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Group B Streptococcus (GBS)
First Years Pregnancy Sep 24, 2019
8 Minutes

Protecting your baby from Group B Streptococcus (GBS)

We are rapidly learning that many of the billions of bacteria in our gut play a very important role in our health. We also know it impacts the health of our babies/future babies. Click here for more. However, not all of this bacteria is good. Enter Group B Streptococcus (GBS). 

This particular bacteria can in fact pose quite significant risk to new babies and is something every parent-to-be should know about. In this article we will go through what it is, how it can impact a very young baby and most importantly what you can do to prevent a very serious infection. 

So: what is this and why should we care about it? 

Research suggests a range of between 12-36% of the population globally have colonisation with GBS. Within the gut and genital tract. In the US for example, the CDC estimates it to be carried by approximately 25% of pregnant women (3). 

Not entirely uncommon. So, what is the problem then? 

The reality is that it can be an entirely normal part of the human microflora (1, 7). It can be persistent (ie. always there in your system) or can even come and go over time. Typically, as an adult with a decent immune system, you will have no symptoms at all. In fact, most people don’t even know it is there. The trouble comes with new babies. Unfortunately its presence can potentially cause life threatening infections (3). This is where we have much more of an issue….


Now, before you panic. Don’t. 

Here is what you need to know:

New babies, especially ones that are premature, do not have very well developed immune systems. In fact, research suggests they are generally deficient in circulating levels of antibodies to Group B Streptococcus (GBS) in particular (6) which is why this can be a problem. Unfortunately, getting this particular bug early on, can lead to anything from premature birth, to stillbirth to meningitis and pneumonia. In fact, GBS is the number one cause of sepsis and meningitis in new babies (2, 4). It is also the leading cause of infant death, particularly in the first week (1). 

Once again: don’t panic, this is where knowledge is a great thing and the good news is a lot we can do to prevent this from occurring: 

A few factoids to set the scene: 

How can this affect a baby? When it comes to what is known as ‘Group B Streptococcus (GBS) early onset’ (which is when a baby gets an infection in the first six days). What we do know is that the mother needs to have it within the gastro or genital tract to pass it on. (2) 

Ok, so first step: check that.

More good news? This is easy to do…

When does the infection actually happen? We know that transmission comes during or just prior to birth. If fact, colonization of the mother is the most important risk factor for this type of infection (2, 3).

So: we know roughly when infection will occur: during birth. What is slightly less clear is when it comes to the role of GBS in preterm birth as research suggests that can potentially play a role. (5) 

The good news:

A simple swab test can tell you if you have an infection. After that, if you do test positive for GBS colonization, then a dose of antibiotics during labour can protect your baby. Great! 

So: what about the test? Will you get it? What to expect: 

35 countries now offer this test as standard to pregnant women (hooray!). Always worth asking/checking with your healthcare provider if you get offered a test as standard. Unfortunately, under the NHS, the UK for example does not currently offer this test as standard. Resource is always an issue of course. One of the reasons that it may not be offered as standard is the fact that if a baby gets the bacteria it does not always mean they will get a serious infection. It just increases the risks. So some countries prefer what is known as a ‘risk-based’ approach ie. you will only be screened if you have several other identified risk factors. These increased risk factors can be things like a previous case of Group B Streptococcus (GBS) infection or premature birth for example. 

The stats tell us this

50% of babies born to women who test positive for GBS will become colonised themselves (7). Not all babies will pick it up, and not all babies that acquire it will get a serious infection. However, around 2% of them will develop infection as a result, and this can be variable in its severity with around 80% getting sepsis, 10% pneumonia, 7% meningitis and/or a combination of these. (7) Unfortunately, according to data published in the UK (who do not offer standardised screening) around 43 babies a month are affected by an infection caused by GBS (8). So, it is absolutely something to be aware of and to talk to your doctor about if you are concerned. 

The test itself: some pretty compelling data… 

The US is an interesting example of progress when it comes to dealing with GBS. Over the years the policies have changed and have actually strengthened after new data found that universal screening for Group B Streptococcus (GBS) was more than 50% more effective at preventing the disease compared to the risk based approach (ie. doctors analysing who was most at risk and testing accordingly) (5). This is one of the reasons that the US (and other countries) now offer the test as standard to everyone. 

The current recommendation in the US and other countries is a rectal and vaginal swab at between 35 and 37 weeks of pregnancy (2). Pretty simple. 

