Aim: We aimed to evaluate the combined value of placental alpha microglobulin-1 (PAMG-1) and cervical length (CL) via transvaginal ultrasound for assessing risk of imminent spontaneous preterm delivery in patients presenting with threatened preterm labor (PTL). Methods: Clinical exam, PAMG-1 test, cardiotocography, and CL measurement via transvaginal ultrasound were performed on all patients meeting inclusion criteria. Ninety-nine patients at 22⁺⁰–36⁺⁶ gestational weeks with the symptoms of PTL were included. The interval between sample collection and delivery was measured for each method. Results: Performance metrics were calculated for PAMG-1 test, CL < 25 mm, and contractions ≥ 8/h. The sensitivity, specificity, positive predictive value, and negative predictive value for the PAMG-1 test were 100%, 95%, 75%, 100% and 100%, 98%, 88%, 100% for 7 and 14 days, respectively; the respective values for CL < 25 mm were 83%, 59%, 22%, 96% and 79%, 59%, 24%, 94% for 7 and 14 days; and those for contractions ≥ 8/h were 42%, 38%, 8%, 83% and 43%, 38%, 10%, 80% for 7 and 14 days. Specificity for the PAMG-1 test was statistically significant (P < 0.001) in pairwise comparisons for all other methods. Patients were divided into four groups for analysis of PAMG-1 test performance as follows: CL < 15 mm (100%, 100%, 100%, 100% and 100%, 100%, 100%, 100% for 7 and 14 days, respectively); CL < 25 mm (100%, 94%, 83%, 100% and 100%, 97%, 92%, 100% for 7 and 14 days, respectively); CL of 15–30 mm (100%, 95%, 64%, 100% and 100%, 97%, 82%, 100% for 7 and 14 days, respectively); and CL ≥ 30 mm (100%, 100%, 100%, 100% and 100%, 100%, 100%, 100% for 7 and 14 days, respectively). Conclusion: The use of the PAMG-1 test in patients with a CL of 15–30 mm is highly predictive of imminent spontaneous preterm delivery in women presenting with threatened PTL and could save hospital resources.