Evaluation of the pregnancy prolongation index (PPI) as a measure of success of obstetric interventions in the prevention of preterm birth and associated morbidities

Abstract

This study was undertaken to evaluate the validity of the pregnancy prolongation index (PPI) as a measure of preterm labor treatment success. Analysis of prospectively collected maternal and neonatal data from a national clinical database (Matria Healthcare). Included were patients with singleton, twin, and triplet pregnancies who had outpatient surveillance initiated between 18 and 34 weeks and delivered at 24 to 36 6/7 weeks' gestation with NICU admission. Each patient's PPI score was calculated via the following equation: [(gestational age at delivery - gestational age at start of treatment) / (37.0 - gestational age at start of treatment)] x 100%. The impact of increasing PPI score was measured against NICU length of stay as a surrogate gauge of neonatal morbidity. Data were further stratified by gestational type and reason for delivery. Pregnancy outcomes of 12,642 patients (6,642 singletons, 4,326 twins, and 1,674 triplets) were analyzed. The PPI score increased in a direct, inverse linear relationship with decreasing number of NICU days. The PPI is a sensitive measure for the evaluation of treatment success in the inhibition of preterm labor and delivery.