Preterm birth in women with psoriatic arthritis: what are the risks and risk factors? A collaborative cohort study from Sweden, Denmark and Norway

OBJECTIVE: To estimate risk and to identify risk factors for preterm birth in pregnant women with psoriatic arthritis (PsA) in relation to maternal characteristics, treatment and disease activity, both before and during pregnancy.

METHODS: We linked clinical rheumatology registers to medical birth registers in Sweden, Denmark and Norway and identified PsA pregnancies and control pregnancies 2006-2021, matched 1:10 on age, parity, country and birth year. Adjusted ORs (aORs) for preterm birth in PsA pregnancies vs control pregnancies were calculated overall and stratified by maternal characteristics, antirheumatic treatment and disease load (9 months before and during pregnancy).

RESULTS: We observed 54 preterm births among 688 PsA pregnancies (7.8%) versus 312 among 6880 control pregnancies (4.5%); aOR, 95% CI: 1.80, 1.29 to 2.51. The risk estimate was largely unaffected by parity, smoking and body mass index. PsA pregnancies exposed to a combination of biologic and conventional synthetic disease-modifying antirheumatic drugs (DMARDs) and/or glucocorticoids during pregnancy had a markedly increased risk of preterm birth compared with control pregnancies (4.44, 2.07 to 9.50), whereas exposure to biological DMARD (bDMARD) monotherapy (primarily tumour necrosis factor inhibitors) had not (0.73, 0.22 to 2.42). High disease load before pregnancy was associated with increased risk. The proportion of preterm birth was higher in those stopping bDMARD during the first trimester (21%) opposed to those continuing past the first trimester (10%) based on few events.

CONCLUSION: We identified an 80% increased risk of preterm birth in PsA pregnancies compared with control pregnancies. Antirheumatic combination therapy during and high disease load before pregnancy constituted risk factors. Discontinuing bDMARD treatment in early pregnancy further increased the risk. Our findings support that a subgroup of PsA pregnancies should be considered high-risk pregnancies.