Prediction of postpartum onset of rheumatoid arthritis.

OBJECTIVE To investigate the prediction of the postpartum onset of rheumatoid arthritis (RA). METHODS Two thousand five hundred and forty seven healthy pregnant subjects were examined prospectively and the relation between serum rheumatoid factors (RF) and postpartum onset of RA was observed. Rheumatoid factors were measured in early pregnancy by the antihuman IgG latex agglutination test (Latex test) and antirabbit IgG haemagglutination test (RAHA test). RESULTS Latex test and RAHA test were positive in 26 (1.0%) and 64 (2.5%) pregnant subjects, respectively. Four hundred and ten subjects of 2547 pregnant women could be followed up for one year after delivery. None of 401 subjects without RF, or with only one RF on either Latex test or RAHA test, developed RA after delivery. Two (22.2%) of nine subjects with both RFs developed RA at one and three months postpartum, respectively. Transient arthralgia was found within 12 months postpartum in three of nine (33.3%) subjects with both RFs and this prevalence was significantly higher than that in RF negative subjects (8.1%). CONCLUSION Postpartum onset of RA was found in at least 2 of 2547 healthy subjects (0.08%) and onset was predicted by positive test for rheumatoid factors.