Group B Strep (GBS) is a bacteria that many of us carry. Most of the time it doesn’t cause any problems. Very occasionally, a newborn baby can become infected with this bacteria and become ill. Even more occasionally, GBS disease can lead to serious illness or be fatal.
Pregnant women are offered screening and treatment for GBS, but this is controversial. On this page, I’ll explain why, and link to some recent evidence on this topic.
I have written a book called Group B Strep Explained, for those who want to know more about this area, the evidence, and their options.
Why is GBS screening controversial?
There are several elements to understanding why GBS screening and treatment is controversial.
As I explained above, GBS disease affects only a very small number of babies, but it can sometimes be serious or fatal.
We can screen women/babies to decide who might be at higher risk, but the rarity of GBS disease and the bluntness of the current screening methods mean that we end up offering unnecessary and potentially harmful treatment (in this case intravenous antibiotics during labour) to hundreds of thousands of women/babies.
The problem with antibiotics
As I will discuss further below, we don’t have good evidence that antibiotics are beneficial.
But antibiotics are known to have a number of downsides, including that they negatively affect our and our babies’ microbiomes. (More on this below).
Current approaches to GBS mean that we are giving antibiotics to many thousands of people who don’t benefit from them, when we don’t have evidence that this helps reduce mortality from GBS disease.
It’s your decision
Like everything, it’s your decision whether to have screening and/or treatment for GBS, but parents have to weigh up difficult decisions in the absence of good evidence.
This page summarises some of the key studies on this topic from the past few years.
If you would like more information and to explore the wider issues so you can make the decisions that are right for you, see my book, Group B Strep Explained.
The benefits and harms of screening and antibiotics
The most recent paper on this topic is a review of the evidence by Campbell et al (2026). They set out to, “…synthesise evidence on the effectiveness, harms and benefits of different approaches to prevent early-onset Group B Streptococcus (EOGBS) and identify gaps in short and longer-term outcomes.”
Let’s look at what they found…
The evidence quality is poor
The most striking finding is how weak the underlying evidence actually is. Of six systematic reviews that the authors initially identified, three were excluded for being critically low quality. The remaining three rated the certainty of evidence as being “…low to very-low certainty” (Campbell et al 2026) across almost all outcomes.
The authors also noted that some potentially relevant neonatal outcomes weren’t included in some of the studies, and that, “Protocol violations and missed opportunities were reported.” (Campbell et al 2026). This is a very weak foundation on which to base screening recommendations.
I also want to mention that the definitions of “universal screening,” “risk-based,” and “no strategy” varied so substantially across studies that the authors themselves caution against direct comparison. Studies classified as the same “type” of approach were often implementing quite different things. This is another significant methodological flaw in the evidence base.
The “universal screening is better” conclusion is shakier than it appears
While the abstract and headlines from this study suggest that universal screening outperforms risk-based approaches, mortality outcomes showed no difference between universal and risk-based strategies. The additional reduction from universal screening is in GBS incidence rates, not in mortality, which is arguably the outcome that matters most to women and families
Women are almost entirely absent from this research
Only one study in 78 reported women’s views or perspectives. Now I don’t know about you, but I find this unacceptable. The review authors themselves flag this as a serious gap.
This isn’t new, and it’s a common finding in research into obstetric intervention.
But the lack of good data in this area is particularly striking given that the intervention being studied involves administering antibiotics to women during labour, which has very real physical consequences, and significantly affects women’s experiences of birth and maternity care. More on this below.
The antibiotic harms are underexplored
Long-term child health outcomes were reported in fewer than ten per cent of the studies. The authors acknowledge a recent meta-analysis linking intrapartum antibiotic (IAP) exposure to modestly increased BMI and autoimmune disease risk, but none of the screening comparison studies actually followed children long enough to assess this.
It is clear from research in other areas that interventions such as antibiotics can have a long term impact on our children. It is equally clear that exploring this impact is not the focus of most medical research.
False negatives undermine the logic of universal screening
Even with universal screening, the approach which leads to the highest number of women being offered antibiotics in labour, 24.2% of EOGBS cases occurred in babies born to mothers with negative cultures. By contrast, risk-based approaches missed 41.3%.
