GBS is a bacteria that lives in the genital tract of 1 in 4 American adults & is mostly harmless, but has a small chance of causing severe illness to a baby born to a GBS positive mother.

The US recommends universal screening which means screening all mothers for GBS. However, many countries including ones with some of the best maternal & neonatal outcomes, have chosen to screen only women with known risk factors. This is called risk-based screening.

Evidence shows a full-term healthy baby has a less than 1% chance of contracting invasive GBS disease if the mother is positive. When retrospectively looking at those who did contract GBS disease (the less than 1%), we see 2.7% will result in a fatality.

When pooling multiple sources of evidence, The Birth Review estimates that the chance of death for a full-term healthy baby born to a positive mother (not treated prophylactically) is 0.0203% OR approximately 1 in 4,938 babies.

Risk of infection or severe invasive disease increases with certain risk factors, the primary one being an earlier gestational age. Prolonged rupture of membranes, maternal fever and a previous baby affected by GBS disease are some of the other additional risk factors.

GBS disease is transient meaning it comes and goes which poses concern for accuracy when testing mothers prenatally. Evidence shows anywhere from 61.4% to 82% of babies who developed GBS disease were from mothers who actually tested negative.

Evidence on rapid test show around a 90% accuracy in detection and a 4% false positive detection. This accuracy is greater than the evidence we see with prenatal testing accuracy, however ACOG does not recommend replacing prenatal testing with rapid test.

Group B Strep “GBS”
GBS is a type of bacteria that commonly lives in the intestines and genital tract, including the vagina, usually without causing symptoms. It can pass from mother to baby during birth and sometimes cause serious infections in newborns (CDC, 2025A).

Colonization
The presence of Group B Streptococcus (GBS) bacteria in the body, typically in the digestive or reproductive tract, without causing illness or symptoms. Colonization is not the same as having a GBS infection (CDC, 2025A).

GBS Disease or Invasive GBS
GBS disease refers to an infection caused by Group B Streptococcus bacteria. Invasive GBS is a more specific term used when the bacteria are detected in a normally sterile area of the body, such as the blood or fluid surrounding the brain and spinal cord. In newborns, serious GBS infections can include sepsis, pneumonia, and meningitis (CDC, 2025A; CDC, 2024).

Intact Membranes
When the amniotic sac surrounding the baby has not broken and the amniotic fluid remains contained within the sac. This is commonly described as the mother's water not having broken (ACOG, N.D.).

Sepsis
A life-threatening medical emergency that occurs when the body's response to an infection causes widespread harm and can lead to organ damage or failure (CDC, 2026A). GBS is one of the bacteria that can cause sepsis in newborns (CDC, 2026B).

Pneumonia
An infection of the lungs that can cause inflammation and difficulty breathing. In newborns, pneumonia may be caused by GBS bacteria and can be a serious complication of GBS disease (CDC, 2025A).

Meningitis
An infection and inflammation of the protective membranes surrounding the brain and spinal cord. GBS meningitis is a serious infection in newborns that can sometimes lead to long-term neurological complications (CDC, 2025A).

Universal GBS Screening
The routine testing of pregnant women for Group B Streptococcus, regardless of symptoms or known risk factors. In the United States, screening is generally performed using a vaginal and rectal swab between 36 weeks, 0 days and 37 weeks, 6 days of pregnancy, with certain exceptions (ACOG, 2020).

Community-Based or Traditional Midwife
A community-based midwife provides maternity care within the community, often outside a hospital setting, and may have formal education, certification, or licensure. A traditional midwife or birth attendant typically acquires childbirth knowledge through experience, cultural practices, or apprenticeship rather than formal professional education. These terms are not interchangeable, and training and qualifications vary between countries (ICM, 2024; WHO, 2012).

Early-Onset GBS
GBS disease that develops in a newborn during the first six days of life (birth through day 6). It most commonly develops within the first 24–48 hours after birth and is generally associated with exposure to GBS bacteria before or during delivery (CDC, 2025A).

Late-Onset GBS
GBS disease that develops in an infant between 7 and 89 days of age. Unlike early-onset disease, late-onset GBS may result from exposure during birth or from other sources after delivery (CDC, 2025A).

