Hundreds of pre-term births could be prevented in the UK every year after scientists developed a way to identify women at high risk of damaging infections during pregnancy.
A routine and proven procedure can then be used to reduce that risk by nearly three quarters, according to a new study.
The ultrasound risk assessment test would benefit those women who had a caesarean section in the late stage of their previous pregnancy, which significantly increases the chances of a premature birth in subsequent deliveries.
An estimated 2,000 to 5,000 women a year become pregnant in the UK who have had a late stage C-section in their previous pregnancy.
In hundreds of cases, the new test would highlight high-risk cases so that action can be taken, while it would also bring some piece of mind to thousands of women found to be at low risk.
“We hope this will help to reduce rates of preterm births and prevent future baby loss,” Amrita Banerjee, of University College London, told i.
C-sections performed late in pregnancy are more likely to scar the cervix. This reduces its ability to function effectively, increasing the risk of the cervix opening up and letting in harmful bacteria, which can cause premature birth.
Now, researchers have found a way to identify those women with problematic scars so that an existing procedure that can be done without an overnight hospital stay can be used to reduce the risk of pre-term birth.
The procedure involves closing the cervix with a stitch, known as a cervical cerclage, reducing the risk of infection and, in turn, premature birth.
“The assessment of C-section scar characteristics and position is easily incorporated into routine antenatal surveillance, taking only an extra minute to perform during transvaginal ultrasound,” said Professor Anna David, also of UCL.
“If, from this, we can identify women [at risk] and put a stitch in place, it reduces the risk of preterm birth massively – improving outcomes for both mother and child,” she said, cautioning that the approach needs to be confirmed in bigger trials, which she is preparing for now.
“Caesarean sections are low risk if you have one in early labour or before labour starts. But couples and midwives need to be aware of the risks of having a C-section in the late stages of labour particularly at full dilatation,” she said.
“It’s important that people know the link between late-stage C-sections and preterm birth so that they can be referred to a clinic for appropriate assessments and interventions to improve their outcomes. The treatment that we have outlined is already available as part of routine NHS care.”
The procedure is already used to reduce the risk of pre-term birth and miscarriage for women who had a previous premature birth, late miscarriage or cervical surgery.
The researchers now want to use it in hundreds of high-risk pregnancies a year that occur after late stage C sections after finding a way to identify those women at at high risk of pre-term birth.
Case study: Katie Bonful
Katie Bonful works in recruitment and lives in Kent with her husband and their three sons, Maximus, Leonidas, and Lucius. She experienced two late miscarriages back-to-back in three years – both on the same day, exactly a year apart.
She has since had three babies with the help of a cervical cerclage – the procedure UCL researchers would now like to see offered to thousands more women a year. She is an ambassador for Tommys, the pregnancy and baby loss charity.
“About nine months ago, when I was three months pregnant I had a cervical stitch, also known as a cervical cerclage. A cerclage is a medical procedure which involves temporarily closing the cervix with stitches.
“This procedure helps to prevent preterm labour, which is when regular contractions result in the opening of your cervix before 37 weeks. Preterm labour can result in premature birth. The earlier premature birth happens, the greater the health risks for your baby.
“I lost my first two babies due to preterm labour. So thankfully the consultant at my hospital recommended I have a stitch for baby B. This is my third time having the stitch and it helped me to have both Maxi and Leo, who were both born at full term.
“The day of the procedure, my husband and I arrived at the hospital early and waited to be seen. I was not allowed anything to eat beforehand, and was given an epidural in my spine, meaning I was numb from the waist down. This part took about 10 minutes as the doctor had to make sure the spinal was going in the right place.
“Having the stitch fitted took about 10 minutes. They also gave me a catheter as I had absolutely no feeling in my legs.
“After the procedure, I stayed in hospital for about five hours to allow the feeling in my legs to return.
“Thankfully the stitch did its job and helped me to stay pregnant and pass my danger zone, which was usually in the second trimester.
“If you have experienced baby loss due to issues with your cervix, as a result of infection or having an incompetent cervix, this procedure may help you to carry to full term.”
The researchers developed a ‘transvaginal’ ultrasound technique and used it to assess the position of the women’s C-section scar in relation to their cervix.
An ultrasound probe was inserted into the vagina and gently moved either side to assess the cervical length and the height of C-section scar.
If researchers were unable to see a c-section scar, then they found that the women were unlikely to have a preterm birth.
However, if the scar was low down the womb or within the cervix then there was a much higher chance of the cervix opening up in mid-pregnancy and of women then delivering preterm.
To reduce the risk of this happening, they put a stitch around the cervix.
“This has the potential to save hundreds of preterm births in the UK a year,” said Siobhan Quenby, Professor of Obstetrics at Warwick University, who was not involved in the research – adding that the new method could bring peace of mind of many pregnant women.
