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

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. [ABSTRACT FROM AUTHOR]