Intrapartum Antibiotic Prophylaxis for Group B Streptococcus (GBS)

Standard Prophylaxis Regimen (Patients without Penicillin Allergy)

• Penicillin G 5 million units IV loading dose, then 2.5–3.0 million units IV every 4 hours until delivery; must be started ≥ 4 hours before birth to achieve optimal protection. 1
• Ampicillin 2 g IV loading dose, then 1 g IV every 4 hours until delivery; also requires administration ≥ 4 hours before delivery. 2

Low‑Risk Penicillin Allergy (No Anaphylaxis, Angioedema, Respiratory Distress, or Urticaria)

• Cefazolin 2 g IV loading dose, then 1 g IV every 8 hours until delivery; preferred because pharmacologic data show effective intra‑amniotic concentrations. 1

High‑Risk Penicillin Allergy (History of Anaphylaxis, Angioedema, Respiratory Distress, or Urticaria)

• Clindamycin 900 mg IV every 8 hours until delivery only when the GBS isolate is susceptible to both clindamycin and erythromycin. 1
• Clindamycin 900 mg IV every 8 hours may be used when the isolate is clindamycin‑susceptible but erythromycin‑resistant provided D‑zone testing for inducible clindamycin resistance is negative. 2
• Vancomycin 1 g IV every 12 hours until delivery is the alternative when inducible clindamycin resistance is present, when clindamycin susceptibility testing is not performed, or when the isolate is resistant to clindamycin. It is the default agent when susceptibility results are unavailable at labor onset. 3

Clindamycin Resistance Considerations

• Approximately 20 % of GBS isolates are resistant to clindamycin; therefore susceptibility testing is mandatory before clindamycin use, and the drug must never be given without documented susceptibility. 4

Timing Requirements for All Regimens

• All intrapartum antibiotics (penicillin G, ampicillin, cefazolin, clindamycin, vancomycin) must be administered at least 4 hours before delivery to achieve optimal effectiveness. 5

Neonatal Evaluation and Empiric Therapy

• Full diagnostic work‑up for neonates with signs of sepsis includes blood culture, CBC with differential, chest radiograph if respiratory signs are present, and lumbar puncture if the infant is stable. 1
• Empiric antimicrobial therapy for septic neonates: intravenous ampicillin plus an aminoglycoside (typically gentamicin) to cover GBS and gram‑negative organisms such as E. coli. 4
• Lumbar puncture importance: 15–38 % of infants with early‑onset meningitis have sterile blood cultures, making CSF analysis essential for optimal diagnostic sensitivity. 4
• Limited evaluation for well‑appearing neonates born to mothers with suspected chorioamnionitis: blood culture and CBC at birth and/or 6–12 hours of life. 2
• Empiric antibiotics are started pending culture results in these well‑appearing infants. 4

Indications for Intrapartum GBS Prophylaxis

• Positive GBS vaginal‑rectal culture within the preceding 5 weeks.
• GBS bacteriuria during the current pregnancy.
• Prior infant with GBS disease.
• Unknown GBS status plus any of the following risk factors: gestational age < 37 weeks, rupture of membranes ≥ 18 hours, or intrapartum temperature ≥ 38.0 °C.

Common Pitfalls to Avoid

• Do not use erythromycin for GBS prophylaxis because rising resistance renders it ineffective. 5
• Do not give cefazolin to patients with a history of urticaria, as this IgE‑mediated reaction carries a high risk of cross‑reactivity. 3
• Do not assume clindamycin susceptibility; resistance occurs in ~20 % of isolates and requires documented susceptibility before use. 4

Allergy Risk Stratification and Antibiotic Selection for Pregnant Patients with Penicillin Allergy

Allergy Risk Assessment

• In pregnant patients, the first step is to classify the penicillin/amoxicillin allergy as low‑risk (non‑IgE mediated) when the history consists of a mild rash, delayed‑onset rash, gastrointestinal upset, or a family history of allergy without a personal reaction. [​6]
• An allergy is considered high‑risk (IgE‑mediated) when the patient reports anaphylaxis, angioedema, respiratory distress, or urticaria that occurred immediately after penicillin or amoxicillin exposure. [​6]

Contraindications for High‑Risk (IgE‑Mediated) Allergy

• For patients identified as high‑risk, all beta‑lactam antibiotics—including all cephalosporins—should be avoided because of the increased risk of cross‑reactivity. [​6]
• Specifically, cephalosporins must not be used in patients who experienced urticaria, angioedema, anaphylaxis, or respiratory distress after penicillin/amoxicillin, as these IgE‑mediated reactions carry a higher cross‑reactivity risk. [​6]

Clinical Recommendation for Allergy History

• Clinicians should obtain a detailed allergy history in pregnant patients, explicitly asking about the timing of the reaction, the nature of symptoms (type of rash, respiratory involvement, swelling), and the severity of the event to accurately stratify risk. [​6]

All cited recommendations are derived from the Centers for Disease Control and Prevention (CDC) MMWR Recommendations and Reports (2010).​

Intrapartum Antibiotic Prophylaxis for GBS‑Positive Pregnant Women

Standard Regimen (No Penicillin Allergy)

• Penicillin G 5 million units IV loading dose, then 2.5–3 million units IV every 4 hours until delivery; administration should begin at least 4 hours before birth to ensure optimal fetal protection. 7, 8
• The 2.5–3 million‑unit maintenance range provides adequate fetal and amniotic fluid concentrations while minimizing neurotoxicity risk; the exact dose is chosen based on available pharmacy formulations. 7, 8

High‑Risk Penicillin‑Allergic Patients (Anaphylaxis, Angioedema, Respiratory Distress, or Urticaria)

When GBS Is Susceptible to Both Clindamycin and Erythromycin

• Clindamycin 900 mg IV every 8 hours until delivery is the recommended regimen. 9, 8

When GBS Is Clindamycin‑Susceptible but Erythromycin‑Resistant

• Clindamycin 900 mg IV every 8 hours may be used only after a negative D‑zone test confirming the absence of inducible clindamycin resistance. 9, 8

When GBS Is Clindamycin‑Resistant or Susceptibility Is Unknown

• Vancomycin 1 g IV every 12 hours until delivery is the default therapy. 9, 8

Critical Timing Requirement

• All intrapartum antibiotics must be administered ≥ 4 hours before delivery to achieve optimal prophylactic effectiveness. 7, 8
• Obstetric procedures that are medically necessary should not be delayed solely to reach a 4‑hour antibiotic exposure window. 9, 7, 8

Antibiotics to Avoid

• Erythromycin is no longer acceptable for GBS prophylaxis because of increasing macrolide resistance among GBS isolates. 9, 7, 8, 10

Laboratory and Susceptibility Testing

• GBS antimicrobial susceptibility testing is mandatory before clindamycin is used for prophylaxis in penicillin‑allergic patients. 9
• Clinicians should inform microbiology laboratories to perform susceptibility testing whenever a penicillin allergy is documented. 9