No Effect on Infant Birth Weight and Head Circumference After Exposure to Interferon Beta Prior to Or During Pregnancy: A Register-Based Cohort Study in Finland and Sweden Among Women with Multiple Sclerosis

Women with multiple sclerosis (MS) are in most cases diagnosed and treated at childbearing age. Some studies with limited sample size suggested that MS and interferon-beta (IFNβ) exposure might affect birth weight and head circumference. Prevalence of these two measures at birth was determined in IFNβ-exposed and unexposed pregnant women with MS from health registers in Finland and Sweden. Health register data from Finland (1996-2014) and Sweden (2005-2014) were used to study women with MS: 1)dispensed only IFNβ within 6-months prior to date of last menstrual period or during pregnancy (IFNβ-exposed) and 2)without any dispensed MS disease modifying drugs (unexposed). Prevalence (95% confidence interval [CI]) of the following birth outcomes was described for IFNβ-exposed and unexposed women: low birth weight for live births (<2500g), low head circumference for infants with full-term live birth (≥37 gestational weeks) and small or large for gestational age (SGA and LGA respectively). For SGA, LGA, and head circumference, national gestational age and sex-specific national references were used. No adjustments for potential confounding factors were performed. Among 666 IFNβ-exposed and 1330 unexposed live births, the prevalence of birth outcomes was similar between IFNβ-exposed vs unexposed. Prevalence of low birth weight (95%CI) was 3.9%(2.6-5.7) among IFNβ-exposed and 4.8%(3.7-6.1) among unexposed live births. Among 619 IFNβ-exposed and 1219 unexposed full-term live births, prevalence of low head circumference (95%CI) was 1.9%(1.0-3.4) vs 1.1%(0.6-1.8) respectively. Comparing the IFNβ-exposed vs unexposed, SGA (95%CI) was 2.1%(1.2-3.5) vs 2.0%(1.3-2.9), and LGA (95%CI) was 0.8%(0.2-1.7) vs 0.8%(0.4-1.5). Data from Finnish and Swedish health registers showed no evidence that IFNβ exposure before and during pregnancy affected infant birth weight and head circumference.