Predictive performance of PAMG-1 vs fFN test for risk of spontaneous preterm birth in symptomatic women attending an emergency obstetric unit: retrospective cohort study.

OBJECTIVE

To compare the performance of the placental alpha microglobulin-1 (PAMG-1) and fetal fibronectin (fFN) tests for the prediction of spontaneous preterm delivery in patients presenting to an emergency obstetric unit with threatened preterm labor, by conducting a retrospective audit of patient medical records from separate 1-year periods during which either fFN or PAMG-1 was used as the standard-of-care biochemical test.

METHODS

This was a retrospective cohort study based on chart review of electronic medical records of women with threatened preterm labor presenting at a level-III maternity hospital over two different periods: (1) the 'baseline' period (year 2012), during which the qualitative fFN test with a cut-off of 50 ng/mL was used as the standard-of-care biochemical test for the risk assessment of preterm delivery, and (2) the 'comparative' period (year 2016), during which the PAMG-1 test with a cut-off of 1 ng/mL was used as the standard-of-care biomarker test. Patients with a singleton pregnancy between 24 + 0 and 34 + 6 weeks' gestation with symptoms of early preterm labor, clinically intact membranes and cervical dilatation < 3 cm, who did not have a medically indicated preterm delivery within 14 days of testing, were selected for chart review and included in the analysis. Key parameters used for the analysis were biochemical test results, time of testing and time of delivery. Positive predictive value (PPV), negative predictive value (NPV), sensitivity, specificity, and positive and negative likelihood ratios (LR+ and LR-) for the prediction of spontaneous preterm delivery ≤ 7 and ≤ 14 days of presentation were calculated for the PAMG-1 and fFN tests.

RESULTS

Four hundred and twenty patients were identified as having presented with threatened preterm labor during the baseline period, of whom 378 (90.0%) met the eligibility criteria. Of these, 38 (10.1%) were fFN positive and 10 (2.6%) had spontaneous preterm delivery ≤ 7 days of presentation. PPV, NPV, LR+ and LR- of fFN were 7.9%, 97.9%, 3.2 and 0.8, respectively, for spontaneous preterm delivery ≤ 7 days. Four hundred and ten patients were identified as having presented with threatened preterm labor during the comparative period and 367 (89.5%) subjects met the eligibility criteria. Of these, 17 (4.6%) were PAMG-1 positive and 12 (3.3%) had spontaneous preterm delivery ≤ 7 days of presentation. PAMG-1 PPV and NPV were 35.3% and 98.3%, respectively, and LR+ and LR- were 16.1 and 0.5, respectively, for spontaneous preterm delivery ≤ 7 days.

CONCLUSIONS

Before switching to PAMG-1, fFN was the standard-of-care test for the risk assessment of spontaneous preterm delivery. This retrospective audit of each test's performance over separate 1-year periods shows that we were more than twice as likely to get a positive fFN test than a positive PAMG-1 test, while the rate of discharging women who ultimately delivered spontaneously within 14 days of testing was not affected. Furthermore, a positive PAMG-1 test was more than four times more reliable than a positive fFN test in predicting imminent spontaneous preterm delivery. The use of a more reliable biomarker that is associated with fewer false-positive results could lead to a reduction in unnecessary admissions, interventions and use of hospital resources. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.