Pregnancy requires a special management in women with inflammatory rheumatic diseases (RDs), with the aim of controlling maternal disease activity and avoiding fetal complications. Despite the heterogeneous course of RDs during pregnancy, their impact on pregnancy largely relates to the extent of active inflammation at the time of conception. Therefore, accurate evaluation of disease activity is crucial for the best management of pregnant patients. Nevertheless, there are limitations in using conventional measures of disease activity in pregnancy, as some items included in these instruments can be biased by symptoms or by physiological changes related to pregnancy and the pregnancy itself may influence laboratory parameters used to assess disease activity. This article aims to summarize the current literature about the available instruments to measure disease activity during pregnancy in RDs. Systemic lupus erythematosus is the only disease with instruments that have been modified to account for several adaptations which might interfere with the attribution of signs or symptoms to disease activity during pregnancy. No modified-pregnancy indices exist for women affected by other RDs, but standard indices have been applied to pregnant patients. The current body of knowledge shows that the physiologic changes that occur during pregnancy need to be either adapted from existing instruments or developed to improve the management of pregnant women with RDs. Standardized instruments to assess disease activity during pregnancy would be helpful not only for clinical practice but also for research purposes.