What is the positive predictive value (PPV) of a positive fetal fibronectin (FFN) test for preterm labor?

The positive predictive value (PPV) of a positive fetal fibronectin (FFN) test for preterm labor is crucial in clinical decision-making. A significant characteristic of the fetal fibronectin test is its high sensitivity and relatively lower specificity. While the test is proficient in identifying women at risk for preterm labor, the PPV reflects the probability that a positive test result accurately indicates a true case of preterm labor based on the clinical context in which the test is employed.

In practice, the reported PPV of a positive FFN test oscillates with the population's risk of preterm birth. If the baseline risk of preterm delivery in the tested population is not exceedingly high, the PPV can be lower, indicating that not all positive FFN tests necessarily signify the impending onset of preterm labor.

Given that the PPV for a positive FFN test reads around 30% in typical scenarios among women presenting with symptoms such as cervical changes or contractions, it serves as a practical number. That is, while a positive FFN result may suggest risk, it also means that 70% of the women with a positive result may not ultimately experience preterm labor, thus illustrating the limitations of relying solely on this test for clinical decision