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Obstetrics & Gynecology: November 1998
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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 χ2 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.

Address reprint requests to: Thomas D. Myles, MD, Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, University of Illinois at Chicago, 820 South Wood Street (M/C 808), Chicago, IL 60612. E-mail:

© 1998 The American College of Obstetricians and Gynecologists

The treatment of syphilis with penicillin after 24 weeks&apos; gestation can result in the Jarisch-Herxheimer reaction, uterine contractions, or variable decelerations in a substantial proportion of cases.