A vaginal birth after caesarean (known as a VBAC) is when a woman who has had a caesarean has a vaginal birth down the track.

In Australia, about 12% of women have a vaginal birth for a subsequent baby after a caesarean. A VBAC is much more common in some other countries, including in several Scandinavian ones, where 45-55% of women have one.

So what’s involved? What are the risks? And who’s most likely to give birth vaginally the next time round?

What happens? What are the risks?

When a woman chooses a VBAC she is cared for much like she would during a planned vaginal birth.

However, an induction of labour is avoided as much as possible, due to the slightly increased risk of the caesarean scar opening up (known as uterine rupture). This is because the medication used in inductions can stimulate strong contractions that put a greater strain on the scar.

In fact, one of the main reasons women may be recommended to have a repeat caesarean over a vaginal birth is due to an increased chance of her caesarean scar rupturing.

This is when layers of the uterus (womb) separate and an emergency caesarean is needed to deliver the baby and repair the uterus.

Uterine rupture is rare. It occurs in about 0.2-0.7% of women with a history of a previous caesarean. A uterine rupture can also happen without a previous caesarean, but this is even rarer.

However, uterine rupture is a medical emergency. A large European study found 13% of babies died after a uterine rupture and 10% of women needed to have their uterus removed.

The risk of uterine rupture increases if women have what’s known as complicated or classical caesarean scars, and for women who have had more than two previous caesareans.

Most care providers recommend you avoid getting pregnant again for around 12 months after a caesarean, to allow full healing of the scar and to reduce the risk of the scar rupturing.

National guidelines recommend women attempt a VBAC in hospital in case emergency care is needed after uterine rupture.

During a VBAC, recommendations are for closer monitoring of the baby’s heart rate and vigilance for abnormal pain that could indicate a rupture is happening.

If labour is not progressing, a caesarean would then usually be advised.

Why avoid multiple caesareans?

There are also risks with repeat caesareans. These include slower recovery, increased risks of the placenta growing abnormally in subsequent pregnancies (placenta accreta), or low in front of the cervix (placenta praevia), and being readmitted to hospital for infection.

Women reported birth trauma and post-traumatic stress more commonly after a caesarean than a vaginal birth, especially if the caesarean was not planned.

Women who had a traumatic caesarean or disrespectful care in their previous birth may choose a VBAC to prevent re-traumatisation and to try to regain control over their birth.

We looked at what happened to women

The most common reason for a caesarean section in Australia is a repeat caesarean. Our new research looked at what this means for VBAC.

We analysed data about 172,000 low-risk women who gave birth for the first time in New South Wales between 2001 and 2016.

We found women who had an initial spontaneous vaginal birth had a 91.3% chance of having subsequent vaginal births. However, if they had a caesarean, their probability of having a VBAC was 4.6% after an elective caesarean and 9% after an emergency one.

We also confirmed what national data and previous studies have shown – there are lower VBAC rates (meaning higher rates of repeat caesareans) in private hospitals compared to public hospitals.

We found the probability of subsequent elective caesarean births was higher in private hospitals (84.9%) compared to public hospitals (76.9%).

Our study did not specifically address why this might be the case. However, we know that in private hospitals women access private obstetric care and experience higher caesarean rates overall.

What increases the chance of success?

When women plan a VBAC there is a 60-80% chance of having a vaginal birth in the next birth.

The success rates are higher for women who are younger, have a lower body mass index, have had a previous vaginal birth, give birth in a home-like environment or with midwife-led care.

For instance, an Australian study found women who accessed continuity of care with a midwife were more likely to have a successful VBAC compared to having no continuity of care and seeing different care providers each time.

An Australian national survey we conducted found having continuity of care with a midwife when planning a VBAC can increase women’s sense of control and confidence, increase their chance to be upright and active in labour and result in a better relationship with their health-care provider.

Why is this important?

With the rise of caesareans globally, including in Australia, it is more important than ever to value vaginal birth and support women to have a VBAC if this is what they choose.

Our research is also a reminder that how a woman gives birth the first time greatly influences how she gives birth after that. For too many women, this can lead to multiple caesareans, not all of them needed.

