Tumour necrosis factor inhibitor use during pregnancy is associated with increased birth weight of rheumatoid arthritis patients' offspring.

OBJECTIVES: To study pregnancy outcomes in a closely monitored, well-defined cohort of women with rheumatoid arthritis (RA). In particular, pregnancy outcomes of women that used a TNFi during pregnancy.

METHODS: Patients were derived from a prospective study on pregnancy and RA (Preconception Counseling in Active RA study) and treated according to a treatment protocol aimed at minimal disease activity. Multivariate linear regression analysis was used to describe which variables influenced birth weight.

RESULTS: 188 patients were included, 92 (48.9%) patients with RA used a TNFi during pregnancy. Disease Activity Score in 28 joints C reactive protein (DAS28CRP) was low at all time points during pregnancy (DAS28CRP in the third trimester: 2.17 (SD 0.73). TNFi use was not associated with an increase of adverse pregnancy outcomes such as low birth weight (<2500 g), (emergency) caesarian section, hypertensive disorders or congenital malformations. TNFi use resulted in less children born small-for-gestational age (p=0.05), however, did not increase the risk of large-for-gestational age (p=0.73). Mean birth weight was 173 g higher in women that used a TNFi during pregnancy (3.344 kg vs 3.171 kg, p=0.03). In the multivariate analysis, maternal age (β -0.023, 95% CI -0.040 to -0.0065, p=0.007), TNFi use (β 0.20, 95% CI 0.066, 0.34, p=0.004), diabetes mellitus (β 0.37, 95% CI 0.12, 0.63, p=0.004) and gestational age (β 0.18, 95% CI 0.15, 0.2, p<0.001) were statistically significant associated with birth weight.

CONCLUSIONS: This is the first study to show that TNFi use during pregnancy is associated with increased birth weight of offspring of women with well-controlled RA. The underlying mechanism of TNF-inhibition on birth weight and the long-term consequences for the offspring should be explored in future research.