Pregnancy outcomes in women with idiopathic inflammatory myopathy, before and after diagnosis-a population-based study

Abstract

Objectives: To examine pregnancy outcomes among births to women with idiopathic inflammatory myopathy (IIM) in relation to time of IIM diagnosis using population-based data.

Methods: This study used Swedish nationwide registers to identify all singleton births that occurred between 1973 and 2016 among women diagnosed with IIM between 1998 and 2016 and among women unexposed to IIM. We classified births according to the IIM status of the mother at time of delivery: post-IIM (n = 68), 1-3 years pre-IIM (n = 23), >3 years pre-IIM (n = 710) and unexposed to IIM (n = 4101). Multivariate regression models were used to estimate relative risks of adverse pregnancy outcomes in post-IIM births and pre-IIM births separately, in comparison with their non-IIM comparators.

Results: We found that post-IIM births had increased risks of caesarean section [adjusted relative risk (aRR) = 1.98; 95% CI: 1.08, 3.64], preterm birth (aRR = 3.35; 95% CI: 1.28, 8.73) and low birth weight (aRR = 5.69; 95% CI: 1.84, 17.55) compared with non-IIM comparators. We also noticed higher frequencies of caesarean section and instrumental delivery in 1-3 years pre-IIM births than in the non-IIM comparators.

Conclusion: Women who gave birth after IIM diagnosis had higher risks of caesarean section, preterm birth and low birth weight. These results further underline the importance of special care and close monitoring of women with IIM. Higher frequencies of caesarean section and instrumental delivery in pre-IIM births highlight the need for future research on the influence of subclinical features of IIM on pregnancy outcomes.

Keywords: adverse pregnancy outcomes; caesarean section; idiopathic inflammatory myopathy; low birth weight; preterm birth.

Fig. 1

Flow chart of the study population Linkage to the Swedish Medical Birth Register for birth history in women with IIM identified from the National Patient Register and women unexposed to IIM randomly sampled from the Total Population Register. ^aA hospitalization indicating incident IIM. ^bDiagnosis of incident IIM with at least one follow-up visit within 1–12 months after the first IIM indication. ^cAdministrative error; comparators were kept in the study. IIM: idiopathic inflammatory myopathies.