Collection of particulate matter on bedroom window Participants will be asked to clean their bedroom window with clear water on the in- and outside around 24 weeks of gestation. A poster (A4 format) will then be attached to the window to create a standardized area for the measurement of magnetic particles. After minimal 4 weeks, the area in the poster is cleaned with a sterile pre-injection swab, on both sides of the window. Swabs are transported in a plastic bag and the ferro(i)magnetic particulate matter fraction will be quantified by Saturated Isothermal Remanent Magnetization.