Intrapartum
The period during labor and childbirth. In GBS prevention, intrapartum antibiotics refers to antibiotics administered to the mother during labor to reduce the risk of early-onset GBS disease in the newborn (ACOG, 2020).

NICU
An abbreviation for Neonatal Intensive Care Unit, a specialized hospital unit providing advanced medical care and monitoring for newborns who are premature, critically ill, or experiencing complications. Babies with serious GBS infections may require NICU care (NLM, 2024).

CBC
An abbreviation for Complete Blood Count, a blood test that measures components of the blood, including red blood cells, white blood cells, and platelets. In newborns with suspected GBS infection, a CBC may help assess signs of infection but cannot independently confirm GBS disease (NLM, 2024).

Intra-amniotic Infection/Chorioamnio
An infection involving the amniotic fluid, placenta, fetal membranes, or surrounding tissues during pregnancy or labor. It can be associated with maternal fever and an increased risk of infection in the newborn, including GBS-related infection (ACOG, 2017).

Labor Augmentation
Medical interventions used to strengthen or increase the frequency of contractions after labor has already begun. Common methods include administering synthetic oxytocin (Pitocin) or artificially breaking the amniotic sac (AROM) to encourage labor progression (WHO, 2014).

Streptococcus agalactiae, commonly known as Group B Streptococcus (GBS), is a bacterium often carried in the human gut or vagina (WHO, 2026).

When GBS is present in the gastrointestinal or genital tract without causing symptoms or infection, it is called colonization or carriage—not GBS disease. The CDC explains that most of the time GBS bacteria “aren’t harmful and don’t make people feel sick” (CDC, 2025).

GBS usually remains colonization of the lower gastrointestinal and vaginal tract. It can ascend into the uterus even with intact membranes, but rupture of membranes—and especially longer duration after rupture—makes ascending infection more likely (AAP, 2019; BROKAW ET AL., 2021).

GBS colonization can change over time. The bacteria may come and go, meaning a person can test positive at one point and negative at another. Colonization may be temporary, intermittent, or persistent (ACOG,2020; CDC, 2025).

(RUSSELL ET AL., 2017; ACOG, 2020)

The greatest concern with GBS is not colonization or exposure alone, but the small chance that an infant born vaginally will develop serious GBS disease (or invasive GBS)—most commonly bloodstream infection or sepsis, pneumonia, or meningitis—which can be life-threatening and may result in death or long-term neurological or developmental disability, particularly following meningitis (WHO, 2026; CDC, 2025A).

The United States follows a universal GBS screening approach. Because routine screening is recommended by both ACOG and ACNM, women receiving standard care from an obstetrician or certified nurse-midwife can generally expect to be offered testing. Pregnant women are typically screened during each pregnancy between 36 weeks 0 days and 37 weeks 6 days. Testing involves gently swabbing the lower vagina and rectum and sending the sample to a laboratory for culture. It is performed late in pregnancy because GBS can come and go, making a late-pregnancy result more likely to reflect whether GBS is present around the time of birth. However, these tests still have meaningful limitations in predicting GBS status at delivery. Skip to “Margins of Error” below for more on this (ACOG, 2020; CDC, 2025D).

Margins of Error

Screening practices may differ among independently practicing community-based or traditional midwives. Current national data specifically describing these practices are limited, so parents should ask their individual provider whether routine GBS screening is offered.

Laboratory-confirmed invasive GBS disease means that GBS has been found in the blood, cerebrospinal fluid or another normally sterile body site. Among newborns, invasive GBS most commonly presents as one or more of the following:

Back to Relevant Terminology

Van Dyke et al was a large multistate, population-based study where researchers used the CDC’s Active Bacterial Core surveillance system and evaluated 819,528 births in the surveillance areas during 2003–2004. They analyzed all 254 identified cases of early-onset GBS disease as well as a stratified sample of more than 7,400 unaffected births. Among the 189 term babies who developed early-onset GBS disease, 116 (61.4%) were born to mothers who had screened negative for GBS before delivery (VAN DYKE ET AL., 2009).

