Abstract

Objective Approximately 2.8% of pregnancies are Ro /La antibody positive. Three to 15% fetuses develop complete heart block (CHB). First degree atrioventricular heart block (10 AVB) is reported in a third of Ro/La fetuses but as most have normal postnatal ECG may reflect inadequacies of Doppler measurement techniques.

Design We compared mechanical (mPR) and electrical (ePR) intervals obtained prospectively using Doppler and non-invasive fetal ECG (fECG) in 52 consecutive Ro/La pregnancies in 46 women carrying 54 fetuses in an observational study.

Setting Fetal Medicine Unit

Methods & results We recorded 121 mPR and 37 ePR intervals in 49 Ro/La fetuses. Five were referred with CHB and excluded. ePR was measured successfully in 35/ 37 (94%) and mPR in all. 10 AVB was defined as PR > 95% CI. Logistic regression predicted abnormal final fetal rhythm from first mPR or ePR. ePR model gave 66.7% sensitivity (6 of 8 final abnormal fetal rhythm cases predicted correctly in fetuses >20 weeks) and 96.2% specificity and mPR 44.4% sensitivity (4 of 9 cases) and 88.5% specificity. Z scores for ePR (zPR) were calculated from 199 normal fetuses. Area under ROC curve was 0.88 (95% CI 0.754,1.007). A cut-off of 1.65 gave sensitivity of 87.5% and specificity of 95% for those with prolonged and normal ePR intervals respectively.

Conclusions zPR is better than mPR in differentiating between normal and prolonged PR interval suggesting fECG is the diagnostic tool of choice to investigate the natural history and therapy of conduction abnormalities in Ro/La pregnancies.