The difference in performance of RADAI and DAS28 during pregnancy might explain discrepancies between older and more recent studies on the impact of pregnancy on rheumatoid arthritis

Background/Purpose: Pregnancy is the only condition in which Rheumatoid Arthritis(RA) shows spontaneous remission. Old and recent studies showed improvement of disease activity, which was more pronounced and occurred earlier in pregnancy in older studies. A possible explanation is self-assessed retrospective(old) to prospective jointscore(recent) measurements. The Disease Activity Score in 28 joints(DAS28) and self-assessed Rheumatoid Arthritis Disease Activity Index(RADAI) are valid tools to determine disease activity in RA. However the influence of pregnancy on RADAI scores and the association of the RADAI with pregnancy outcome has not been determined. Insight may contribute to a better understanding of differences in outcome between older and recent studies. Should the RADAI be a valid instrument during pregnancy, it could be used for studies on RA and pregnancy. The aim of this study is to determine the validity of the RADAI during pregnancy in patients with RA by determining the correlation and agreement of the RADAI to the DAS28 and to determine the association between the RADAI and pregnancy outcome. Methods: Pregnant RA patients were visited at their home-address (once before conception, during every trimester and three times post partum). During these visits disease activity was measured by RADAI and DAS28 and birthweight was recorded. Correlations were determined for each time point. Furthermore, patients were stratified according to three disease states (high, intermediate, low/remission combined) based upon DAS28 and RADAI. Finally, the association between birthweight and disease activity, measured both by DAS28 and RADAI, was determined. Results: Disease activity determined by RADAI and DAS28 showed a decrease during pregnancy and a flare after delivery(p<0.01). The correlations between RADAI and DAS28 were good (pre conception rho=0.49, all other time points 0.61<rho<0.71(p<0.01). Patients stratification according to disease state showed, according to the RADAI, more patients in remission/ low disease activity during the 1st trimester. (1sttrim.RADAI 42,1%;DAS28 26.3%p=0.01), whereas during the 3rd trimester these percentages were comparable (RADAI 43.3%;DAS28 41.3%p=0.12). After delivery both observed the highest disease activity at 12 weeks after delivery. Despite this, agreement on the disease activity states was low(0.28<kappa<0.51). The association between disease activity and birthweight was significant when the DAS28 was used (DAS28p=0.04; RADAIp=0.07). Conclusion: To determine disease activity in pregnant patients with RA and to predict pregnancy outcome, the DAS28 is recommended over the RADAI. Differences in performance of DAS28 and RADAI during pregnancy in RA patients might explain discrepancies between older and recent studies on the impact of pregnancy on RA