Women who suffer from rheumatoid arthritis (RA) or pre-clinical RA are 1.5 more likely to have their babies prematurely.

RA causes chronic inflammation of the joints and affects about 1 percent of people worldwide, Wiley reported. The condition, which was linked to preterm birth, is three times more prevalent in women than it is in men. 

In the past rheumatic diseases have been linked to pregnancy complications such as preterm birth and low birth weight in babies, but there has been limited evidence. The recent findings showed body measurements of babies born to mothers with RA were only marginally lower on average than those born to women without the condition.

To make their findings the researchers looked at Denmark national registries of children born between the years of 1977 and 2008 and excluded for factors such as multiple child births and adoption until reaching a final sample of 1,917,723 children.

The results showed 13,566 children were exposed to maternal RA or preclinical RA (if the mother was diagnosed after birth). Compared with the children who were not exposed to RA the research team determined the early birth risk was higher in children exposed to maternal RA and pre-clinical RA with an odds ratio of 1.48 and 1.32, respectively. 

"Obstetricians should be aware of the increased risk of preterm birth in women with RA and among those with preclinical signs of the disease," said Ane Rom, from Copenhagen University Hospital in Denmark.

"For women with RA, we found only a small reduction in fetal growth in their babies, which has little impact on the children immediately following birth. The long term health effects for children born to mothers with RA need further investigation," Rom concluded.

The findings were published in a recent edition of the journal Arthritis & Rheumatology.