Around 50,000 babies are born prematurely every 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. Around one in 200 pregnant women who are at risk of giving birth early have stitches put into their cervix to prevent the baby from being delivered too soon.

Premature birth may be triggered by the cervix opening too early in the pregnancy, causing the baby to start moving down the birth canal. The causes are unknown, but infection in the birth canal is thought to be a factor.

But scientists at Imperial College London discovered that the thread used in the majority of operations creates a haven for bacteria which can lead to infection and trigger a dangerous immune response which causes early delivery or still birth.They found potentially dangerous bacteria grew more easily on the thicker thread. Switching to a thinner nylon thread could prevent the deaths of around 260 babies a year and stop 280 being born early, the researchers estimated.

Professor Phillip Bennett, lead author of the study from the Department of Surgery and Cancer at Imperial, said: “Although the cervical stitch procedure still holds benefits for women overall, our results suggest the thicker thread may encourage the growth of potentially dangerous bacteria in the cervix.

The study, analysed 671 UK women at five hospitals who received a cervical stitch procedure to prevent miscarriage or premature birth.
Surgeons use one of two types of thread for the stitch – the majority use a thicker woven thread, and around 20 per cent use a thinner thread. The study, published a year ago in the journal Science Translational Medicine, suggest the thicker thread is associated with a three-fold increase in rate of baby death in the womb when compared to the thinner thread, and is associated with an increased rate of premature birth.

Dr David MacIntyre, scientific lead of the study, also from the Department of Surgery and Cancer at Imperial explained: “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 per cent 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.”

The team 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. “