Stillbirth is the death of a baby before or during birth after 24 or more weeks of pregnancy. This happens in around one in every 200 births in the UK.
A stillbirth before labour is called an ‘antepartum stillbirth’ and during labour is called an ‘intrapartum stillbirth’.
To date, there has been little research into stillbirth caused by group B Strep, and so there is very little evidence on why it happens and what, if anything, increases the chance of it happening.
This is partly because stillbirths themselves are uncommon, and GBS is not a common cause of them – recent research estimates that GBS accounts for around 1% of antepartum stillbirths in high income countries.
How does group B Strep cause stillbirth?
When a baby is stillborn as a result of group B Strep infection, the baby’s mother will have been carrying group B Strep and the mother’s normal defences against the baby developing an infection will have been breached. This can be for a number of reasons, for example her cervix has dilated, or her waters have gone (often for a prolonged period). But occasionally it happens without any warning signs at all.
It seems likely that GBS manages to get into the womb, either by crossing the membranes from the vagina (the most likely route), or being transmitted via the mother’s circulation (a theoretical risk if the mother herself has an active GBS infection, although this has never been definitively established). The bacteria have already demonstrated their virulence and has overcome the mother’s defences.
We have no way of knowing if some babies get invaded but fight off the infection, because they don’t become ill. If the baby does get infected, sometimes labour will start or the waters will break, so the baby is born quickly and can receive urgent treatment. Tragically, some of these sick babies will die before birth, and sometimes even before the waters break or labour starts.
Stillbirth before labour (antepartum)
A stillbirth before labour is called an ‘antepartum stillbirth’.
There are no known ways to prevent group B Strep-caused antepartum stillbirths. The usual preventative medicine to stop GBS infection in newborn babies is to give intravenous antibiotics to the mother from the start of labour. If a baby dies from GBS infection before labour starts, there are usually no obvious clinical signs of the infection before the baby dies, so there is no opportunity to give the antibiotics.
Stillbirth during labour (intrapartum)
A stillbirth during labour is called an ‘intrapartum stillbirth’.
About one in four babies are exposed to group B Strep around or after birth because their mothers are carrying group B Strep. About half of those babies will become colonised (carry the bacteria) and about one in 200 of those colonised develop infection (infection is when GBS invades their tissues and makes them sick).
We don’t know how many babies will be exposed to GBS before labour starts and when the membranes are still intact. Usually there are no bacteria in the womb antenatally (before labour).
The usual preventative medicine to stop GBS infection in newborn babies is to give intravenous antibiotics to the mother from the start of labour. These antibiotics are highly effective at preventing GBS infection in the newborn baby or, where a baby already is developing infection, they can act as early treatment of the GBS infection.
How to prevent GBS-caused stillbirths
Currently there are no proven ways to prevent stillbirths caused by GBS before labour, although the intravenous antibiotics given in labour or after waters break to women known to be carrying GBS should prevent stillbirths occurring during labour.
We know that giving antibiotics throughout pregnancy ‘just in case’ is not a good idea. It can upset the normal balance of bacteria in the mother (the ‘microbiome’, the community of many different bacteria that live in a healthy person’s bowel/vagina), and this can lead to problems such as thrush (growth of a yeast called Candida albicans). The healthy microbiome keeps the growth of pathogenic (nasty) bacteria in check, and if the microbiome is disturbed, the pathogenic bacteria can multiply rapidly and cause infections. These can be just as catastrophic as group B Strep infection.
In contrast to this known harm, we have no evidence from any study that giving antibiotics antenatally ‘just in case’ would prevent babies being stillborn, or developing GBS infection before birth.
Looking to the future, we anticipate that a vaccine against group B Strep will prevent the majority of group B Strep infection in mothers and babies, including stillbirths and GBS infections contracted during labour and in the first 3 months of life.
Work to develop vaccines is ongoing, but it is not an easy task to produce one because there are ten different strains of GBS and, to be worthwhile, a vaccine has to work against at least five or six strains.