Doctors performing cervical cerclage should use a thin suture rather than the more common thick "shoe-lace" thread, researchers said yesterday.
A London-based study, published last night, suggests the use of the thicker thread is linked to an increased rate of premature birth.
According to the researchers, only 20% of procedures use the thinner thread – but these are one third as likely to lead to the loss of the baby.
They suggest that the thick "shoe-lace" thread causes inflammation and risk of infection compared with thin "fishing line" thread.
According to the researchers at Imperial College, London, use of thin thread could prevent 170,000 premature births globally and 172,000 stillbirths.
The conclusions come from an analysis of the care of 671 women in five British hospitals in the last ten years.
Those treated with thick thread suffered a 15% rate of intrauterine death and 28% rate of preterm birth compared with 5% and 17% for thin thread.
The findings were tested with a second group of 50 women undergoing cervical cerclage. Detailed scans and vaginal swabs showed increased inflammation and higher levels of harmful bacteria in women receiving thick thread treatment.
They are set to be tested further by a randomised trial at the University of Birmingham.
Researcher 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.
"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, like preterm birth and infection in babies.
"Women who received the thinner thread maintained normal levels of harmless Lactobacillus bacteria in the birth canal or cervix."
Fellow researcher 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."
He added: "Our current study suggests the thick multifilament thread is associated with increased risk of complications. Even after factoring in the age and overall health of the patient, this effect still existed. However there are other factors that may influence the risks, such as surgical technique."
Jane Brewin, from the charity Tommy’s, said the study should make a "safe and proven" treatment safer.
She said: "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 and success rates should improve as a result of this work."
Relationship between vaginal microbial dysbiosis, inflammation, and pregnancy outcomes in cervical cerclage. Science Translational Medicine 3 August 2016 [abstract]
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