Objective The immune checkpoint inhibitor, membrane-bound T cell immunoglobulin mucin domain 3 (Tim-3), binds to galectin-9 (gal-9) and promotes immune tolerance during pregnancy. Soluble Tim-3 (sTim-3) competes with Tim-3 for binding to gal-9 and modulates its activity. Our objective was to evaluate the influence of sTim-3 on immune responses and outcome in pregnant women. Study design Peripheral blood from 71 pregnant women was separated into mononuclear cell (PBMC) and plasma fractions. The PBMCs were lysed and tested for Tim-3 by ELISA. Plasma was assayed for sTim-3, gal-9, tumor necrosis factor-α (TNF-α), interleukin-10 (IL-10) and the stress-inducible 70 kDa heat shock protein (hsp70) by enzyme-linked immunosorbent assay (ELISA). Correlations were analyzed by the Spearman rank correlation test. Results The higher the sTim-3 level in plasma the lower was the PBMC Tim-3 concentration (p = .0135), suggesting that sTim-3 results from the release of membrane-bound Tim-3. Plasma sTim3 levels were positively correlated with levels of gal-9 (p < .0001), TNF-α (p = .0071) and hsp70 (p = .0144), but not with IL-10. The sTim-3 level was positively associated (p = .0276) with gestational age at delivery. There was no association between sTim-3 and gestational age at sample collection, maternal age, gravidity, parity or body mass index. Conclusion The release of Tim-3 from membranes and sTim-3 reacting with gal-9 may increase proinflammatory immunity and the stress response. The release of sTim-3 from lymphoid cells into the circulation and its binding to gal-9 may modulate Tim-3-mediated activity and help optimize immune regulation during pregnancy.