We evaluated the efficacy of dexamethasone (DEX) in anti-SSA/Ro-exposed fetuses newly diagnosed with congenital heart block. Previous use of DEX has been anecdotal with varying reports of therapeutic benefit. This was a multicenter, open-label, nonrandomized study involving 30 pregnancies treated with DEX (22 with third-degree block, 6 with second-degree block, 2 with first-degree block) and 10 untreated (9 with third-degree block, 1 with first-degree block). Initial median ventricular rates, age at diagnosis, and degree of cardiac dysfunction were similar between groups. Six deaths occurred in the DEX group. There was no reversal of third-degree block with therapy or spontaneously. In fetuses treated with DEX, 1/6 with second-degree block progressed to third-degree block and 3 remained in second-degree block (postnatally 1 paced, 2 progressed to third degree); 2 reverted to normal sinus rhythm (NSR; postnatally 1 progressed to second degree). DEX reversed the 2 fetuses with first-degree block to NSR by 7 days with no regression at discontinuation. Absent DEX, the 1 with first-degree block detected at 38 weeks had NSR at birth (overall stability or improvement in 4 of 8 in the DEX group vs 1 of 1 in the non-DEX group). Median gestational birth age was 37 weeks in the DEX group versus 38 weeks in the non-DEX group (p = 0.019). Prematurity and small size for gestational age were restricted to the DEX group. Pacemaker use and growth parameters at birth and 1 year were similar between groups. In conclusion, these data confirm the irreversibility of third-degree block and progression of second- to third-degree block despite DEX. A potential benefit of DEX in reversing first- or second-degree block was supported in rare cases but should be weighed against potential steroid side effects such as growth restriction.