What is the best biochemical marker to measure to assess the risk of delivering prematurely?

• A. Inhibin A
• B. a1-Fetoprotein
• C. Fetal fibronectin
• D. Human chorionic gonadotropin

Answer: (C)

Fetal fibronectin in cervicovaginal secretions is the best marker for assessing risk of preterm delivery. It is a protein produced at the fetal–maternal interface, and when it appears in vaginal secretions between roughly 22 and 34 weeks, it signals disruption of the fetal membranes or cervical remodeling that can precede premature birth. A negative result has a high negative predictive value, meaning a low likelihood of delivery in the near term, which helps clinicians avoid unnecessary interventions. A positive result indicates higher risk, though it’s not definitive and is interpreted alongside cervical length and clinical symptoms.

The other markers listed — inhibin A and alpha-fetoprotein, and hCG — are used mainly for fetal anomaly screening or dating rather than predicting imminent preterm delivery. They don’t reliably indicate the risk of delivering prematurely.