By linking two Norwegian national data registries, investigators confirmed previous findings that the incidence of rheumatoid arthritis is increased in women in the 2 years following delivery, compared with the subsequent 2 years post partum.
The results also showed an elevated incidence of other chronic arthritides in the first 2 postpartum years, said Dr. Marianne Wallenius of the department of rheumatology at St. Olav's Hospital in Trondheim, Norway, and her colleagues.
The impact of studies like that of Dr. Wallenius and her colleagues “goes beyond the field of rheumatologists interested in female health issues, but these studies may contribute to a better understanding of the fundamental question why one person gets RA and another does not,” noted Dr. Radboud J.E.M. Dolhain of Erasmus University Medical Centre, Rotterdam, the Netherlands, in an accompanying editorial (Ann. Rheum. Dis. 2010;69:317-8).
One hypothesis is that pregnancy exerts a protective effect on RA and other arthritides, which then disappears after delivery, allowing disease to flare. But this study did not look at incidence during pregnancy. More epidemiologic data are needed “to determine whether this is a true increased incidence or whether rather the incidence of RA and other forms of arthritis is postponed to after delivery,” Dr. Dolhain said.
The investigators linked data from a registry of people with inflammatory arthropathies who were taking disease-modifying antirheumatic drugs (the NOR-DMARD Registry) with the Medical Birth Registry of Norway that has recorded all births in Norway since 1967. They were able to locate 293 women with arthritis whose disease was first diagnosed after delivery. Of these, 183 were diagnosed with RA and 110 with other chronic arthritides (OCA), including 51 with psoriatic arthritis, 14 with ankylosing spondylitides and 45 with unspecified arthritis.
Of those with RA, 38% (69 women) were diagnosed in the first 2 years post partum, compared with 28% (31 women) who were diagnosed with OCA. The incidence of disease peaked in the first 2 years after pregnancy, compared with the subsequent 2 years for those who were diagnosed solely with RA (incident rate ratio, 1.73) or for the entire RA-plus-OCA group (IRR, 1.44) after all pregnancies were considered, but not for those who were diagnosed only with OCA (IRR, 1.05) (Ann. Rheum. Dis. 2010;69:332-6).
Disclosures: Research was supported by the liaison committee between the Central Norway Regional Health Authority and the Norwegian University of Science and Technology. The NOR-DMARD registry is supported by all makers of biologic drugs for RA in Europe.