Bandoli G, Singh S, Strouse J, et al. - Through a California birth cohort created from linked birth certificates and hospital discharge summaries of 2,963,888 births and women with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), psoriasis and inflammatory bowel disease (IBD), researchers quantified the mediated impacts of autoimmune conditions on adverse pregnancy outcomes. All four autoimmune diseases were correlated with preterm birth and cesarean delivery, and RA, SLE, and IBD were related to small for gestational age offspring. Preeclampsia/hypertension was the most powerful mediator of RA, SLE, and psoriasis, accounting for 20-33% and 10-19% of the excess risk of preterm births and excess cesarean deliveries. Gestational diabetes and infections usually mediated < 10% of excess adverse pregnancy outcomes. Among women with IBD, selected pregnancy complications mediated the smallest amount of adverse pregnancy outcomes out of the four autoimmune conditions. Therefore, some excess risk of adverse pregnancy outcomes was mediated through pregnancy complications, especially preeclampsia/hypertension. Moreover, quantifying excess risk and related pathways gave insight into the underlying etiologies of adverse pregnancy outcomes and could notify intervention approaches.