Should continuous fetal heart‑rate monitoring be performed during penicillin desensitization for syphilis in a pregnant woman with a viable fetus (≥24 weeks gestation)?

Continuous Fetal Monitoring During Penicillin Desensitization for Syphilis in Pregnancy

Yes, continuous fetal heart-rate monitoring should be performed during penicillin desensitization for syphilis in pregnant women with viable fetuses (≥24 weeks gestation), and this monitoring should continue for at least 24 hours after the first dose of benzathine penicillin G. 1, 2

Rationale for Continuous Monitoring

The primary concern is the Jarisch-Herxheimer reaction, which occurs in approximately 40-44% of pregnant women treated for syphilis and can manifest with serious fetal consequences. 2, 3

Specific Fetal Risks During Treatment

• Regular uterine contractions develop in approximately 42% of treated pregnant women, with median onset at 10 hours post-injection. 3
• Recurrent variable decelerations occur in approximately 39% of cases, with median onset at 8 hours after treatment. 3
• Fetal distress and stillbirth are rare but documented complications, particularly in pregnancies with ultrasound evidence of fetal syphilis (hepatomegaly, hydrops). 4, 2
• Lower gestational ages are associated with higher rates of FHR abnormalities during the Jarisch-Herxheimer reaction. 3

Recommended Monitoring Protocol

All viable pregnancies (≥24 weeks gestation) should receive the first dose of benzathine penicillin G in a labor and delivery unit with continuous electronic fetal monitoring for at least 24 hours. 1, 2

Key Components of the Protocol

• Location: Administer the first penicillin dose in a labor and delivery department where immediate obstetric intervention is available. 2
• Duration: Continue monitoring for a minimum of 24 hours after injection, as most uterine contractions and FHR changes resolve within this timeframe. 3
• Subsequent doses: After the first monitored dose, remaining benzathine penicillin G injections (for late latent syphilis requiring three weekly doses) can be administered in an outpatient setting. 2

During Desensitization Itself

• Continuous fetal monitoring should be maintained throughout the entire desensitization procedure, as anaphylaxis can occur and may require intramuscular epinephrine. 5
• Case reports demonstrate that fetuses remain stable during maternal anaphylaxis treatment with intramuscular epinephrine, showing no decrease in variability, tachycardia, or decelerations. 5
• Desensitization should be performed in an obstetric emergency setting with adult and pediatric intensive care units immediately available. 6

Patient Counseling

Women must be instructed to seek immediate obstetric attention if they experience fever, uterine contractions, or decreased fetal movements within 24 hours of treatment. 1, 7

Important Reassurance Points

• The risk of stillbirth from the Jarisch-Herxheimer reaction is extremely rare and should never delay necessary treatment. 4, 1
• Untreated maternal syphilis poses far greater fetal harm than the treatment itself. 1, 8
• Most uterine contractions and FHR changes resolve spontaneously within 24 hours without requiring delivery. 3

High-Risk Pregnancies Requiring Enhanced Vigilance

Pregnancies with ultrasound abnormalities suggestive of fetal syphilis warrant obstetric specialist consultation and particularly close monitoring. 1, 2

Ultrasound Findings Indicating Higher Risk

• Fetal hepatomegaly 4, 2
• Placentomegaly 2
• Hydrops fetalis 4, 2
• Elevated peak systolic velocity in the middle cerebral artery (indicating fetal anemia) 2
• Ascites 2

These findings indicate greater risk for fetal compromise during treatment and potential treatment failure. 4, 2

Common Pitfalls to Avoid

• Do not perform desensitization or administer the first penicillin dose in an outpatient clinic without continuous fetal monitoring capability and immediate access to obstetric intervention. 2
• Do not delay treatment due to concerns about the Jarisch-Herxheimer reaction; the risk from untreated syphilis far exceeds treatment risks. 1, 8
• Do not assume subsequent doses require the same level of monitoring; only the first dose necessitates 24-hour inpatient monitoring. 2
• Do not use alternative antibiotics (erythromycin, tetracyclines, azithromycin, ceftriaxone) to avoid the monitoring requirement—these do not prevent congenital syphilis and penicillin desensitization is mandatory. 1, 7, 8