(1168) Peripheral blood inflammatory indices in early pregnancy are associated with preterm birth (PTB)

Although validated blood-based inflammatory indices are associated with clinical outcomes in other medical fields, they have not been widely studied in obstetrics. We sought to determine if 3 of these indices, the neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), and systemic immune-inflammation index (SII), are associated with PTB.


Study Design: Retrospective, observational cohort of patients with singleton gestations and CBC w/diff drawn for clinical care < 20 weeks’ gestation from a university health system, 2014-2021. Absolute peripheral platelet (P), neutrophil (N), and lymphocyte (L) counts were used to calculate the NLR (N/L), PLR (P/L), and SII (P*N/L). The primary outcome was PTB < 37 wks, regardless of indication. Indices were evaluated by quartile, with Q1 (lowest) as referent. Regression models estimated the relationship between PTB and (1) NLR; (2) PLR; and (3) SII. A prognostic nomogram was generated based on the best performing regression model.

Results:

3,606 patients met inclusion criteria; 49% delivered preterm < 37 weeks. Cohort characteristics are shown in Table 1. Mean SII values were higher among those with PTB (906 ± 547 vs. 852 ± 532, p=0.03), though mean NLR (3.4 ± 2.1 vs. 3.3 ± 1.9, p=0.127) and mean PLR (140 ± 65 vs. 136 ± 58, p=0.094) did not differ. In regression models, the adjusted odds of PTB was: (1) increased for NLR Q3 (aOR 1.34, 95% CI 1.02-1.78) and NLR Q4 (aOR 1.47, 95% CI 1.11-1.94); (2) not associated with PLR; (3) increased for SII Q4 (aOR 1.51, 95% CI 1.15-1.98). The NLR model performed best (AUC 0.67, 95%CI 0.65-0.70) and was used to create a prognostic nomogram (Figure 1).


Conclusion: Peripheral blood inflammatory indices can be calculated from routine prenatal labs (unlike markers such as CRP); elevation in early pregnancy confers an increased risk similar in magnitude to other known PTB risk factors. Analysis of mechanisms and trends across gestation may yield critical insight into novel therapies for PTB prevention.