<b><i>Purpose:</i></b> The purpose of this study was to investigate a possible relationship between systemic inflammatory markers such as neutrophil-lymphocyte ratio (NLR), platelet-lymphocyte ratio (PLR), lymphocyte monocyte ratio (LMR), threatened preterm labor (TPL), and preterm premature rupture of membranes (PPROM), using complete blood cell count (CBC) parameters. <b><i>Method:</i></b> The study was carried out prospectively with patients admitted to our university hospital due to preterm labor and at risk of PPROM. The cases were divided into three groups according to their pregnancy status. Group 1 consisted of 90 patients with PPROM between 24th and 36th gestational weeks; group 2, 115 patients diagnosed with TPL between 24th and 36th gestational weeks; group 3, 101 patients over 36 weeks of gestation (control) who were not in labor. In addition to the demographic data of the patients, CBC parameters (white blood cell (WBC), Hg, Hct, Plt, lymphocyte, monocyte, mean platelet volume, PLR, LMR, and NLR) and C-reactive protein (CRP) values were examined and compared in each of the three groups. <b><i>Results:</i></b> CRP and WBC values of group 1 (PPROM) were higher than group 2 (TPL) and group 3 (control) (<i>p</i> < 0.05 for both). Pearson correlation between the gestational age and PLR and NLR values was significant (<i>r</i> and <i>p</i> values for PLR and NLR, respectively, <i>r</i> = −0.18, <i>p</i> < 0.001; <i>r</i> = −0.23, <i>p</i> < 0.001). However, there was no significant difference between the groups regarding PLR, NLR, LMR, platelet, monocytes, and lymphocyte counts. <b><i>Conclusions:</i></b> Only WBC was a valuable parameter in predicting preterm labor and PPROM. Although there was no significant difference between the groups in PLR and NLR, a negative correlation was found with gestational age at delivery. CRP value is still a helpful parameter in PPROM and TPL prediction.
