Low Levels of Complement Factor H in the First Trimester of Pregnancy Are Associated with Spontaneous Preterm Birth

Preterm birth (PTB) remains a significant public health concern, and prediction is an important objective, particularly in the early stages of pregnancy. Many studies have relied on cervical characteristics in the mid-trimester, with limited results. It is therefore crucial to identify novel biomarkers to enhance the ability to identify women at risk. The complement pathway is implicated in the process of placentation, and recent proteomics studies have highlighted the potential roles of some complement proteins in the pathophysiology of PTB. To determine the association between the occurrence of spontaneous preterm birth (sPTB) and the concentration of complement C3, factor B, and factor H in the blood of pregnant women during the first trimester. This prospective cohort study included women with singleton pregnancies, both with and without a history of sPTB, from two health institutions in Bucaramanga, Colombia. The outcome was sPTB before 37 weeks. A blood sample was obtained between 11 + 0 to 13 + 6 weeks. ELISA immunoassay was performed to quantify the levels of C3, factor B, and factor H. A total of 355 patients were analyzed, with a rate of sPTB of 7.6% (27/355). The median plasma concentration for C3, factor B, and factor H were 488.3 μg/mL, 352.6 μg/mL, and 413.2 μg/mL, respectively. The median concentration of factor H was found to be significantly lower in patients who delivered preterm compared to patients who delivered at term (382 μg/mL vs. 415 μg/mL; p = 0.034). This study identified a significant association between low first-trimester levels of factor H and sPTB before 37 weeks. These results provide relevant information about a new possible early biomarker for sPTB. However, the results must be confirmed in different settings, and the predictive value must be examined.