The neutrophil-to-lymphocyte ratio: a marker for microbial invasion of the amniotic cavity in preterm prelabor rupture of membranes

Objective: This study investigated the relationship between maternal blood neutrophil-to-lymphocyte ratio (NLR), serum C-reactive protein (CRP) levels, and microbial invasion of the amniotic cavity (MIAC) in the context of preterm prelabor rupture of membranes (pPROM). Methods: This retrospective cohort study included 154 women with pPROM between 20+0 and 33+6 weeks of gestation who underwent transabdominal amniocentesis. MIAC was defined as a positive amniotic fluid culture. Maternal blood samples were collected within 24 hours after amniocentesis. CRP levels and leukocyte differential counts were quantified. Results: MIAC was diagnosed in 36.4% of the patients with pPROM. Patients with MIAC had significantly higher median NLR and CRP levels than those without MIAC (NLR, 6.8 vs. 5.0; CRP, 0.58 mg/dL vs. 0.26 mg/dL, both P<0.05). NLR and CRP exhibited comparable areas under the curve 0.67 (95% confidence interval [CI], 0.58-0.75) vs. 0.63 (95% CI, 0.54-0.72); P=0.59. Receiver operating characteristic curve analysis was performed to establish the most effective diagnostic cutoff values for NLR and CRP (6.2 for NLR and 0.7 mg/dL for CRP). The prevalence of MIAC was highest in patients with both elevated NLR and CRP levels (54.3%) and lowest in those with low values of both parameters (18.8%). Intermediate prevalence rates were observed in patients with discordant NLR and CRP values. Conclusion: NLR exhibited a significant positive association with MIAC in patients with pPROM, with a diagnostic performance similar to that of CRP. Nonetheless, the presence of MIAC in 18.8% of the patients with low levels of both parameters highlights the limitations of these measures in ruling out MIAC.