A42: Anti‐Ro and Anti‐La Antibodies in the General Pregnant Population: Rates and Fetal Outcomes

Abstract

Background/Purpose:Neonatal lupus erythematosus (NLE) is a passively transferred autoimmune disease that occurs in babies born to mothers with anti‐Ro and anti‐La antibodies. The most serious complication of NLE is congenital heart block (CHB). In pregnancies of mothers with a known autoimmune condition and positive anti‐Ro antibodies, the incidence of heart block is approximately 1‐2% of live births. We have previously shown that only mothers with moderate‐high titre antibodies are at risk to deliver a child with CHB. However, the rate of anti‐Ro positive antibody pregnant women in an otherwise healthy population is unknown or is their risk for delivering a child with CHB.Objectives: Determine the rate of anti‐Ro/La antibodies in the general pregnant population. Determine if the incidence of CHB is increased in healthy mothers with positive Ro/La antibodies compared to mothers with known autoimmune disease and positive anti‐Ro/La antibodies.Methods:Antibody testing was performed on 15198 pregnant women who were having concurrent Maternal Serum Screening in the Metropolitan Toronto area. Maternal self‐reported outcomes of prenatal, pregnancy, and post‐natal medical conditions were reported, along with fetal outcomes of pre and post‐natal illnesses. Autoantibody titres were stratified into negative, low, moderate, and high positive.Results:1152/151598 (7.6%) of the mothers who had anti‐Ro antibodies and 179/15198 (1.18%) had moderate‐high titres (at risk to deliver a child with CHB). 779 (5%) had anti‐La antibodies with the majority being low titre. During the course of the study there were 13 cases of CHB that were unrelated to our maternal sample population‐ 10 to well mothers and 3 to mothers with an autoimmune disease. All of these women mothers had moderate‐high titre anti‐Ro antibodies, while only 31% had moderate‐high titre anti‐La antibodies. During the course of the study 64 pregnant women with a known autoimmune disease and anti‐Ro antibodies (at risk to deliver a child with CHB) were prospectively followed. 3/64 delivered a child with CHB. All 3 of these mothers had moderate‐high titre anti‐Ro antibodies while 41/61 mothers who delivered a child without CHB had moderate‐high titre anti‐Ro antibodies. Therefore 3/44 (6.9%) mothers with moderate‐high titre anti‐Ro antibodies and an autoimmune disease delivered a child with CHB.Conclusion:The incidence of CHB is reported to be between 1:10/N15,000 pregnancies. Therefore, based on our data showing 1.18% of otherwise well pregnant woman had moderate‐high titre anti‐Ro antibodies (at risk to deliver a child with CHB), for each child with CHB we predict that 117—174 children without CHB will be delivered to otherwise healthy mothers. In contrast, in mothers with a known autoimmune disease and moderate‐high anti‐Ro antibody titre, we found a 6.9% incidence of CHB and therefore for each child with CHB there were 14 children without CHB born. Therefore the risk for a woman with a known autoimmune disease and moderate‐high titre anti‐Ro antibodies was approximately 10x that of otherwise healthy pregnant women. These data therefore suggest that the anti‐Ro antibody repertoire differs between these 2 groups of pregnant women.