This is strong population-level observational evidence because cases were identified through active laboratory- and population-based surveillance across 10 sites rather than a single institution, although it remains observational rather than randomized evidence (VAN DYKE ET AL., 2009). This evidence was acknowledged by the American Academy of Pediatrics (AAP) in their 2019 clinical report Management of Infants at Risk for Group B Streptococcal Disease (AAP, 2019).

A smaller study found the same pattern at a single large Boston hospital. Researchers retrospectively reviewed 67,260 births at Brigham and Women’s Hospital from 1997–2003 and identified 25 culture-confirmed cases of early-onset GBS disease. Seventeen occurred in term babies, and 14 of those 17 mothers (82%) had screened negative for GBS during pregnancy; one additional mother had unknown GBS status. Notably, 8 of the 14 mothers with negative screens also developed intrapartum risk factors for neonatal infection but did not receive antibiotics because their prenatal GBS test had been negative. Because this was a retrospective, single-center study with only 17 term cases, it provides less precise evidence than the larger CDC surveillance study, but its findings are consistent with the population-based data. Both found a substantial proportion of the early-onset GBS cases that continue to occur in the screening era arise after a documented negative prenatal screen (PUOPOLO ET AL., 2005).

In 2017 a systematic review and meta-analysis which included 30 articles involving 20,328 GBS-positive pregnant women, set out to determine the rate of infection for babies born to GBS positive mothers. The mothers studied were not exclusively low risk, healthy mothers. While these mothers were not administered preventative antibiotics for GBS, some may have received them for other indications.

The review found that the estimated risk of a baby developing confirmed invasive GBS infection during the first week after birth was:

1.1% — approximately 11 in 1,000 babies, or 1 in 91.
The 95% confidence interval was 0.6%–1.5%.

These conclusions came from what was largely observational data (RUSSELL ET AL., 2017).

Babies born to positive mothers who were given antibiotics during labor do still have some risk of infection, but it is minimal. The CDC reports this risk to be 0.025% or 1 in 4,000 (CDC, 2025).

The CDC estimates that a baby’s risk of developing early-onset GBS disease without antibiotics is approximately 0.5%. However, this number appears to come from data collected more than 40 years ago among term, GBS-positive pregnancies without additional risk factors. When pregnancies with factors such as prematurity, prolonged membrane rupture or fever were included, the overall rate increased to 1.36%, with an even higher rate among pregnancies that had specific risk factors (BOYER & GOTOFF, 1985; CDC, 1996).

Low-Risk Mothers with No Additional Risk Factors: Risk of Invasive GBS without Antibiotics: 0.5%

There is no high-quality evidence providing a reliable rate of late-onset invasive GBS specifically among babies born to GBS-positive mothers who did not receive intrapartum antibiotics. However, intrapartum antibiotics have only been shown to reduce early-onset disease; they do not protect against late-onset disease, which may be acquired from the mother during or after birth or from nonmaternal hospital or community sources (PUOPOLO ET AL., 2019; CDC, 2025B).

Risk for Babies Born to GBS in Labor for GBS:

Sources listed above with original statistical information; this is a pooled data summary.

Yes. If prophylactic treatment is declined or considered inadequate (less than 4 hours), there is an association with increased newborn testing & NICU admissions (TURRENTINE ET AL., 2013).

In one cohort of more than 4,700 women receiving prophylactic antibiotics, 71% of infants whose mothers received less than four hours of prophylaxis underwent a CBC and 68% had a blood culture. NICU admission was also slightly higher with less than four hours of antibiotic exposure (0.96% vs 0.41%), although overall hospital length of stay did not differ (TURRENTINE ET AL., 2013).

Back to Relevant Terminology

The rapid GBS test is one of the more interesting developments in maternity care because it allows providers to test for Group B Streptococcus during labor, rather than relying exclusively on a test performed weeks before birth, which studies show inaccurately in predicting whether a woman will be colonized when she gives birth (YOUNG ET AL., 2011; ACOG, 2020).

The rapid GBS test is typically a molecular test called PCR (polymerase chain reaction) or, more broadly, a nucleic acid amplification test (NAAT) (ACOG, 2020).

