The procedure, called a cervical stitch, is performed on roughly 2 million women a year worldwide who are considered at high risk of miscarriage or premature birth. To delay labor, doctors place a stitch in the cervix to keep it closed.
But researchers found the most commonly used suture -- a braided thread -- was associated with tripled odds of stillbirth compared to a single-strand suture. And risk of preterm birth was nearly doubled.
"We don't have very good tools for determining who would and who would not benefit from that operation, and probably put cervical stitches in many women who don't really need them, so it's important that we first do no harm," said researcher Dr. Phillip Bennett, a professor of obstetrics and gynecology at Imperial College London.
Bennett said about 80 percent of doctors who do the procedure use the braided, tape-like material. Just one in five uses a simple nylon thread that's like a fishing line.
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"We found that women who had the braided tape material had significantly poorer outcomes than the women who had the nylon," he said.
These women were more likely to have harmful bacteria grow in the vagina, Bennett said. This was associated with inflammation and changes to the cervix.
"We didn't see any of those changes when we used the nylon stitch," he said. "We think the tape stitch allows bad bacteria to grow in the vagina and that then affects the cervix through activation of inflammation," he added.
Among nearly 700 women who had the procedure, 15 percent who got the braided "shoe lace" stitch had a stillbirth, compared with 5 percent of those who had the nylon suture. In addition, 27 percent of women who received the braided tape gave birth prematurely, compared with 17 percent of women who got the nylon stitch, Bennett said.
Bennett said that as a result of this study, a head-to-head comparison is now being done in the U.K. Results are expected in a couple of years.
"At the moment the great majority of doctors use the braided tape material, and I would say that until the results of that study become available, the material of choice should be the nylon and not the tape," he said.
For the study, Bennett and his colleagues collected data on the procedure, also called cervical cerclage, from five English hospitals between 2003 and 2013.
They also randomly assigned 49 pregnant women at risk for preterm labor to receive either the braided Mersilene or single-filament Ethilon stitch.
"The results suggested that women who received the thicker thread had increased inflammation around the cervix," said co-author David MacIntyre, a lecturer in reproductive systems medicine at Imperial College London.
"There was also increased blood flow, which is associated with the cervix opening before labor," he said. "Crucially, we also found that women who received the thicker thread had more potentially harmful bacteria in the vagina and around the cervix."
This study confirms what has been long suspected, said Dr. James Ducey, director of maternal-fetal medicine at Staten Island University Hospital in New York City.
"We know from experiments in animals that the braided sutures cause more inflammation, and many of us have advocated for years using monofilament sutures for this procedure," he said.
The one drawback is that the monofilament material is harder to work with, Ducey said.
The braided suture is used most in the United States, he said. "It's easier to tie. It stays better, gets better purchase [hold] on the tissue," Ducey said.
He believes, however, that doctors should use the single nylon thread instead. "It's going to give you a better long-term result," Ducey added.
The report was published Aug. 3 in the journal Science Translational Medicine.
More information
For more on preterm delivery, visit the March of Dimes.
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