“At the moment we are telling women who have had a previous full dilation c section that they might have a preterm birth next time. This information causes them anxiety. An important findings here is that if we cannot see the C-section scan on ultrasound scan in a subsequent pregnancy we can reassure the woman. If we can see the scar and the cervix is short [due to scarring] we can take preventative actions with a cervical stitch,” she said.
About 15 per cent of women who have a caesarean section in the late stages of labour are at increased risk of preterm birth in subsequent pregnancies – compared with a 2 per cent risk among pregnant women in general.
But using the ultrasound test and cervical cerclage method cut that risk to 4.1 per cent, a risk reduction of 73 per cent, according to a study of 243 pregnant women by University College London, published in the American Journal of Obstetrics & Gynecology MFM.
The researchers are now in discussions with NHS hospitals at universities around England to further demonstrate the technique in the hope that it will one day be used routinely on the health service.
More than a quarter of all deliveries in the UK are by C-section and up to 5 per cent of those occur at full dilatation (10cm) in a late stage of labour.
Professor David estimates that there are between 4,000 and 10,000 full dilatation caesarean sections (FDCS) a year in the UK.
“Of those, even if we said half of all women who have a prior FDCS go onto have another pregnancy that would be at high risk of preterm birth – that is still 2000 to 5000 per year,” she says – about 15 per cent of which are likely to have a preterm birth.
As such, the ultrasound technique could be offered to thousands of women a year and potentially prevent hundreds of pre-term births researchers say.
Andrew Shennan, professor of obstetrics at King’s College London, who was also not involved in the work, added: “It is well established that previous emergency caesareans cause preterm birth and this is related to the scar. This data confirms the height of the scar is important in terms of risk, and suggests we should consider changing technique at caesarean.”
Women have late stage C-sections for a number of reasons, usually in an emergency, such as the baby having heart rate abnormalities or to avoid a difficult ‘instrumental’ delivery, when forceps or a ventouse suction cup are used to help deliver the baby.
A preterm birth is one that happens before 37 completed weeks of pregnancy. There were 53,000 babies born prematurely in 2021, in the UK. In England and Wales, 7.6 per cent of births were preterm.
Although each case is individual, generally, the earlier a child is born, the higher their risk of problems. And around 1 in 10 of all preterm babies will have a permanent disability such as lung disease, cerebral palsy, blindness or deafness.
A spokesperson for Tommys, the pregnancy and baby loss charity, said: “We welcome new tests and treatments like this which can identify those at greatest risk and make sure they get the specialist care they need to give them the best chance of taking a healthy baby home.”
Risk assessment, explained: Professor Anna David, UCL
Why does late C-section increase the risk of a more problematic scar?
As labour progresses, the cervix opens up / dilates more to allow the baby to descend through the pelvis. At full dilatation the cervix is 10cm dilated and has completely effaced (been taken up by the lower part of the uterus called the uterine lower segment). The baby’s head at this stage is very low in the pelvis.
Usually at Caesarean section we aim to cut the uterus within the lower segment, just above the cervix, as this is the part of the uterus that heals up the best. But at late labour stage CS (eg 8-10cm), when we do a Caesarean section, the incision on the uterus ends up being very low down on the uterus and can inadvertently end up being in the cervix itself. Our data suggests that the scar ends up being within 5mm of the top of the cervix in 41 per cent of cases of women having a CS at full dilatation.
When the uterus has been working hard in labour for some time (it is a muscle after all), the cut can extend as the tissues become more delicate so the initial cut can end up resulting in a larger scar. Also the head is often deeply impacted in the pelvis which means that we need to gently pull it back up again to deliver the head through the uterine incision. This can end up causing the scar to extend.
All of the above end up with a scar that is lower down near or in the cervix itself and probably wider. This compromises the function of the cervix which is essentially a tubular structure that closes off the uterus and prevents vaginal bacteria from moving up into the sterile uterus. A scar near the top of the cervix prevents the tube from staying long and closed so that it shortens.
What is meant by the cervix becoming shorter? How does a scar make it shorter? And why does that increase the risk of a preterm birth?
The cervix tends to shorten/open up from its top part called the internal cervical os – this shortening is called funnelling. Once the cervix starts to shorten, the mucous plug, which sits within the tube (endocervical canal), falls out. The mucous plug is a barrier to stop bacteria that normally live in the vagina from ascending into the uterus. Once bacteria enter the uterus and infect the fetal membranes around the fetus, they cause inflammation. This can make the fetal membranes rupture, leading to PPROM (preterm prelabour rupture of the membranes). The inflammation and infection causes the uterus to contract, expelling the fetus before it is due as a preterm birth.
A low scar in or near the cervix increases the likelihood of cervical funnelling/shortening, leading to preterm birth.
How does the stitch help?
The stitch is like a purse-string that goes around and within the cervix to close it. We aim to place it as high as possible in the cervix to support it and prevent funnelling/shortening from the top. If the stitch goes in high up the cervix, it can often close up if it has begun to funnel. If placed early enough, it can stop the mucous plug from falling out of the endocervical canal so that it stops the bacteria from ascending through the cervix to the uterus.