So simple to do in fact, that in some instances you can even do at home yourself with a self-test kit.  One research paper demonstrated that doing it at home yourself was almost as effective as a doctor/nurse doing it for you with the test showing 98.4% sensitivity among more than 250 women who did the test themselves. (7) Pretty easy then. 

What happens if you do test positive for GBS colonization? 

Once again – some good news – if you know what you’re dealing with, then it is very easy to prevent a problem developing. The first port of call is a discussion with your doctor. However one study showed that 100% of the women who had antibiotic treatment prevented colonisation in their babies. Against this, 58% of women who did not have treatment passed it onto their babies. (6) 

The results are very good and this strategy has significantly reduced the incidence of early onset infection in the European countries who have the screening policy and in the US (2). In fact, in the US, an active population based surveillance showed an 80% reduction between 1993 and 2008 of GBS infection after its introduction (2). With incidence dropping from 2 in every 1000 babies being born in 1990 to just 0.2 in every 1000 in 2015 (4). Pretty good going! 

So, how does treatment work?

Pretty simple: if you have a positive test result, your doctor can administer antibiotics during labor (something known as intrapartum antibiotic prophylaxis). Over a four hour period. Worth noting that research suggests it is effective during labor rather than being administered before. (8). 

The downside?

As we know nothing is perfect (alas!). The most obvious downside is with administration of antibiotics. Antibiotic resistance is a real risk anytime you give antibiotics (6). The other issue is not only will it stop transmission of GBS but it will also potentially interfere with the transfer of good bacteria from the mother to the child. However, when used correctly, antibiotics can of course be life saving and that is certainly the case with potential GBS infections in very young babies. As it stands it is the only way to effectively prevent it (5) and data has shown how effective this treatment can be. It is always worth a full and frank discussion with your doctor on your options. 

The second issue is that because GBS colonization can come and go in people, you can get a negative reading at 35 weeks for example but then be colonised by the time of birth. So, it is not entirely fail-safe. As one research paper put it:

‘Infants can be impacted even when mothers have screened negative for GBS because of changes in maternal colonization status during the time between screening and delivery or by incorrect test or lab error’ (5) 

This is much less common however with one centre reporting only 14 cases of this over an eight year period with on average only around 7% of women screening negative for GBS subsequently identified as positive by time of delivery (5). 

Bottom line?

As always, we are firm believers in prevention and knowledge of your own individual circumstance being your ultimate friend. The test is very simple to do and will give you an indication if you are more at risk or not. Even better, in some countries (the US for example) it is offered as standard so make sure you get yours done. If you do test positive, then you/your doctor may decide that antibiotics during labour is the best form of action. Forewarned is at least forearmed so the very first thing to do is to check with your healthcare provider if you get it offered and speak up if you’re concerned. Knowledge is power after all!


(1) Lawn JE, Bianchi-Jassir F, Kohli-Lynch M: Group B Streptococcal Disease Worldwide for Pregnant women, stillbirths, and children: Why, what and how to undertake estimates? Clinical Infectious Diseases: Vol 65 Issue 2 (Nov) 2017 S89-S99 

(2) Huang J, Lin XZ, Xhu Y, Chen C: Epidemiology of Group B streptococcal infection in pregnant women and diseased infants in mainland China. Pediatrics and Neonatology: 2019 Jun 26. 

(3) Rosen G, Randis TM, Ratner AJ: Group B Streptococcus and the Vaginal Microbiota: The Journal of Infectious Diseases: 2017 Sept 15: 216(6): 744-751

(4) Puopolo KM: Early-onset group B strep: New guidance includes changes in dosing, assessment: AAP Pediatrics: July 2019.

(5) Puopolo KM, Lynfield R, Cummings JJ, Committee on Fetus and Newborn, Committee on Infectious Diseases: Management of Infants at Risk for Group B Streptococcal Disease: AAP Pediatrics: August 2019, Vol 144 

(6) Koenig JM, Keenan WJ: Group B Streptococcus and Early-Onset Sepsis in the Era of Maternal Prophylaxis: Pediatric Clin N. Am 56 (2009) 689-708

(7) Ahmadzia H.K, Phillips Heine R: Diagnosis and Management of Group B Streptococcus in Pregnancy: Obstetrics Gynecology Clin N Am 41 (2014) 629-647



This article is for informational purposes only. This article is not, nor is it intended to be, a substitute for professional medical advice, diagnosis, or treatment and should never be relied upon for specific medical advice. The information on this website has been developed following years of personal research and from referenced and sourced medical research. Before making any changes we strongly recommend you consult a healthcare professional before you begin.

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