Hannah Dahlen, Professor of Midwifery, Associate Dean Research and HDR, Midwifery Discipline Leader, Western Sydney University; Hazel Keedle, Senior Lecturer of Midwifery, Western Sydney University, and Lilian Peters, Adjunct Research Fellow, Western Sydney University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Have you ever wondered why most disinfectants indicate they kill 99.9% or 99.99% of germs, but never promise to wipe out all of them? Perhaps the thought has crossed your mind mid-way through cleaning your kitchen or bathroom.

Surely, in a world where science is able to do all sorts of amazing things, someone would have invented a disinfectant that is 100% effective?

The answer to this conundrum requires understanding a bit of microbiology and a bit of mathematics.

What is a disinfectant?

A disinfectant is a substance used to kill or inactivate bacteria, viruses and other microbes on inanimate objects.

There are literally millions of microbes on surfaces and objects in our domestic environment. While most microbes are not harmful (and some are even good for us) a small proportion can make us sick.

Although disinfection can include physical interventions such as heat treatment or the use of UV light, typically when we think of disinfectants we are referring to the use of chemicals to kill microbes on surfaces or objects.

Chemical disinfectants often contain active ingredients such as alcohols, chlorine compounds and hydrogen peroxide which can target vital components of different microbes to kill them.

The maths of microbial elimination

In the past few years we’ve all become familiar with the concept of exponential growth in the context of the spread of COVID cases.

This is where numbers grow at an ever-accelerating rate, which can lead to an explosion in the size of something very quickly. For example, if a colony of 100 bacteria doubles every hour, in 24 hours’ time the population of bacteria would be more than 1.5 billion.

Conversely, the killing or inactivating of microbes follows a logarithmic decay pattern, which is essentially the opposite of exponential growth. Here, while the number of microbes decreases over time, the rate of death becomes slower as the number of microbes becomes smaller.

For example, if a particular disinfectant kills 90% of bacteria every minute, after one minute, only 10% of the original bacteria will remain. After the next minute, 10% of that remaining 10% (or 1% of the original amount) will remain, and so on.

Because of this logarithmic decay pattern, it’s not possible to ever claim you can kill 100% of any microbial population. You can only ever scientifically say that you are able to reduce the microbial load by a proportion of the initial population. This is why most disinfectants sold for domestic use indicate they kill 99.9% of germs.

Other products such as hand sanitisers and disinfectant wipes, which also often purport to kill 99.9% of germs, follow the same principle.

Real-world implications

As with a lot of science, things get a bit more complicated in the real world than they are in the laboratory. There are a number of other factors to consider when assessing how well a disinfectant is likely to remove microbes from a surface.

One of these factors is the size of the initial microbial population that you’re trying to get rid of. That is, the more contaminated a surface is, the harder the disinfectant needs to work to eliminate the microbes.

If for example you were to start off with only 100 microbes on a surface or object, and you removed 99.9% of these using a disinfectant, you could have a lot of confidence that you have effectively removed all the microbes from that surface or object (called sterilisation).

In contrast, if you have a large initial microbial population of hundreds of millions or billions of microbes contaminating a surface, even reducing the microbial load by 99.9% may still mean there are potentially millions of microbes remaining on the surface.

Time is is a key factor that determines how effectively microbes are killed. So exposing a highly contaminated surface to disinfectant for a longer period is one way to ensure you kill more of the microbial population.

This is why if you look closely at the labels of many common household disinfectants, they will often suggest that to disinfect you should apply the product then wait a specified time before wiping clean. So always consult the label on the product you’re using.

Other factors such as temperature, humidity and the type of surface also influence how well a disinfectant works outside the lab.

Similarly, microbes in the real world may be either more or less sensitive to disinfection than those used for testing in the lab.

Disinfectants are one part infection control

The sensible use of disinfectants plays an important role in our daily lives in reducing our exposure to pathogens (microbes that cause illness). They can therefore reduce our chances of getting sick.

The fact disinfectants can’t be shown to be 100% effective from a scientific perspective in no way detracts from their importance in infection control. But their use should always be complemented by other infection control practices, such as hand washing, to reduce the risk of infection.

Hassan Vally, Associate Professor, Epidemiology, Deakin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.