Why do you get gbs in pregnancy

Overview

Group B Streptococcus (GBS), scientifically known as Streptococcus agalactiae, is a gram-positive bacterium that colonizes the gastrointestinal and genital tracts of approximately 10-30% of pregnant women worldwide. First identified as a significant perinatal pathogen in the 1970s, GBS emerged as the leading cause of neonatal sepsis and meningitis in developed countries before prevention protocols were established. The bacterium typically causes no symptoms in healthy adults but can be transmitted vertically from mother to baby during labor and delivery. Historical data shows that before routine screening and antibiotic prophylaxis, GBS caused approximately 7,500 cases of neonatal disease annually in the United States alone, with mortality rates reaching 50% for early-onset infections in the 1970s. The development of prevention guidelines in the 1990s, particularly after landmark studies published in 1996, transformed neonatal outcomes dramatically.

How It Works

GBS colonization occurs when the bacterium establishes itself in the maternal gastrointestinal tract, then migrates to the vaginal and rectal areas. During pregnancy, hormonal changes and immune system adaptations can alter the vaginal microbiome, potentially increasing GBS colonization rates. Transmission to the newborn happens primarily during passage through the birth canal when the baby comes into contact with GBS-containing secretions. The bacteria can ascend into the amniotic fluid or infect the baby during delivery. Once in the newborn, GBS can cause two types of disease: early-onset (occurring within the first week of life, usually within 24-48 hours) and late-onset (occurring between 1 week and 3 months). The pathogenesis involves bacterial invasion through mucosal surfaces, followed by bloodstream dissemination that can lead to sepsis, pneumonia, or meningitis. Risk factors for transmission include prolonged rupture of membranes (>18 hours), maternal fever during labor, preterm delivery (<37 weeks), and previous infant with GBS disease.

Why It Matters

GBS prevention represents one of the most successful public health interventions in perinatal medicine. Since implementation of universal screening and intrapartum antibiotic prophylaxis, early-onset GBS disease incidence has decreased by approximately 80% in the United States, from 1.7 cases per 1,000 live births in the 1990s to about 0.23 cases per 1,000 live births today. This translates to thousands of prevented neonatal deaths and disabilities annually. However, GBS remains a significant concern globally, particularly in resource-limited settings where screening and antibiotic access may be limited. Ongoing research focuses on vaccine development, with several candidates in clinical trials that could potentially eliminate the need for intrapartum antibiotics. The economic impact is substantial too - each case of neonatal GBS disease costs approximately $30,000-$50,000 in medical care, making prevention both clinically and economically vital.