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By Mayo Clinic staffFetal fibronectin is a protein that acts as a "glue" during pregnancy, attaching the amniotic sac — the fluid-filled membrane that cushions your baby in the uterus — to the lining of the uterus.
Fetal fibronectin is often present in cervical secretions during early pregnancy. Fetal fibronectin also shows up again later in pregnancy, about one to three weeks before labor begins. If your health care provider is concerned about preterm labor, he or she may test a swab from your cervical canal for the presence of fetal fibronectin. A positive fetal fibronectin test is a clue that the "glue" has been disturbed and you're at increased risk of preterm labor.