Diagnostic Yield of Serial PR Interval Screening for Fetal Heart Block in Anti-SSA/SSB Pregnancies

We conducted a retrospective cohort study of singleton pregnancies with anti-SSA and/or anti-SSB antibodies who underwent serial fetal echocardiography between 2010 and 2022. Surveillance was weekly from 18 to 28 weeks' gestation and monthly thereafter, with mechanical PR intervals obtained by pulsed Doppler. Prolonged PR interval was defined as ≥ 140 ms on three consecutive measurements.

A total of 124 pregnancies met the inclusion criteria. Screening began at a median of 19.5 week gestation and continued until 34 weeks, with a median of 14 ultrasounds and 10 PR interval measurements per pregnancy. Three fetuses (2.4%) were diagnosed with heart block: two with first-degree block and one with complete CHB, corresponding to one affected fetus per 359 screening ultrasounds. After dexamethasone, first-degree block either normalized or remained stable. Complete CHB did not reverse.

In a high risk, predominantly Hispanic and non-Hispanic black population, universal serial PR-interval screening detected conduction abnormalities at expected rates, but only two of three cases were identified early enough for potential intervention and detection required substantial screening burden per case. These findings support the reconsideration of universal screening and suggest that risk-targeted surveillance may better balance detection with screening burden.