Stitches commonly used to sew up a pregnant woman’s cervix and prevent early labor can backfire — dramatically increasing her risk of premature labor and pregnancy loss.

A specific type of thick, braided suture frequently used to stitch up the cervix can breed bacteria that seem to disrupt the vaginal microbiome and spur early labor, according to a study published Wednesday in Science Translational Medicine. Women who got those sutures were at three times the risk of pregnancy loss, and twice the risk of preterm labor, than those who got another type of suture, which is thinner and flatter.

“The braided suture acts as a good home for the bad bacteria,” said Dr. Phillip Bennett, an obstetrician-gynecologist at Imperial College London and an author on the new paper. “Those bacteria activate inflammation in the cervix, and ultimately, it opens up.”

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More than 2 million women worldwide have the stitches each year, in a procedure called cervical cerclage.

Two standard types of sutures are used: the braided suture, which is nearly as thick as a strip of tape, and a thinner, monofilament suture. There isn’t any scientific research on which of the two types is safer or more effective, but about 80 percent of surgeons prefer the braided type, the paper’s authors say.

“I’ve been classically trained with braided suture. I’ve never used monofilament suture,” said Dr. Shannon Clark, an obstetrician-gynecologist at the University of Texas Medical Branch who wasn’t affiliated with the study.

The monofilament sutures are smooth, meaning it’s difficult for bacteria to grow on them. They’re made of the same material used in intrauterine devices, which can safely be placed in a cervix for three to five years. But the braided suture doesn’t seem to be so safe.

The bacteria seemingly disrupt the vaginal microbiome, causing inflammation. Inflammation in the cervix is normal during birth — it’s a marker that it’s time for a woman to begin labor. But if the cervix becomes inflamed earlier in a pregnancy, it tricks the body into thinking it’s time to give birth.

The study included two parts: a retrospective look at 678 women who received cervical cerclage and a small, controlled study of 49 women who received one of the two sutures. More robust data is needed to nail down the specific effects of each type of suture.

“This is opening the doors to some much-needed research,” Clark said, noting that a larger trial is needed to firmly establish the connection. The same team of researchers is currently conducting a randomized, prospective clinical trial underway in the UK, though it still has several years left before completion.

In the meantime, Bennett said, the preliminary findings should give doctors pause before using a braided suture in cervical cerclage.

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