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Objectives The objectives of this study were, first, to evaluate the association between fetal echocardiographic atrioventricular (AV) and magnetocardiographic (fMCG) PR intervals at different gestational ages (GAs) in normal and anti‐Ro/SSA‐antibody‐positive pregnancies; second, to determine if PR interval could be predicted by AV interval; and third, to assess the neonatal outcome of fetuses with prolonged AV and PR intervals, with the goal of developing criteria for fetal first‐degree AV block (AVB‐I). Methods This was a retrospective study of anti‐Ro/SSA‐antibody‐positive pregnancies (cases) and controls that underwent fMCG and fetal echocardiography at the same recording session. Cardiac cycle length, GA and AV (by mitral inflow/aortic outflow Doppler) and PR (by fMCG) intervals were measured. We tested for significant differences between AV and PR intervals using generalized estimating equations to account for repeat measurements, and assessed whether PR interval could be predicted reliably by AV interval. After delivery, infants with fetal AV or PR interval Z‐score ≥ 3 underwent 12‐lead electrocardiography. Results Thirty‐nine controls and 31 cases underwent 46 and 36 simultaneous fMCG and echocardiographic examinations, respectively; 101 controls and nine cases underwent fMCG only. AV and PR intervals increased with GA (P < 0.05 for both). Overall, AV and PR intervals were significantly different from each other (P < 0.001); this difference was not significant when compared between cases and controls (P = 0.222). PR interval could not be predicted accurately from AV interval and GA alone. Three of four cases with AV and PR interval Z‐scores > + 3 had postnatal AVB‐I despite treatment. The fourth fetus, which had predominately second‐degree AVB and rare periods of AVB‐I, progressed to third‐degree AVB despite treatment with dexamethasone. Conclusions The diagnostic threshold for AVB‐I, defined by AV interval Z‐score, is GA dependent. Based on the observed data, an AV interval Z‐score threshold of 3 (AV interval, 151–167 ms) may be appropriate. Echocardiographic AV interval was not predictive of fMCG‐PR interval. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Objectives:We compared simultaneous fetal echo AV intervals (E-AV) and magentocardiogram (fMCG) PR intervals (M-PR) in SSA+ and control pregnancies to determine if an AV interval of + 2 z-scores correlated with a prolonged M-PR interval and 1 • AV block. Methods: We searched the database of the University of Wisconsin Biomagnetism laboratory for pregnant women referred for fMCG with SSA antibodies. Maternal and pregnancy data were obtained from the mother's medical record. Fetal MCGs were performed using a 37-channel biomagnetometer (Magnes, 4D Neuroimaging, Inc). During the same session, we measured and averaged PR and cardiac RR intervals from 5 rhythm tracings and compared results to Echo Doppler AV interval (mitral inflow/aortic outflow) and RR intervals. Results were normalised for RR interval and compared by paired t-test. Regression analysis was used to test associations between gestational age (GA) and cardiac intervals. Results: The mean M-PR was 23.3 ms less than the mean E-AV (95% CI: 20.1,26.5, p<0.001); this statistically significant difference persisted when normalised for RR interval. There were no significant differences between SSA and controls for RR, PR, or AV intervals. Neither E-RR interval or GA were associated with predicting E-AV; nor were M-RR or GA associated with predicting M-PR. However, the interaction between E-AV interval and GA were significantly associated with the AV-PR difference of 23.3 ms. Conclusions: Our results suggests that E-AV overestimates M-PR in both SSA and controls. Using the previous definition of 1 • AVB (an AV interval of 150 ms) may result in unnecessary treatment of SSA+ normal fetuses. Objectives:To identify the prognostic factors present in prenatal and perinatal period that would be helpful in detecting the fetuses