ABSTRACT: Intrauterine growth restriction complicates 5-10% of pregnancies. This study aims to test the hypothesis that Chinese herbal formula, JLFC01, affects pregnancy and fetal development by modulating the pro-inflammatory decidual micro-environment.Human decidua from gestational age-matched elective terminations or incomplete/missed abortion was immunostained using anti-CD68 + anti-CD86 or anti-CD163 antibodies. qRT-PCR and Luminex assay measured the effects of JLFC01 on IL-1?- or TNF-?-induced cytokine expression in first trimester decidual cells and on an established spontaneous abortion/intrauterine growth restriction (SA/IUGR)-prone mouse placentae. The effect of JLFC01 on human endometrial endothelial cell angiogenesis was evaluated by average area, length and numbers of branching points of tube formation. Food intake, litter size, fetal weight, placental weight and resorption rate were recorded in SA/IUGR-prone mouse treated with JLFC01. qRT-PCR, Western blot and immunohistochemistry assessed the expression of mouse placental IGF-I and IGF-IR.In spontaneous abortion, numbers of decidual macrophages expressing CD86 and CD163 are increased and decreased, respectively. JLFC01 reduces IL-1?- or TNF-?-induced GM-CSF, M-CSF, C-C motif ligand 2 (CCL2), interferon-?-inducible protein-10 (IP-10), CCL5 and IL-8 production in first trimester decidual cells. JLFC01 suppresses the activity of IL-1?- or TNF-?-treated first trimester decidual cells in enhancing macrophage-inhibited angiogenesis. In SA/IUGR-prone mice, JLFC01 increases maternal food intake, litter size, fetal and placental weight, and reduces fetal resorption rate. JLFC01 induces IGF-I and IGF-IR expression and inhibits M-CSF, CCL2, CCL5, CCL11, CCL3 and G-CSF expression in the placentae.JLFC01 improves gestation by inhibiting decidual inflammation, enhancing angiogenesis and promoting fetal growth.