The neutrophil-to-lymphocyte ratio: A low-cost antenatal indicator of placental chorioamnionitis in women who deliver preterm without clinical signs and symptoms of infection.

Unlabelled: Chorioamnionitis is present in up to 70% of spontaneous preterm births and is associated with poor maternal, fetal and neonatal outcomes.

Objective: To explore the relationship between the neutrophil-to-lymphocyte ratio and histological chorioamnionitis in women who delivered preterm with no clinical signs or symptoms of infection.

Study Design: This was a retrospective analysis of a cohort of women who delivered spontaneously between 16 and 36 weeks at a tertiary UK hospital. Only women with placental histology and no signs of clinical infection were included. The neutrophil-to-lymphocyte ratio was calculated from a full blood count sample taken routinely within 24 h of delivery. The neutrophil-to-lymphocyte ratio was also calculated from first trimester booking bloods (<13 + 6 weeks) in a subgroup. Placental histopathology was categorised as either inflammatory (i.e. histologic chorioamnionitis, with or without evidence of fetal inflammatory response) or non-inflammatory (vascular pathology or a normal placenta).

Results: 169 women had available placental pathology and were included in the analysis. 70 % (118/169) had confirmed placental inflammation. The mean neutrophil-to-lymphocyte ratio was significantly raised in this group compared to those with normal (n = 24) or vascular (n = 27) pathology (inflammatory neutrophil-to-lymphocyte ratio 9.81 vs non-inflammatory neutrophil-to-lymphocyte ratio 6.53, p = 0.002. The delivery neutrophil-to-lymphocyte ratio had an area under the receiver operating characteristic curve of 0.69 (0.60 to 0.78) for predicting placental inflammation. A raised neutrophil-to-lymphocyte ratio (>6) was associated with an odds ratio of 5.2 (95 % CI 2.55 to 10.56) for histological chorioamnionitis, with a sensitivity of 80 % and negative predictive value of 86 %. A higher cut-off of 9 had a negative predictive value of 79 % for fetal inflammatory response.

Conclusions: A raised neutrophil-to-lymphocyte ratio is associated with a 5-fold increased risk of histological chorioamnionitis in women who delivered early without signs or symptoms of infection. It was also raised at the time of preterm labour compared to the first trimester. A full blood count is an almost universal investigation in women admitted in preterm labour, often repeated, making this inexpensive and non-invasive ratio a useful additional antenatal biomarker in women admitted in spontaneous preterm labour at risk of subclinical chorioamnionitis and its associated poor outcomes.