The American College of Obstetricians and Gynecologists, the American Academy of Pediatrics, and the Centers for Disease Control and Prevention (CDC) published guidelines in 1996 recommending a risk-based (screening) approach, to determine when to recommend intravenous (IV) antibiotic prophylaxis during labor. It was determined that women with the following risk factors should be offered (IV) antibiotics during labor and delivery, not before labor:
• fever during labor
• rupture of membranes 18 hours or more before delivery
• labor or rupture of membranes before 37 weeks
As of 2002, the CDC revised the 1996 guidelines, recommending routine screening for all pregnant women between 35 and 37 weeks gestation, and universal treatment for women who test positive for group B Streptococcus during pregnancy (Box CDC 2002 group B Streptococcus Treatment Guidelines).
CDC 2002 group B Streptococcus Treatment Guidelines
• All pregnant women should be screened at 35 to 37 week gestation for vaginal and rectal group B Streptococcus colonization. At the time of labor or rupture of membranes, intrapartum chemoprophylaxis should be given to all pregnant women identified as group B Streptococcus carriers. Colonization during a previous pregnancy is not an indication for intrapartum prophylaxis in subsequent deliveries. Screening to detect group B Streptococcus colonization in each pregnancy will determine the need for prophylaxis in that pregnancy.
• Women with group B Streptococcus isolated from the urine in any concentration during their current pregnancy should receive intrapartum chemoprophylaxis because such women usually are heavily colonized with group B Streptococcus and are at increased risk of delivering an infant with early-onset group B Streptococcus disease. Prenatal culture-based screening at 35 to 37 week gestation is not necessary for women with group B Streptococcus bacteriuria. Women with symptomatic or asymptomatic group B Streptococcus urinary tract infection detected during pregnancy should be treated according to current standards of care for urinary tract infection during pregnancy.
• Women who have previously given birth to an infant with invasive group B Streptococcus disease should receive intrapartum chemoprophylaxis; prenatal culture-based screening is not necessary for these women.
• If the result of group B Streptococcus culture is not known at the onset of labor, intrapartum chemoprophylaxis should be administered to women with any of the following risk factors: gestation <37 weeks, duration of membrane rupture >18 hours, or a temperature of >100.4° F (>38.0° C). Women with known negative results from vaginal and rectal group B Streptococcus screening cultures within 5 weeks of delivery do not require prophylaxis to prevent group B Streptococcus disease even if any of the intrapartum risk factors develop.
• Women with threatened preterm (<37 week gestation) delivery should be assessed for need for intrapartum prophylaxis to prevent perinatal group B Streptococcus disease.
• In the absence of group B Streptococcus urinary tract infection, antimicrobial agents should not be used before the intrapartum period to treat group B Streptococcus colonization. Such treatment is not effective in eliminating carriage or preventing neonatal disease and may cause adverse consequences.
• Group B Streptococcus-colonized women who have a planned cesarean delivery performed before rupture of membranes and onset of labor are at low risk for having an infant with early-onset group B Streptococcus disease. These women should not routinely receive intrapartum chemoprophylaxis for perinatal group B Streptococcus disease prevention.
• For intrapartum chemoprophylaxis, the following regimen is recommended for women without penicillin allergy: penicillin G, 5 million units intravenously initial dose, then 2.5 million units intravenously every 4 hours until delivery. Because of its narrow spectrum of activity, penicillin is the preferred agent. An alternative regimen is ampicillin; 2 g intravenously initial dose, then 1 g intravenously every 4 hours until delivery (Al).
• Intrapartum chemoprophylaxis for penicillin-allergic women takes into account increasing resistance to clindamycin and erythromycin among group B Streptococcus isolates. During prenatal care, history of penicillin allergy should be assessed to determine whether a patient is at high risk for anaphylaxis, that is, has a history of immediate hypersensitivity reactions to penicillin (e.g., anaphylaxis, angioedema, or urticaria) or history of asthma or other conditions that would make anaphylaxis more dangerous. Women who are not at high risk for anaphylaxis should be given cefazolin; 2 g intravenously initial dose, then 1 g intravenously every 8 hours until delivery. For women at high risk for anaphylaxis, clindamycin and erythromycin susceptibility testing, if available, should be performed on isolates obtained during group B Streptococcus prenatal carriage screening. Women with clindamycin- and erythromycin-susceptible isolates should be given either clindamycin, 900 mg intravenously every 8 hours until delivery; OR erythromycin, 500 mg intravenously every 6 hours until delivery. If susceptibility testing is not possible, susceptibility results are not known, or isolates are resistant to erythromycin or clindamycin, the following regimen can be used for women with immediate penicillin hypersensitivity: vancomycin, 1 g intravenously every 12 hours until delivery.
