or after ovulation. - A score based on 75 protein measurements estimated cycle day from a standard blood sample and captured over 40% of the variation in cycle timing, while a single estrogen measurement explained almost none. - Several cycling proteins are associated with reproductive conditions; one protein tied to uterine lining growth was linked to more than double the risk of heavy, frequent, or irregular bleeding. - Genetic analyses reported that higher levels of a follicle-stimulating protein, which rises early in the cycle, are associated with increased risk of endometriosis, heavy bleeding and fibroids. Summary: The study reframes the menstrual cycle as a coordinated, body‑wide biochemical rhythm with measurable effects on hundreds of circulating proteins and links to several reproductive conditions. The authors report that protein-based measures may improve the timing interpretation of routine blood tests and support earlier or more accurate detection of reproductive disorders, and further development and validation are reported as needed.