The aim of the study was to investigate peripheral blood platelets, neutrophils and lymphocytes counts in women with preterm premature rupture of membranes (PPROM) and threatened preterm labour (TPL) compared with gestation-matched controls in order to learn how they change. This study was conducted on 60 women with PPROM, 50 women with TPL and 47 healthy pregnant women. Laboratory parameters (including complete blood count, C-reactive protein (CRP)) of all the participants were recorded. The neutrophil-to-lymphocyte ratio (NLR) values were significantly higher in PPROM group than TPL group and healthy control group (6.1 +/- 3.9, 4.4 +/- 1.7, 4.4 +/- 2.2, p = .007, p = .018, respectively). At a cut-off level of 5.14, NLR accurately predicted occurrence of neonatal sepsis (AUC = 0.717 (95% confidence interval 0.610-0.824), p = .001) with sensitivity and specificity rates of 69.7% and 72.0%, respectively. In the management of the patients with PPROM, NLR can be used as a more cost-effective method than other blood parameters that require the use of a kit.IMPACT STATEMENT What is already known on this subject? There is only one study in the literature evaluating blood count parameters (such as platelet-to-lymphocyte ratio (PLR), NLR) in PPROM pregnancies. That study demonstrated PLR and NLR were both higher in the PPROM group. What do the results of this study add? The present study demonstrates that only NLR is higher in the PPROM group. Furthermore, we have also demonstrated distinctively that NLR can predict occurrence of neonatal sepsis.