Fetal growth and preterm birth in offspring of parents with rheumatoid arthritis. A Danish cohort study

INTRODUCTION:  Maternal rheumatic diseases including Rheumatoid arthritis (RA) are found to be associated with a range of adverse pregnancy outcomes. Fewer studies investigated pregnancy outcomes among mothers diagnosed with RA exclusively. Furthermore, some indicators of fetal growth are sparsely examined in offspring of mothers with rheumatic diseases. Indicators of fetal growth are found to be associated with adverse health outcomes in the long term. Thus, the objective of this study was to asses indicators of fetal growth and risk of preterm birth in offspring of parents with RA.

METHODS:  A Nationwide cohort study including 1 917 723 singletons born in Denmark from 1977 to 2008 was conducted through linkage of Danish national registers. General linear regression models were used to estimate fetal growth in offspring of parents with RA. By a logistic regression model, odds ratio (OR) for preterm birth (<37 weeks) was calculated in offspring of parents with RA, compared to offspring of parents without RA. We adjusted for age, parity, education, smoking, country of origin and birth year.

RESULTS:  A total of 2101 (0.11%) children were exposed to maternal RA diagnosed prior to birth. Offspring of mothers diagnosed with RA prior to birth had approximately similar head and abdominal circumference, compared with unexposed children. Birth weight was slightly reduced by 87 gram (-87.04 g; 95% CI, -111.23;-62.84) and weight of placenta was reduced by 14 gram (-13.45 g; 95% CI, -21.46;-5.43).  Similar results were found in offspring of mothers diagnosed with RA after birth and no associations were found with paternal RA. Compared with unexposed children, risk of preterm birth was increased in offspring of mothers diagnosed with RA (OR, 1.48; 95% CI,1.20;1.84).  

CONCLUSIONS:  Even though children exposed to maternal RA more often are born preterm, indicators of fetal growth were only slightly reduced, compared to unexposed children.