Fetal fibronectin is a proteinaceous material produced by fetal cells. This material is also referred to as natural adhesive since its role is to 'glue together' the fetal sac and the uterine lining. Reference: https://www.mayoclinic.org/tests-procedures/fetal-fibronectin/about/pac-20384676#:~:text=Fetal%20fibronectin%20is%20a%20protein,into%20secretions%20near%20your%20cervix. Image via: https://www.news-medical.net/news/20180314/The-Importance-of-Fetal-Fibronectin-Testing-for-Women-with-Symptomatic-Preterm-Labor.aspx