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'Switch stitch' to cut risk of premature birth and neonatal loss

  • 1 Comment

Maternity units should reconsider using a particular type of thread for a procedure to prevent premature birth, say researchers after their study found it was associated with worse outcomes.

Researchers at Imperial College London analysed 671 UK women who received a cervical cerclage procedure because they were deemed at high risk of miscarriage or premature birth.

“We strongly advise that the thicker thread only be used in a research setting while we investigate the risks”

Phillip Bennett

The process involves placing a stitch in the cervix to hold it closed and delay labour. The stitch also prevents bacteria passing through the cervix and into the womb.

The study authors noted that one of two types of thread were used – a thin nylon thread, around 1mm thick, called monofilament, or a thicker thread, around 5mm thick, comprised of smaller threads woven together called multifilament.

The thicker thread is used in around 80% of procedures due to the belief that it is stronger and more efficient at holding the cervix closed.

However, the Imperial study results, published in the journal Science Translational Medicine, suggest the thicker thread was associated with a three-fold increase in the rate of baby death in the womb.

It was also associated with an increased rate of premature birth, said the researchers, who suggested the thicker woven structure of the thread encouraged the growth of dangerous bacteria.

They looked at 671 women who had the procedure at five UK hospitals over the last 10 years. Around half had the thinner thread, while the other half had the thicker thread.

“A safe and proven treatment to prevent pre-term birth has just been made safer by this new finding”

Jane Brewin

The results revealed the thicker thread was associated with increased rate of intrauterine death compared to the thinner thread – 15% versus 5%. The rate in a normal pregnancy is around 0.5%.

The thicker thread was also associated with an increased rate of pre-term birth rate, compared to the thinner thread – 28% versus 17%. The pre-term rate among the general population is around 7%.

To understand the difference in outcomes, the researchers conducted a second study with 50 women due to have cervical cerclage.

They then monitored the women at four, eight and 16 weeks after the procedure through ultrasound scans and analysis of bacteria collected using vaginal swabs.

The results suggested women receiving the thicker thread had increased inflammation around the cervix. There was also increased blood flow, which is linked with the cervix opening before labour.

Crucially, the researchers noted that they found women who received the thicker thread had more potentially harmful bacteria in the vagina and around the cervix.

Study author Dr David MacIntyre said: “At the beginning of the trial, all women had similar types of naturally-occurring bacteria, called Lactobacillus, in their birth canal and around their cervix.

Imperial College London

‘Switch stitch’ to cut risk of premature birth

David McIntyre

“However, four weeks after the procedure 45% of the women who received the thicker thread had these harmless bacteria replaced with potentially dangerous bacteria that have previously been associated with poor outcomes during pregnancy,” he said.

“Women who received the thinner thread maintained normal levels of harmless Lactobacillus bacteria in the birth canal or cervix,” he noted.

The researchers also performed lab-based experiments to examine how easily bacteria grew on the two types of thread.

Dr MacIntyre added: “We found potentially dangerous bacteria grew more easily on the thicker thread. This may be because bacteria can latch onto the woven structure of the thick thread more easily than the smooth thin thread.”

Lead author Professor Phillip Bennett said: “We strongly advise that the thicker thread – which is currently used in the majority of procedures – only be used in a research setting whilst we thoroughly investigate the risks this may hold.”

A new trial of 900 patients is currently underway, organised by University of Birmingham, which is looking at the comparative risks of the two threads.

Tommy's

‘Switch stitch’ to cut risk of premature birth

Jane Brewin

Professor Bennett added: “Only by performing a large randomised clinical trial can we confirm whether the thicker thread itself is triggering complications, to ensure this procedure is as safe and effective as possible for the mother and baby.”

Jane Brewin, chief executive of the charity Tommy’s, said: “The really good news is that a safe and proven treatment to prevent pre-term birth has just been made safer by this new finding.

“A treatment which has been around for many years has been shown to prevent pre-term birth but no-one really understood why it seemed so effective in some people but not in others; now we have a plausible explanation,” she said.

Around 50,000 babies are born prematurely ever year in the UK. Defined as birth between 24 and 37 weeks of pregnancy, premature birth is the leading cause of neonatal death in the UK.

Imperial College London

‘Switch stitch’ to cut risk of premature birth

The thicker multifilament thread (top) compared to the thinner monofilament thread (bottom)

  • 1 Comment

Readers' comments (1)

  • michael stone

    Well,

    'Dr MacIntyre added: “We found potentially dangerous bacteria grew more easily on the thicker thread. This may be because bacteria can latch onto the woven structure of the thick thread more easily than the smooth thin thread.”'

    I'm assuming that bacteria cannot grow inside a nylon thread, so the only place they could grow is on the surface: the potential for more bacterial growth on a thicker woven thread, compared to on a thin mono-filament thread, is surely so obvious, that people would have needed to think about that even before a study such as this one ?

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