Placental α-microglobulin-1 in cervicovaginal fluid and cervical length to predict preterm birth by Thai women with symptoms of labor

Background: Presence of placental a microglobulin-1 (PAMG-1) in cervicovaginal fluid is a bedside test to predict preterm delivery. Objective: To determine whether the accuracy of a positive PAMG-1 test result to predict preterm birth within 7 days and 14 days in our hospital setting can be improved by adding cervical length. Methods: We recruited 180 pregnant women who attended the labor ward of Siriraj Hospital, Thailand, from 2016 to 2018 for this prospective observational study of diagnostic accuracy. We used data from 161 women who met inclusion criteria including symptoms of preterm labor between 20(0/7) and 36(6/7) weeks' gestation without ruptured membranes and with cervical dilatation <3 cm and effacement <80%. Presence of PAMG-1 in cervicovaginal fluid was tested using a PartoSure kit, cervical length was measured by transvaginal ultrasound, and the time to spontaneous delivery was calculated. Results: Pregnant women with labor pain who had cervical length <30 mm (45/161; 28%) went into delivery within 7 days, and women with a cervical length <15 mm (11/14; 79%) went into delivery within 7 days. When the PAMG-1 test result was positive and cervical length was <= 15 mm, the positive predictive value (PPV) was 83%; and when cervical length was <= 30 mm the PPV was 69%. The optimal cut off from receiver operating characteristic curve analysis showed that a cervical length <25 mm and PAMG-1 positive result has a PPV of 80% to predict preterm birth within 7 days and 90% within 14 days. The area under the curve (95% confidence interval) for a positive PAMG-1 result and cervical length <= 25 mm to predict preterm birth <7 days was 0.61 (0.50, 0.73) and <14 days was 0.60 (0.49, 0.70). Conclusions: Cervical length ranging 15-30 mm combined with a positive PAMG-1 test result has a high accuracy to predict imminent spontaneous delivery within 7 days by women with preterm labor and cervical dilatation <3 cm in clinical practice.