598: The effect of maternal autoimmune disease on fetal thymus size in the mid-trimester

Abstract

OBJECTIVE: Women with autoimmune disease (AD) have higher rates of adverse pregnancy outcomes. Smaller fetal thymus size is associated with pregnancy complications and correlates with increased Tregulatory cells in cord blood. This suggests a link between thymus development and immune status at birth. Anti-Tumor Necrosis Factor (TNF) drugs for AD modulate the maternal immune system. The TT-ratio, a previously described quotient of the anterior-posterior thymic and the intrathoracic mediastinal diameter, does not vary by gestational age (GA). We hypothesized that maternal AD and the use of anti-TNF agents affect fetal TT-ratio. STUDY DESIGN: This is a retrospective cohort study of ultrasound measurement of fetal thymus size in the mid-trimester. Patients included women with a singleton gestation who underwent fetal anatomical survey at a single ultrasound unit between 18 and 22 weeks of gestation and delivered between January 1, 2015 and December 31, 2017. The study group was comprised of women with AD. The control group was a cohort of healthy women. The primary outcome was fetal TT-ratio. Data on demographics, co-morbidities, and medication use was also collected. Groups were compared using X2 & T-Test as appropriate, with p< 0.05 as significance. RESULTS: 108 women with AD and 154 controls met inclusion criteria. The mean TT-ratio was smaller in women with AD than in healthy controls. (Table) In subgroup analysis, patients with AD without anti-TNF therapy demonstrated a smaller mean TT-ratio compared to healthy controls (0.41 v. 0.38 p¼0.007). There was no difference between mean TT-ratios of healthy controls and women on Anti-TNF therapy (0.41 v. 0.41, p¼1). CONCLUSION: The mean fetal TT-ratio was smaller in women with AD than in healthy controls, and more specifically in women not on anti-TNF agents versus healthy controls. Therefore, the use of anti-TNF therapy may protect against the effects of maternal AD on fetal thymus development. Further investigation of the interplay between the maternal and fetal immune response in the setting of AD and anti-TNF therapy is needed.