How should a pregnant woman with a positive group B Streptococcus screen be managed with intrapartum antibiotic prophylaxis, and what ocular prophylaxis should be given to the newborn?

Management of Maternal GBS Colonization and Newborn Eye Prophylaxis

Maternal GBS Management

All pregnant women should undergo vaginal-rectal GBS screening at 35-37 weeks' gestation, and those who test positive must receive intravenous penicillin G or ampicillin during labor, administered at least 4 hours before delivery to achieve 78% reduction in early-onset neonatal GBS disease. 1

Universal Screening Protocol

• Collect vaginal and rectal specimens at 36 0/7 to 37 6/7 weeks' gestation using a single swab (or two separate swabs): first swab the lower vagina (vaginal introitus), then insert the same swab through the anal sphincter into the rectum. 2

• Specimens should be placed in selective broth medium with overnight incubation, then subcultured onto blood agar to maximize GBS detection. 2

• Women with GBS bacteriuria at any concentration during any trimester automatically qualify for intrapartum prophylaxis, regardless of whether the UTI was treated earlier in pregnancy. 3, 2

• Women with a previous infant who had invasive GBS disease automatically require intrapartum prophylaxis without screening. 2

Intrapartum Antibiotic Prophylaxis Regimens

For women without penicillin allergy:

• First-line: Penicillin G 5 million units IV initially, then 2.5-3.0 million units IV every 4 hours until delivery. 1, 4

• Alternative: Ampicillin 2 g IV initially, then 1 g IV every 4 hours until delivery. 1, 4

For women with penicillin allergy (not high-risk for anaphylaxis):

• Preferred: Cefazolin 2 g IV initially, then 1 g IV every 8 hours until delivery. 1, 4

For women with high-risk penicillin allergy (history of anaphylaxis, angioedema, respiratory distress, or urticaria):

• If GBS isolate is susceptible to clindamycin and erythromycin: Clindamycin 900 mg IV every 8 hours until delivery. 1, 4

• If susceptibility unknown or resistant: Vancomycin 1 g IV every 12 hours until delivery. 1, 4

Critical Timing Requirements

• Prophylaxis must be administered at least 4 hours before delivery for optimal effectiveness—this achieves 78% reduction in early-onset neonatal GBS disease. 1

• Even if a woman received only 1-2 doses or less than 4 hours of antibiotics, some protective effect occurs, but this is considered "inadequate" prophylaxis. 5, 6

Special Clinical Scenarios

Preterm labor (<37 weeks):

• Screen for GBS at hospital admission unless screening was performed within the preceding 5 weeks. 1, 2

• Start GBS prophylaxis immediately at admission if GBS status is positive or unknown. 1, 3

• Discontinue prophylaxis if patient is not in true labor. 1, 2

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 both latency prolongation and adequate GBS prophylaxis. 3

Cesarean delivery before labor with intact membranes:

• Intrapartum GBS prophylaxis is not routinely recommended, regardless of GBS status or gestational age. 1

• However, women should still undergo routine screening at 35-37 weeks because labor or membrane rupture can occur before the planned cesarean. 1

Common Pitfalls to Avoid

• Never treat asymptomatic GBS colonization with oral or IV antibiotics before labor—this is completely ineffective at eliminating carriage, promotes antibiotic resistance, and does not prevent neonatal disease. 1, 4, 2

• Do not assume that treating a GBS UTI earlier in pregnancy eliminates the need for intrapartum prophylaxis—recolonization after oral antibiotics is typical, and IV prophylaxis during labor remains mandatory. 3

• For penicillin-allergic patients at high risk for anaphylaxis, susceptibility testing for clindamycin and erythromycin must be performed on the prenatal GBS isolate, as clindamycin resistance ranges from 3-15%. 4, 7

• Verify penicillin allergy history carefully—many reported penicillin allergies are not true IgE-mediated reactions, and patients may be candidates for penicillin or cefazolin rather than alternatives. 4

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Newborn Eye Prophylaxis with Erythromycin

Newborn eye prophylaxis with erythromycin ophthalmic ointment is a separate intervention from GBS prophylaxis and is administered to prevent gonococcal and chlamydial ophthalmia neonatorum, not GBS disease. This is standard practice based on general medical knowledge, though the provided evidence does not specifically address erythromycin eye prophylaxis.

Key Distinction

• Erythromycin eye ointment does NOT prevent or treat neonatal GBS disease—it targets Neisseria gonorrhoeae and Chlamydia trachomatis eye infections.

• Maternal intrapartum IV antibiotics (penicillin G or ampicillin) are what prevent early-onset neonatal GBS disease, not topical eye prophylaxis.

Standard Newborn Eye Prophylaxis Protocol

• Erythromycin 0.5% ophthalmic ointment is applied to both eyes within 1 hour of birth as universal prophylaxis against gonococcal and chlamydial conjunctivitis.

• This intervention is required by law in most jurisdictions and is administered to all newborns regardless of maternal GBS status or intrapartum antibiotic administration.