Women's Health Study (WENDY)-a protocol of a population-based study assessing gynecological and metabolic health in women in their mid-30s.

The Women's Health Study (WENDY) was conducted to improve insights into women's health and health burden. It provides a unique, comprehensive data source that can be broadly utilized to understand gynecological symptoms, diseases, and their relation to metabolic and overall health more deeply in a population-based setting. The study was conducted in Finland from May 2020 to October 2022. It included 1918 women (33-37 years old) who were born in northern Finland between July 1985 and December 1987. Data collection comprised one 3- to 4-hour study visit that included clinical measurements, biological samples, ultrasound examinations and an extensive questionnaire on gynecological and reproductive history, physical and mental health, quality of life, lifestyles, current life situations, health awareness, and opinions. The study also included a menstrual cycle follow-up and cognitive testing up to 3 months via a mobile application. Given that all participants' data can be linked to all Finnish national registers, and the Northern Finland Birth Cohort participants' data can be linked to the birth cohort data set collected from gestational week 24 onward, WENDY study forms one of the largest data sets worldwide to investigate gynecological and metabolic health burden in women.