Pregnancy and Group B Streptococcal Infection

Group B streptococci (GBS), or Streptococcus agalactiae, are bacteria commonly found in the vagina, rectum or bladder.

Normally present in the digestive tract, group B streptococcus is not pathogenic. However, this bacterium can sometimes colonise the genital area of expectant mothers — and this is where it becomes dangerous. Group B streptococcus can then be transmitted to the foetus during pregnancy, as well as during labour[1]. Screening is carried out by means of a vaginal swab between 34 and 37 weeks of pregnancy.

What are the symptoms during pregnancy?

Women with group B streptococcus often have no symptoms (in nearly half of cases)[2]. Sometimes there may be clinical signs such as a burning sensation in the vagina.

Outside of pregnancy, group B streptococcus can sometimes also be responsible for mild infections that are easily treated with standard antibiotics.

This bacterium often causes no problems for the mother; however, if it goes on to infect the newborn, rare but serious complications may develop.

Who carries it?

In pregnant women, carriage rates vary, but it is estimated that: approximately 10 to 30% are carriers[3]; in France, this represents 10%, or at least 75,000 per year[4].

Of these, approximately 40 to 70% transmit the bacteria to their baby during labour, and 1 in 2,000 newborns will develop an infection[5].

It is not yet known why some women become carriers and others do not. This may be due to a genetic predisposition and/or an imbalance in the microbiome, as we shall see below.

A positive Group B Streptococcus test result is not a contraindication to breastfeeding.

For the newborn: 

"Group B streptococcus is the leading cause of neonatal infection," notes Professor Claire Poyart, Head of the Bacteriology Department at Cochin Hospital (APHP) and Director of the National Reference Centre for Streptococci. It can cause miscarriages as well as premature births [6].

According to one study, 57,000 miscarriages worldwide per year are attributable to the bacterium [7]. It is also thought to be responsible for 3.5 million premature births [7].  

In the event of infection, the newborn may develop a severe illness. This most commonly manifests as septicaemia (a systemic infection of the body) and respiratory distress (the inability of the lungs to function properly). Sometimes these symptoms are accompanied by inflammation of the membranes surrounding the brain (meningitis). It can be responsible for the death or disability of infants.

The child may be infected at birth or later, generally around 3 weeks after delivery. Approximately 300,000 children are affected worldwide each year [8]. In France, 500 cases of invasive neonatal infections associated with group B streptococcus are recorded every year. These cause between 50 and 100 deaths [9].

For the mother: 

For the mother after delivery, the infection can cause a urinary tract infection, endometritis (infection of the inner lining of the uterus), septicaemia, or chorioamnionitis (infection of the placental tissues and amniotic fluid).

When the mother is infected, certain factors increase the likelihood of the infection being transmitted to the baby, including:
- Induction of labour or rupture of membranes before 37 weeks of pregnancy
- Rupture of membranes when labour begins at the expected date and is likely to last more than 18 hours
- Unexplained mild fever during labour
- History of a birth where Group B Streptococcus was transmitted to the baby
- Presence of GBS in the urine or bladder infection caused by GBS.

The first signs of Group B Streptococcus infection in a newborn are: 
- fever
- irritability
- lethargy
- breathing difficulties
- bluish tint to the skin
 - difficulty feeding.

The Haute Autorité de Santé recommends that expectant mothers undergo routine screening for Group B Streptococcus carriage during pregnancy, between weeks 34 and 37. This vaginal swab is most commonly taken during the last gynaecological check-up. It should also be carried out in cases of premature labour or premature rupture of membranes.

The test is simple and painless; it involves taking a swab from the vagina and rectum using a cotton bud. The swab is then cultured to check for the presence of GBS.
 

Even if you are planning a caesarean, you should still have a screening test in case your waters break or labour begins before the scheduled date.

If you have or show any of the symptoms mentioned above, you will receive intravenous antibiotics during labour or if your waters break before term. This strategy significantly reduces infections at birth. Oral antibiotics and antibiotics taken before delivery have been shown to be ineffective in preventing the transmission of group B streptococcus. They must be taken during labour; otherwise there is a risk of the bacteria returning.

The HAS recommends antibiotic treatment in the following cases: 
- In the event of a diagnosis of GBS carriage during pregnancy, whether close to or distant from delivery;
- In the event of GBS bacteriuria during pregnancy;
- In the event of a history of neonatal GBS infection;
- In the absence of a vaginal swab screening for GBS, if 1 of the following risk factors is present: delivery occurs before 37 weeks of gestation, the duration of membrane rupture exceeds 12 hours, or the maternal temperature exceeds 38°C during labour. 
- If you have a history of maternal-foetal GBS infection or presented GBS bacteriuria during pregnancy, antibiotic treatment will be mandatory. 
 

If the bacterium is detected at birth in the newborn, an antibiotic is also administered to the infant intravenously during the first 48 hours of life.
However, the infection may develop within 7 days of birth, or even later. And in those cases, treatments are less well established.
Vaccines against group B streptococcus are under investigation, but no real prospects yet…

There are risk factors we cannot act upon — for example, age and underlying conditions such as diabetes or cancer are potential risk factors.

We can try to reduce the risk of infection by looking after our microbiome. These approaches are inexpensive and easy to implement.

Beyond the risks to you and your baby, if you test positive, you will receive antibiotic treatment during labour. 

The microbiome is established at birth through a process called bacterial colonisation. During a vaginal birth, the baby passes through the vaginal mucosa, which is colonised by billions of bacteria. This exposure therefore acts as a "first vaccine", allowing the baby to develop its immunity.

Studies have shown that the mode of delivery has a decisive impact on the baby's microbiome. Children born vaginally at home and exclusively breastfed have a greater number of "beneficial" bacteria [14]. The most notable differences are seen in bacteroides, which are thought to have a positive influence on the immune system and are considered to help reduce inflammation [15].

To find out more, all see our article on the infant microbiome.

When you take a course of antibiotics, all bacteria are killed, including the beneficial ones. A study[16] on mothers who received antibiotics following a GBS infection showed that their babies had a different microbiome (fewer beneficial bacteroides, far too many enterococcus and clostridium), and that these differences persisted even more if the baby was born by caesarean section. But the good news is that breastfeeding appeared to correct some of these effects (less clostridium, more lactobacillus)!

I tested positive — is there anything I can do?
You can try following these tips for at least 2 weeks and ask to be retested, if possible. The idea is to develop the right bacteria and boost your immune system. At best, you will have reduced the risk of transmitting the bacteria to your baby in the event of vaginal examinations, of membrane sweep, and in general during labour!