• Routine use of antimicrobial prophylaxis for newborns whose mothers received intrapartum chemoprophylaxis for group B Streptococcus infection is not recommended. However, therapeutic use of these agents is appropriate for infants with clinically suspected sepsis.
Women with negative vaginal and rectal group B Streptococcus screening cultures within 5 weeks of delivery do not require intra-partum antimicrobial prophylaxis for group B Streptococcus even if obstetric risk factors develop (i.e., delivery at <37 weeks’ gestation, duration of membrane rupture >18 hours, or temperature >100.4° F [>38.0° C]).
The use of prophylactic perinatal intravenous antibiotics is attributed with a 70% reduction in the incidence of group B Streptococcus disease during the last 10 years. In spite of this reduction in incidence, early-onset group B Streptococcus-related diseases such as pneumonia and meningitis remain a cause of illness and death in newborns in the United States, with a rate of approximately 80 deaths annually.
An alternative conventional treatment to intravenous antibiotic prophylaxis that has been investigated in Europe but is not employed in the United States other than by mid-wives, is the use of chlorhexidine vaginal flushings. A randomized controlled study was conducted to investigate the efficacy of intrapartum vaginal flushings with chlorhexidine compared with ampicillin in preventing group B streptococcus transmission to neonates. The study evaluated outcomes of singleton pregnancies delivering vaginally. Rupture of membranes, when present, must not have occurred more than 6 hours prior. Women with any gestational complication, with a newborn previously affected by group B streptococcus sepsis or whose cervical dilatation was greater than 5 cm were excluded. A total of 244 group B streptococcus-colonized mothers at term (screened at 36 to 38 weeks) were randomized to receive either 140 mL chlorhexidine 0.2% by vaginal flushings every 6 hours or ampicillin 2 g intravenously every 6 hours until delivery. Neonatal swabs were taken at birth, at three different sites (nose, ear, and gastric juice). A total of 108 women were treated with ampicillin and 109 with chlorhexidine. Their ages and ges-tational weeks at delivery were similar in the two groups. Nulliparous women were equally distributed between the two groups (ampicillin, 87%; chlorhexidine, 89%). Clinical data such as birth weight (ampicillin, 3,365 ± 390 g; chlorhexidine, 3,440 ± 452 g), Apgar scores at 1 minute (ampicillin, 8.4 ± 0.9; chlorhexidine, 8.2 ± 1.4), and at 5 min (ampicillin, 9.7 ± 0.6; chlorhexidine, 9.6 ± 1.1) were similar for the two groups, as was the rate of neonatal group B streptococcus colonization (chlorhexidine, 15.6%; ampicillin, 12%). Escherichia coli, on the other hand, was significantly more prevalent in the ampicillin (7.4%) than in the chlorhexidine group (1.8%, p < 0.05). Six neonates were transferred to the neonatal intensive care unit, including two cases of early-onset sepsis (one in each group). In this carefully screened target population, intrapartum vaginal flushings with chlorhexidine in colonized mothers displayed the same efficacy as ampicillin in preventing vertical transmission of group B streptococcus. Moreover, the rate of neonatal E. coli colonization was reduced by chlorhexidine. Additional studies have demonstrated the efficacy of this practice, but for unknown reasons it has not been more widely investigated or employed in the United States.S This is an option that many midwives in the United States are beginning to employ in home birth settings; clearly more investigation of this option should be conducted to determine whether it is a safe and effective alternative to routine intranatal intravenous prophylaxis for neonatal group B Streptococcus infection. Until then, intravenous antibiotic prophylaxis remains the recommended standard.