What is the best biochemical marker to measure for assessing the risk of premature delivery in a pregnant patient?

Fetal fibronectin is a significant biochemical marker used to assess the risk of premature delivery in pregnant patients. This glycoprotein is found at the interface of the fetal membranes and the maternal decidua and can be detected in cervical or vaginal secretions. High levels of fetal fibronectin in these secretions during the second and third trimesters may indicate a higher risk of preterm labor. In particular, if fetal fibronectin is present between 22 and 34 weeks of gestation, it is often used as a predictor for the potential for premature birth within the following week or two.

Inhibin A, alpha-fetoprotein, and human chorionic gonadotropin serve different roles during pregnancy. Inhibin A, for example, is primarily associated with Down syndrome screening and does not provide direct insight into the risk of premature delivery. Alpha-fetoprotein is mainly used to detect neural tube defects and other fetal anomalies. Human chorionic gonadotropin is involved in maintaining early pregnancy and supporting the corpus luteum but does not have predictive capability for preterm labor.

The specific utility of fetal fibronectin as a biomarker for premature delivery makes it the most appropriate choice in this scenario.