What is the treatment for a pregnant woman with a positive Group B (Streptococcus) vaginal swab?

Treatment for Positive Group B Streptococcal Vaginal Swab in Pregnancy

A positive GBS vaginal swab in pregnancy does NOT require treatment at the time of detection—treatment is reserved exclusively for intrapartum antibiotic prophylaxis during active labor to prevent early-onset neonatal GBS disease. 1

Critical Understanding: When NOT to Treat

• Do not administer antibiotics before labor begins, as prenatal treatment is ineffective at eliminating GBS colonization and may cause antibiotic resistance and adverse drug effects without providing any benefit to the mother or baby 1, 2
• GBS vaginal colonization outside of labor is a normal finding in 10-15% of pregnant women and represents asymptomatic carriage that should be left untreated until labor onset 3
• The only exception requiring immediate treatment is GBS bacteriuria (GBS in urine) at any concentration, which indicates heavy colonization and requires both immediate UTI treatment and subsequent intrapartum prophylaxis during labor 1

When Treatment IS Indicated: Intrapartum Prophylaxis During Labor

Intrapartum antibiotic prophylaxis should be administered during active labor for women who meet any of the following criteria:

• Positive GBS screening culture at 35-37 weeks gestation 4
• GBS bacteriuria at any concentration detected at any point during the current pregnancy (even if previously treated) 1
• Previous infant with invasive GBS disease 2
• Unknown GBS status with risk factors: delivery <37 weeks, membrane rupture ≥18 hours, or intrapartum temperature ≥100.4°F 2

Recommended Antibiotic Regimens for Intrapartum Prophylaxis

First-Line Treatment (No Penicillin Allergy)

• Penicillin G: 5 million units IV initially, then 2.5 million units IV every 4 hours until delivery (preferred agent due to narrow spectrum and high efficacy) 1
• Ampicillin: 2 g IV initially, then 1 g IV every 4 hours until delivery (acceptable alternative with broader spectrum) 1

Penicillin-Allergic Patients (Not High Risk for Anaphylaxis)

• Cefazolin: 2 g IV initially, then 1 g IV every 8 hours until delivery (preferred alternative for non-anaphylactic allergy) 1, 5

Penicillin-Allergic Patients (High Risk for Anaphylaxis)

High-risk features include history of anaphylaxis, angioedema, urticaria, or asthma that would make anaphylaxis more dangerous 5

• Clindamycin: 900 mg IV every 8 hours (only if GBS isolate confirmed susceptible on testing) 1, 5
• Vancomycin: 1 g IV every 12 hours (if susceptibility testing unavailable or isolate resistant to clindamycin) 1, 5
• Susceptibility testing for clindamycin and erythromycin is mandatory for penicillin-allergic women at high risk for anaphylaxis 1, 5

Special Clinical Scenarios

Preterm Labor (<37 Weeks)

• Women admitted with signs of preterm labor should receive immediate GBS prophylaxis at hospital admission if GBS status is unknown or positive within the preceding 5 weeks 4
• If patient enters true labor, continue prophylaxis until delivery 4
• If not in true labor, discontinue prophylaxis and obtain culture results 4
• If GBS-positive and preterm labor resolves, repeat screening at 35-37 weeks if still undelivered 4

Preterm Premature Rupture of Membranes (PPROM)

• Ampicillin 2 g IV once, followed by 1 g IV every 6 hours for at least 48 hours provides adequate coverage for both latency and GBS prophylaxis 4
• If patient enters labor, continue antibiotics until delivery 4
• If not in labor after 48 hours, discontinue GBS prophylaxis (continue latency antibiotics per standard care if indicated) 4

Planned Cesarean Delivery

• No GBS prophylaxis is needed for women undergoing planned cesarean delivery before labor onset and before membrane rupture, regardless of GBS status 1, 2

Timing and Efficacy

• Administer prophylaxis ≥4 hours before delivery for maximum effectiveness—this reduces early-onset neonatal GBS disease by 78% 1
• Prophylaxis given <4 hours before delivery is less effective but still recommended 6, 7
• A negative GBS screen remains valid for 5 weeks; rescreening is required if >5 weeks have elapsed 4

Critical Pitfalls to Avoid

• Never treat asymptomatic GBS vaginal colonization outside of labor—this is the most common error and provides no benefit while promoting resistance 1, 2
• Do not rely on GBS screening from previous pregnancies; each pregnancy requires new screening at 35-37 weeks 2
• Do not skip intrapartum prophylaxis in women with GBS bacteriuria during pregnancy, even if the UTI was treated months earlier—recolonization is typical 1
• Ensure adequate timing: women spending >60 minutes in hospital before delivery should receive prophylaxis, as many "inadequate" prophylaxis cases result from delayed administration 7
• For women with suspected amnionitis, use broad-spectrum antibiotics that include GBS coverage rather than GBS prophylaxis alone 2