Vitamin D Status Among Infertile Women in Sweden

The goal of this prospective cohort study is to learn about the overall and seasonal prevalence of vitamin D insufficiency and its determinants in a population of women with infertility who will go through in vitro fertilization in Sweden. The main questions it aims to answer are: * What is the prevalence of vitamin D insufficiency? * What are the determinants of this insufficiency? Participants will be asked to complete a questionnaire validated for dietary assessment of vitamin D intake and sun exposure habits and they will leave a blood sample for measurement of 25(OH)D concentration. Researchers will compare the in vitro fertilization outcomes between women with vitamin D insufficiency and sufficiency to see if there is any difference.