The Association of Inflammatory Biomarker of Neutrophil-to-Lymphocyte Ratio with Spontaneous Preterm Delivery: A Systematic Review and Meta-analysis

Background Neutrophil-to-lymphocyte ratio (NLR), as an inflammatory biomarker, has been investigated in several studies for early prediction of preterm delivery. However, their findings seem to be controversial. Thus, this systematic review and meta-analysis was conducted to evaluate the role of NLR in predicting preterm delivery as compared to term controls.Methods PubMed, Web of Science, Embase, Scopus, and Google Scholar were systematically searched from inception up to December 2020. Interstudy heterogeneity was assessed using Cochrane's Q test and the I 2 statistic. The random-effects model was employed to pool the weighted mean differences (WMDs) and the corresponding 95% confidence intervals (CIs).Results Out of a total of 4369 recodes, fifteen articles including 3327 participants were enrolled. The meta-analysis finding using the random-effects model produced a pooled estimate suggesting a significantly higher NLR (WMD = 1.23, 95% CI: 0.40–2.07) in women with preterm delivery ( P = 0.01). We found significant heterogeneity across the included studies ( P < 0.001, I 2 = 92.33%). However, interstudy heterogeneity exists mainly due to differences in the definition of preterm delivery ( I 2 = 0.0%). In the metaregression analysis, there was no significant effect of publication year ( B = −0.288, P = 0.088), total sample size ( B = −0.002, P = 0.276), and the mean age of cases ( B = −0.06, P = 0.692) on the association between NLR and preterm delivery.Conclusion The results of this meta-analysis revealed that the NLR value is higher in patients with preterm delivery. The NLR could be a useful biomarker for predicting preterm delivery; however, further prospective case-control studies are required to produce stronger evidence.