So while universal screening does perform better, it still misses roughly one in four cases, as well as having potential harms. This limitation is rarely discussed when screening is presented to women.
The take-home message
This summary only scratches the surface, of course.
There is a lot more to know about this topic, which is why I wrote a book to explain the issues relating to Group B Strep rather than sticking with a blog post.
But the authors of this study themselves highlight some of the very real problems with our knowledge in this area.
We need better reporting of women’s perspectives, implementation science research to understand real-world failures, longer-term follow-up of children, and approaches to evaluate medium and long-term outcomes.
In other words, they acknowledge that the current evidence base cannot answer the questions that matter the most.
Let’s look at what the authors of some of the other papers on this topic have found in recent years.
GBS and the risk of perinatal morbidity and mortality following term labor
In a paper titled, Group B Streptococcus and the risk of perinatal morbidity and mortality following term labor, Stephens et al (2023) summarise their review of the evidence relating to screening and treatment for GBS.
Like many reviewers before them, they begin by noting that:
“There is currently an absence of level 1 evidence (ie, from randomized controlled trials) that a program of screening and intervention for GBS reduces the risk of neonatal sepsis.” (Stephens et al 2023).
Yet hundreds of thousands of women are given antibiotics in labour, affecting their and their babies’ microbiomes.
As Stephens et al (2023) show, “In the United Kingdom … it is estimated that 440 women need to receive IAP to prevent 1 case of EOD, and 3000 to prevent 1 case of EOD leading to death or severe disability.” (Stephens et al 2023).
Which approach is best?
Some people and charities have been calling for the UK to adopt universal screening, which is used in some other countries, such as the USA.
However, “…the incidences of EOD in United States and United Kingdom are currently comparable.” (Stephens et al 2023).
In other words, there is no evidence that the US approach is better. However, this may be partly because, as above, there is no evidence of benefit from RCTs of either approach.
Adopting universal screening would mean that even more women and babies were exposed to antibiotics:
“Moreover, modeling indicates that if universal screening was implemented in the United Kingdom, >100,000 additional women a year in the United Kingdom would receive IAP, the number needed to treat to prevent a single case of EOD would be approximately 1000, and approximately 7500 women would need to be treated to prevent 1 case of EOD leading to death or severe disability.
Consequently, in the vast majority of cases where IAP is given, the costs and risks would be incurred without clinical benefit. Moreover, widespread use of IAP and the much greater numbers needed to prevent a case of severe EOD contradict other public health initiatives that aim to reduce overall antibiotic use to address the global issue of antimicrobial resistance. (Stephens et al 2023).
Other options…
The paper discusses other approaches that are being explored by medical researchers, such as the possibility of in-labour testing and a GBS vaccine. But these are not without problems either.
Stephens et al (2023) discuss how difficult it would be to test a vaccine, “…given that early-onset disease affects approximately 1 in 1000 births.” (Stephens et al 2023).
And in studies which have looked at rapid or bedside testing in labour, such as the GBS2 trial, the rapid test did not reduce the rate of antibiotics administered to mothers with risk factors, compared to usual care. Newborns did appear to be less exposed to antibiotics with the rapid test than with usual care, but there were issues with accuracy.
Of even more concern is that the study flagged an antibiotic resistance signal in infants that warrants serious attention. Furthermore, even the researchers acknowledged that women can feel pressured when offered testing in labour, and that this hasn’t been fully explored.
Potential harms of GBS screening “outweigh benefits”
A 2019 review published in the British Medical Journal considered the harms of GBS screening as well as the benefits.
And the authors concluded that, based on current evidence, routine screening for group B streptococcus colonisation in late pregnancy should not be introduced in the UK, as the potential harms of unnecessary treatment with antibiotics may outweigh the benefits.
Farah Seedat et al (2019) explain the background to their review:
“The media and politicians regularly call for universal antenatal screening for GBS as an alternative means of selecting women for prophylaxis.
Advocates point to countries across Europe and North America where screening is recommended and where reductions in early onset GBS infection have been observed.
But the evidence shows that the effectiveness of screening, using established screening criteria, is uncertain and that screening has potential harms.
