What can cause a complete or third-degree heart block in a fetus?

Complete or third-degree heart block in a fetus is most commonly associated with maternal conditions, particularly autoimmune disorders like systemic lupus erythematosus (SLE). In cases where maternal lupus is present, the antibodies produced by the mother, particularly anti-Ro (SS-A) and anti-La (SS-B), can cross the placenta and affect the fetal conduction system. This can lead to congenital heart block, which manifests as a complete or third-degree heart block.

Maternal diabetes, hypertension, and obesity can have various impacts on fetal development and can contribute to other complications during pregnancy, but they are not typically linked to the specific risk of congenital heart block in the same way that maternal lupus is. The relationship between maternal autoimmune conditions and fetal heart block is well-established and highlights the importance of monitoring and managing maternal health conditions to mitigate their potential impact on fetal development.