Purpose: We aimed to analyze the linear changes of Neutrophil-to-Lymphocyte Ratio (NLR), Platelet-to-Lymphocyte Ratio (PLR) and Systemic Immune-Inflammation Index (SII) levels in pregnant women who administrated magnesium sulfate for fetal neuroprotection. Methods: This retrospective study included 63 pregnant women who underwent neuroprotective magnesium sulfate administration during January 2015 and July 2020. Women with co-existing diseases or obstetric complications such as preeclampsia, gestational diabetes mellitus, suspicion of chorioamnionitis etc. excluded. The laboratory test results were obtained for each participant. Three results were compared; (1) Before magnesium sulfate-0th hour, (2) 6 h and (3) 12 h after starting loading dose. Results: The mean NLR was 7.18 ± 5.14 in patients before treatment. The mean NLR increased to 10.09 ± 4.77 and 10.04 ± 4.35 at 6th and 12th hour of magnesium sulfate treatment. The mean PLR was also increased after starting neuroprotective magnesium sulfate (170.35 ± 89.09 at the beginning; 209.85 ± 88.77 at 6th hour and 209.24 ± 76.66 at 12th hour). The mean SII was found to be increased from 1783.33 ± 1367.29 to 2517.15 ± 1325.77 with magnesium sulfate treatment. However, no statistically significant difference was observed in terms of SII between 6 and 12th hours of treatment (p = 0.752). Maternal serum magnesium levels at 6th and 12th hour were found to be not correlated with NLR, PLR and SII. Conclusion: We demonstrated that values of NLR, PLR and SII at 6th hour were all increased after starting magnesium sulfate. Levels of these systemic inflammatory indices were similar at 6th and 12th hour of therapy.