Here, we explain why the UK National Screening Committee decided not to introduce routine screening in the UK—namely, high levels of overtreatment, unknown potential hazards from screening and intrapartum antibiotic prophylaxis treatment, and uncertain benefit.” (Seedat et al 2019).
Concern about overtreatment
I want to return to the issue of overtreatment, as this is of deep concern to many women and those who care for them during pregnancy and childbirth.
When I last updated Group B Strep Explained, I sought input from women, midwives, doctors and other birth workers. Although I heard from a few people who feel strongly in favour of increased screening and treatment (often based on their own experiences of having a baby with GBS disease), the overwhelming majority of comments received were from people who feel that taking the universal screening approach is “too much”.
It is clear that there is serious concern about overtreatment, from women, families, clinicians, and researchers.
Some women who are offered antibiotics because they have risk factors do not want them in those circumstances either, because they are concerned about side effects and the impact of this treatment on a number of aspects of the woman’s and baby’s health and experience.
Concerns about overtreatment
Many of the parents who have contacted me about this topic over the years are also aware that the chance of a baby getting GBS disease is very small, which means the chance of overtreatment is extremely high.
The 2019 analysis showed that:
“…in 2014-15, under risk based prevention, 138 933 term pregnant women were colonised with GBS, but only 350 term neonates developed early onset infection, meaning screening would have led to overtreatment of 138 583 (99.75%) women in labour.” (Seedat et al 2019).
This is of particular concern given what we know about the importance of a baby’s microbiome.
As above, giving antibiotics to women in labour can interfere with the development of a baby’s microbiome and, as I note in my book:
“Recent research shows that not only are bacteria beneficial, but they need to be passed on to the baby during birth via its mother’s vagina and have an important part to play in future health, especially relating to the gut and digestion, but in many other areas of wellbeing as well.” (Wickham 2019).
The BMJ review also contains a couple of useful infographics which illustrate the problem of overtreatment.
The problems with GBS screening
In a 2015 debate in the British Journal of Obstetrics and Gynaecology, two respected obstetricians explained why GBS microbial screening should not be routine in pregnancy. They explained why it is so hard to measure the harms and benefits of this.
“In my view there are two main issues that hamper the assessment of harms and benefits of antenatal GBS screening.
The first is the artefact introduced by using GBS culture-positivity when assessing the outcome of the use of IAP [intrapartum antibiotic prophylaxis]. The presence of antibiotic in the baby’s circulation will inhibit the growth of the organism, despite the clinical picture of sepsis. This artefact means we remain uncertain how effective IAP really is.
The second is the huge number of women who require IAP for the small number of symptomatic neonatal infections that are likely to be prevented, with the resulting concerns about the impact that antibiotics given at the time of labour may have on the longer-term outcomes for a large number of babies.
This uncertainly about impact was highlighted by the follow-up of the ORACLE trial (Kenyon et al. Lancet 2008;376:1319–27), but extends well beyond that, with concerns that selection pressure applied to the developing microbiota may have profound long-term health consequences (Bedford Russell & Murch BJOG 2006;113:758–65; Quigley Gastroenterol Hepatol 2013;9:560–69).
Added to which, there is growing international pressure to limit the use of antibiotics in the face of increasing resistance and a lack of new antibiotic development. Being able to identify women and babies who would most benefit from antibiotics would be an important step in balancing the benefits versus harms of such a programme.” (Brocklehurst & Steer 2015).
GBS Screening: what do women think?
I have only found two studies which look at the acceptability of GBS screening to women, but both of them look at women who are already having GBS screening. This means that the views of women who decline screening are never included, which will bias the results significantly.
For instance, the authors of an analysis of the views of women in the GBS2 trial found that:
“…many of the women interviewed were not concerned about being offered a GBS test, were willing to provide a sample and felt positive towards samples being taken to detect GBS.” (Constantinou et al 2024).
This was a small sample of self-selected women. Nobody asked the women who declined to enter the trial about their views. But even among those who had agreed to be in the trial, “[W]omen were concerned that they may be unable to make an informed decision in labour due to time, pain and the prospect of birthing quickly.” (Constantinou et al 2024).
