Data from a large-scale observational study of pregnant women with systemic inflammatory conditions (n = 4,961) shows that the risk of serious infection is similar among those taking steroids (3.4%), non-biologics (2.3%) or TNF inhibitors (1.5%). Comparisons between these groups found no statistically significant differences, giving hazard ratios for non-biologics versus steroids, TNF inhibitors versus steroids, and TNF inhibitors versus non-biologics of 0.81, 0.91 and 1.36, respectively. Dose–response analysis indicated that high steroid doses were independently associated with an increased risk of serious infection in pregnancy.