A recent systematic review and meta-analysis of 52 studies involving 24,653 participants reported that rapid PCR tests detected approximately 90% of colonized women, with a 4% false-positive rate among noncolonized women (PÁEZ-CASTELLANOS ET AL., 2026).

When comparing rapid test vs. standard prenatal testing, it's noteworthy that a direct U.S. study found rapid testing during labor identified 90.8% of women colonized at delivery, compared with 69.2% identified by prenatal cultures (PÁEZ-CASTELLANOS ET AL., 2026; YOUNG ET AL., 2011).

The U.S. does not routinely use rapid GBS testing during labor. If someone wants to consider this in addition to prenatal testing, when prenatal results are unknown, or instead of the usual US prenatal testing, they should speak with their provider to find out if this could be an available option. ACOG does not currently recommend rapid intrapartum testing alone as a replacement for routine prenatal screening (ACOG, 2020).

As seen below in A Global Perspective below, some high-ranking countries have incorporated rapid PCR testing into selected maternity care protocols (CHRISTIANSEN, 2024; RAVIJUHEND, 2026).

If a mother is GBS positive, all parents should evaluate the statistical risk above & form their own conclusion as to what their estimated risk is based off their individual known risk factors.

When a mother is colonized with GBS there is always a risk of that bacteria making its way into the uterine environment. However, the risk is very low when the membranes are intact as they serve as a barrier. When those membranes rupture, risk increases over time for the bacteria to ascend and colonize the uterine fluid & the baby which can increase risk of severe illness when/if baby swallows or breathes that fluid. There is also a risk that the placenta may be infected by that bacteria and a bloodstream infection could occur (sepsis) (AAP, 2019; BROKAW ET AL., 2021).

Molecular studies have demonstrated matching GBS organisms in maternal vaginal samples, fetal membranes, amniotic fluid, and neonatal blood, supporting this potential ascending pathway into invasive neonatal infection (PONGCHAIKUL ET AL., 2024).

vaginal GBS → cervix → fetal membranes → amniotic fluid → fetus

What if my baby is in that .5 - 1.36% and develops invasive GBS disease? What are the risk?

We can infer from the Madrid et al 2017 global systematic review, that babies diagnosed with invasive GBS disease, that live in a “developed” nation do have a decreased chance of death (study shows 5% in developed nations compared with the 8.4 - 10% worldwide average). It is important to note: both these statistics are from a review that DOES NOT distinguish between babies born premature and otherwise healthy full-term babies.

The evidence below paints a better picture of term specific risk in developed nations…

This national surveillance study examined diagnosed early-onset invasive GBS cases from 2014–2015 (856 cases) and provided a term-specific estimate:

All these percentages describe death among babies who developed invasive disease—not among babies merely colonized or all babies born to GBS-positive mothers. All cases were documented to have positive sterile-site GBS culture (O’SULLIVAN ET AL., 2019).

Full term healthy baby early-onset fatality risk without antibiotics in labor: 0.0075 x 0.027 = 0.0002025 (.0075 was used as a middle ground between available data presented above)

Estimations are calculated by The Birth Review based off pooled observational data and do not come from a single verified source.

In Stoll et al. (2020), a study at 18 U.S. centers during 2015–2017, intensive-care use among babies with confirmed early-onset GBS was:

(STOLL ET AL., 2020)

This nationwide Norwegian cohort included infants with culture-confirmed invasive GBS and compared their long-term outcomes with more than 1.4 million children in the general population without identified invasive GBS. Among children included in long-term follow-up after early-onset invasive GBS, 15.2% were later diagnosed with at least one neurodevelopmental disorder. The children’s mean age at the end of follow-up was approximately 12 years 10 months (MYNAREK ET AL., 2024).

Long-term diagnoses reported among children who experienced early-onset invasive GBS.

These figures represent absolute percentage-point differences in observed diagnoses between children who survived early-onset invasive GBS and children without identified invasive GBS. They do not establish that GBS caused the additional diagnoses. Categories overlap and cannot be added together (MYNAREK ET AL., 2024).

*This category included diagnosed disorders of speech, language, motor skills and broader psychological development. Categories overlap, so they cannot be added together.