It feels important to remain aware of this, as we know from experience that it is far easier to introduce new interventions than to remove them. This is an area that is contentious, and many studies highlight the fact that GBS screening and prevention methods have risks and downsides as well as potential benefits.
Maternal antibiotics (e.g. for GBS) and imbalance in baby’s gut bacteria
A study published in the BJOG gave us more information about the way in which antibiotics given in labour affect the gut microbiome of the baby. It was welcome and timely because it confirmed that intrapartum antibiotics are associated with infant gut microbiota dysbiosis (or microbial imbalance) in both vaginal and caesarean and vaginal delivery of healthy term babies.
The authors found that breastfeeding can modify some but not all of these effects.
The study included 198 healthy term babies, who were part of the longitudinal Canadian CHILD study. This might not sound a lot to readers used to research involving hundreds or thousands of women or babies, but it’s a good number for a study of this nature, which involved careful measurement of the babies’ fecal samples at 3 and 12 months. Results showed that,
“In this cohort, 21% of mothers received IAP for Group B Streptococcus prophylaxis or pre-labour rupture of membranes; another 23% received IAP for elective or emergency caesarean section (CS).
Infant gut microbiota community structures at 3 months differed significantly with all IAP exposures, and differences persisted to 12 months for infants delivered by emergency CS.
Taxon-specific composition also differed, with the genera Bacteroides and Parabacteroides under-represented, and Enterococcus and Clostridium over-represented at 3 months following maternal IAP.
Microbiota differences were especially evident following IAP with emergency CS, with some changes (increased Clostridiales and decreased Bacteroidaceae) persisting to 12 months, particularly among non-breastfed infants.” (Azad et al 2015).
Why does this matter?
For those who may be newer to this debate, here’s an excerpt from Group B Strep Explained, in which I wrote about the dilemma of antibiotic prophylaxis:
“No-one wants to put babies at unnecessary risk, but the irony is that one of the most significant consequences of current screening and treatment programmes which involve giving antibiotics to large numbers of labouring women whose babies are deemed to be at risk of disease (which is different from definitely having disease) may be that future generations will not have effective antibiotics even for babies who are diagnosed with actual disease.
Another potentially enormous but unquantifiable problem relates to an area that we are only just beginning to understand. I began this book by discussing the relationships between humans and bacteria, and scientists have started to use terms such as the human microbiome in order to discuss the range of microorganisms that live on and within our bodies. Recent research is suggesting that not only are bacteria beneficial, but they need to be passed on to the baby during birth via its mother’s vagina and have an important part to play in future health, especially relating to the gut and digestion, but in many other areas of wellbeing as well (Turnbaugh et al 2007, Collado et al 2012). Scientists and researchers are concerned about the potential risks to antibiotic overuse both in general (Blaser 2011) and to the baby whose mother receives antibiotics in labour (Neu 2007, Broe et al 2014). This latter concern is supported by the research showing that one of the risks of caesarean section is that these bacteria do not get passed on, which can lead to problems in babies (Grönlund et al 1999, Blaser 2011).
The problems arise because antibiotics are not particularly selective, and many beneficial bacteria will be killed by them, which may have considerable but as yet unquantified knock-on effects in both women and babies (Stokholm et al 2013). Antibiotics can create changes in women’s and babies’ gut bacteria and faecal flora which can cause gastro-intestinal problems and these changes might be permanent (Ambrose et al 1985) and they have been associated with an increased chance of postnatal yeast infection in women and babies (Dinsmoor et al 2005). We need more research into this area.” (Wickham 2019).
The authors of the current study have also noted that we need more research, as this is an important area about which we need to learn much more. But their work represents another important step in our knowledge of this area.
We need more research
In fact, the statement “we need more research” applies to every aspect of this area.
But it’s not just research we need.
We need more attention paid to the concerns of women and families.
We need more and better sources of information.
And we need more balance in the conversation.
For more information on this topic:
About the Author: Dr Sara Wickham is an author, speaker, and researcher specialising in pregnancy, birth and maternity care. Her work focuses on evidence-based, woman-centred information and informed decision-making, drawing on more than 30 years of midwifery knowledge and experience.
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