The Jarisch-Herxheimer reaction and fetal monitoring changes in pregnant women treated for syphilis

Obstet Gynecol. 1998 Nov;92(5):859-64. doi: 10.1016/s0029-7844(98)00271-3.


Objective: To estimate the incidence of the Jarisch-Herxheimer reaction in pregnant women undergoing treatment of syphilis and the incidence of changes in uterine activity or fetal heart rate (FHR).

Methods: Pregnant women of at least 24 weeks' gestation diagnosed as needing treatment of syphilis were reviewed retrospectively. Patients were admitted for their first dose of benzathine penicillin, and the FHR was recorded continuously before and for 24 hours after injection. The occurrence of the Jarisch-Herxheimer reaction was noted, and all available FHR records for this admission were reviewed. Evaluations for changes in the FHR pattern and uterine activity were made. Statistical comparisons used Student t, Fischer exact, and chi2 tests, when applicable (significance P < .05).

Results: We reviewed 50 charts and 31 available FHR records. The average gestational age was 30.8 weeks. We found 20 cases of probable Jarisch-Herxheimer reaction (40%). Thirteen of 31 patients (41.9%) developed regular uterine contractions, median onset, 10 hours. All resolved within 24 hours of treatment. Patients with uterine contractions had a greater mean increase in temperature (1.15F versus 0.68F, P < .008). Twelve of 31 women (38.7%) developed recurrent variable decelerations, median onset, 8 hours. All patients but one had their contractions resolve within 24 hours of treatment. Lower gestational age was associated with the occurrence of recurrent variable decelerations (29.6 weeks versus 32.3 weeks, P < .05). No patients required delivery at the time of treatment.

Conclusion: The incidence of Jarisch-Herxheimer reaction in treated syphilitic pregnancies is about 40%; similar proportions of patients develop regular uterine contractions and recurrent variable decelerations.

MeSH terms

  • Adult
  • Female
  • Fetal Monitoring
  • Fever / etiology*
  • Heart Rate, Fetal / physiology*
  • Humans
  • Penicillin G Benzathine / therapeutic use
  • Penicillins / therapeutic use
  • Pregnancy
  • Pregnancy Complications, Infectious / drug therapy*
  • Pregnancy Complications, Infectious / physiopathology
  • Retrospective Studies
  • Statistics as Topic
  • Syphilis / drug therapy*
  • Syphilis / physiopathology
  • Uterine Contraction / physiology*


  • Penicillins
  • Penicillin G Benzathine