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Objectives Adverse Pregnancy Outcomes (APO) are more common in patients with systemic lupus erythematosus (SLE). The neutrophil-to-lymphocyte ratio (NLR) is a simple biomarker that reflects systemic inflammation and has prognostic value in cardiovascular disease and cancer. We aim to evaluate its utility to predict late APOs in pregnant women with SLE.Methods A retrospective, observational, single-centre study was conducted. We searched for pregnancies in SLE female patients between 2010 and 2024. Demographic, clinical and laboratory data were obtained from Electronic Health Records. Late APOs included hypertensive disorders of pregnancy, preterm delivery, intrauterine growth restriction and puerperal haemorrhage. Late delivery, intrahepatic cholestasis and first trimester miscarriages were excluded from analysis. NLR formula is neutrophil divided by lymphocyte counts. Other inflammation indices, namely SII (NLR x Platelet count) and SIRI (NLR x Monocyte count) were calculated. Blood cell counts from first and second trimester (up to week 28) were used. All statistical analyses were performed using R programming language.Results A total of 43 pregnancies in SLE patients were identified in our registry. Late APOs were present in 10 patients (24%). Laboratory data from the first two trimesters of pregnancy were only available for 33 patients and their values across APO and non-APO groups are shown in table 1. As expected, week of delivery and birth weight were lower for the APO group. On average, NLR tends to be higher in the APO group (4.3 vs 3.2; p = 0.5) but not statistically significant. Overall, we found no statistically significant differences in the mean count of white blood cells (WBC) or their ratios (NLR, SII, SIRI) between the APO and non-APO groups.Abstract PO:08:200 Table 1APLA: Anti-Phospholipid Antibodies; NLR: Neutrophil-to- lymphocyte Ratio; SII: Systemic Inflammation Index; SIRI: Systemic Inflammation Response Index.Conclusions First and second trimester mean WBC count and their ratios (NLR, SII and SIRI) were not different among SLE patients who experienced late APOs and those who did not. WBC counts are highly variable through pregnancy and are influenced by multiple factors, so their utility for the prediction of APO may be limited. Of note, our results are limited by the reduced sample size and the low number of late APOs.