587 - Association of Chronic Placental Inflammation and Increasing Gravity

Poster Number: 587
Publication Number: 587.135

Background: Chronic placental inflammation (CI) is characterized by chronic inflammatory cells, predominantly lymphocytes, histiocytes and plasma cells infiltrating the tissue compartments of the placenta. CI has been associated with adverse pregnancy outcomes, including intrauterine growth restriction and pregnancy loss. Two prevailing hypotheses for the etiology of chronic villitis, a specific lesion of CI, are an autoimmune response similar to allograft rejection and infection by an unidentified organism. Multigravid pregnancies have increased potential to undergo an autoimmune response and may have increased prevalence of CI.

Objective: To determine whether placentas of multigravid pregnant persons are more likely to have chronic inflammation than those of first pregnancies.

Design/Methods: Retrospective review of patients with delivery between 2017-2021 at NorthShore University HealthSystem with available placental pathology and gravidity. Placental histology was examined by an experienced placental pathologist and CI was categorized by standardized methods into none, low, and high grade. Infant and maternal characteristics were abstracted from the medical records. Chi squared, binary logistic regression, and ANOVA statistical tests were used for analysis.

Results: 6987 placentas were included - 1288 placentas had high grade CI, 2008 had low grade CI, and 3691 had no CI. Maternal gravida (G) ranged from 1 to 24 with a mean of 2.5 pregnancies. 4428 pregnancies were multigravid (G>1; 63%). Placentas of G>1 pregnancies had a significantly higher prevalence of high grade CI (21%) than those of G1 pregnancies (15%). Placentas of G>1 pregnancies had a significantly higher prevalence of either low or high grade CI (50%) compared to those of G1 pregnancies (43%) (Table 1). Using binary logistic regression, the odds ratio of having CI was 1.3 [1.2,1.5] with G>1 compared to first pregnancies. Infants exposed to placentas with increasing CI had increasingly lower birth weights. Gestational age was also lower for infants from placentas with CI compared to those from placentas without CI (Table 2).

Conclusion(s): We show multigravid pregnancies are more likely to be affected by CI, which may support the role of allograft rejection in the development of chronic placental inflammation. Further research is required to better understand the relationship/potential mechanism between multigravidity and maternal anti-fetal rejection to determine how this may relate to chronic placental inflammation.