Beta-lactam antibiotics, including penicillin and ampicillin, are the most commonly prescribed antibiotics during labor to prevent GBS disease (CDC, 2025D).

The CDC did not state where these findings came from or provide numbers that represent reactions to all beta-lactam antibiotics (CDC, 2025D).

Antibiotics commonly given during labor for GBS prophylaxis cross the placenta and can alter the infant’s developing gut microbiome. Research involving babies and young children also shows that direct or repeated antibiotic treatment can reduce beneficial bacteria and increase antibiotic-resistance genes. These genes do not reproduce independently; rather, they are copied as resistant bacteria multiply and can sometimes spread between bacteria. This raises concern that resistance may persist, although it remains uncertain whether these early changes cause lasting health effects (ZIMMERMANN & CURTIS, 2020; DUONG ET AL., 2022; REYMAN ET AL., 2022; LUCHEN ET AL., 2023; MORADI ET AL., 2026).

The CDC states, “The antimicrobial-resistant germs survive, multiply and spread to other germs” (CDC, 2025E). The AAP similarly identifies antibiotic resistance as a threat to public health (GERBER ET AL., 2021).

The CDC identified antibiotic resistance and a possible increase in the incidence or severity of non-GBS newborn infections as potential unintended consequences of intrapartum antibiotic prophylaxis, requiring continued surveillance. However, population-level evidence has not confirmed a clear overall increase. Findings among preterm and very-low-birth-weight infants remain mixed and should be studied more (CDC, 2010; SCHRAG ET AL., 2016; LI ET AL., 2020; STOLL ET AL., 2020).

Antibiotic exposure during pregnancy, labor or early childhood has been associated with later asthma, eczema, allergies, obesity, autoimmune-related disease and some neurodevelopmental diagnoses. However, this evidence is observational, not high quality and does not confirm that antibiotics caused these outcomes (DUONG ET AL., 2022; YU ET AL., 2022; LI ET AL., 2023; MORADI ET AL., 2026).

For mothers who test positive for GBS, receiving antibiotics during labor may influence decisions about when to arrive at the hospital. However, research suggests that earlier admission is associated with increased interventions. In a 2023 observational study of first-time mothers, those admitted earlier experienced higher rates of oxytocin augmentation (63.4% vs. 41.8%), epidural use (89.7% vs. 81.5%), and cesarean birth (24% vs. 15.7%) compared with mothers admitted later (KJERULFF ET AL., 2023). While this study did not specifically examine GBS-positive mothers or establish causation, it highlights an important consideration when discussing hospital admission timing and GBS antibiotic administration.

ACOG: Universal screening at 36–37 weeks and IV antibiotics during labor when GBS-positive or otherwise indicated.

WHO: Universal screening at 35–37 weeks and IV antibiotics during labor when positive. Risk-based prevention is acceptable where universal screening is not feasible.

CDC: Follows ACOG’s current guidance—universal screening and IV antibiotics during labor when indicated.

ACNM: Endorses ACOG’s universal-screening and intrapartum-antibiotic guidance.

(ACOG, 2020; WHO, 2024; CDC, 2025D)

(KVALVIK ET AL., 2025; ESTONIAN GUIDELINE WORKING GROUP, 2026; BJÖRKLUND ET AL., 2024; ISS, 2018; JSOG, 2026; SUNDHED.DK, N.D.)

Additional Context: These countries rank in the top 6 based off pooled maternal & neonatal statistics from the OECD. Using that same pooled calculation, the United States is tied for 32nd among the 38 OECD countries with sufficient data (OECD, 2026).

Author’s Note: These countries’ low mortality rates cannot be directly attributed to their approaches to GBS management. However, this comparison does indicate that countries using a risk-based approach do not have higher overall neonatal mortality.

All expectant parents have the right to do a risk vs. risk evaluation and decide what risk you are most comfortable being susceptible to. Although universal screening is standard procedure in the US, parents have the right to decline screening if desired or to do a risk-based approach. Parents may also decline intrapartum antibiotics if desired. Parents also have the right to request a follow up test closer to delivery, if time permits. Parents should consider providers flexibility & willingness to respect an informed parental choice as a part of their provider selection considerations.