Penicillin desensitization is indicated in pregnant patients with severe allergies to penicillin with syphilis. The immediate effects of intramuscular epinephrine on the fetus during desensitization remain unreported. We describe a pregnant patient with secondary syphilis and penicillin allergy who developed anaphylaxis during penicillin desensitization. Anaphylaxis resolved after administration of intramuscular epinephrine. Throughout the procedure, continuous electronic fetal monitoring showed a stable fetus without a decrease in variability, tachycardia, decelerations, or signs of fetal distress. This case showed that intramuscular epinephrine is effective in treatment of anaphylaxis in a pregnant patient with little to no immediate effects on the fetus.