Children born to mothers with rheumatoid arthritis are more likely to be born prematurely and have a lower birth weight than are those born to mothers without the condition, according to a Danish nationwide cohort study.

The reduction in fetal growth, however, is small – a mean difference of 87 g – and unlikely to have any impact on the well being of the child, Ane Rom of Copenhagen University Hospital and her colleagues reported in Arthritis & Rheumatology.

Of 1,917,723 children born in Denmark during 1977-2008, 13,556 children were exposed to either maternal or preclinical RA. Children with mothers who had rheumatoid arthritis (RA) were almost one and half times more likely (odds ratio, 1.48; 95% confidence interval, 1.20-1.84) to be born preterm. The odds of preterm birth were slightly lower, but still elevated, in children with mothers who had preclinical signs of disease, compared with children not exposed to RA (OR, 1.32; 95% CI, 1.07-1.64).

Children exposed to RA had a similar length and head and abdominal circumference at birth, compared with children of mothers without RA, but their birth weight was, on average, 87 g lower (95% CI, –111.23 to –62.84) and their placenta weight was 14 g lower (95% CI, –21.46 to –5.43). The investigators found similar results for children exposed to preclinical RA (Arthritis Rheumatol. 2014 Nov. 13 [ doi:10.1002/art.38874 ]).

Paternal RA was not associated with reduced fetal growth or preterm birth. Maternal RA may affect fetal growth either through fetal programming related to the effect that RA may have on the intrauterine environment, through genetic factors, or through medications taken in pregnancy. “For women with RA, it is reassuring that only a small reduction in fetal growth was found for most of their children, which will have little, if any, impact on perinatal conditions for the child,” Ms. Rom and her associates wrote.

“Clinicians should be aware of the increased risk of preterm birth not only in women diagnosed with RA but also in women with signs of preclinical RA,” they concluded.

Ms. Rom’s work on the study was supported by grants from the National Institutes of Health, the Danish Council for Independent Research, and the Augustinus Foundation. No conflicts of interest were reported.