Cervical stitching is used to reinforce the cervix in women at risk of giving birth prematurely.

Cervical stitching is used to reinforce the cervix in women at risk of giving birth prematurely.

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Common technique to prevent premature birth could actually cause it

For more than a century, surgeons have stitched up the cervices of women at risk of premature birth or miscarriage to prevent this passageway from opening up too early. But a new study suggests that the suture material most often used for these procedures could disrupt the community of bacteria in a woman’s vagina and actually increase the possibility of complications.  

The most common cervical stitch involves sewing up the base of the cervix like a coin purse early in the pregnancy and then removing the stitches in the last few weeks. There are no specific guidelines on what kind of suture material is best to use, says study co-author Phillip Bennett, an obstetrics researcher at Imperial College London. For decades, surgeons have preferred braided polyester sutures because of their perceived strength and ease of use compared with thinner nylon monofilament sutures. However, recent research has shown that the multiple fibers of these braided sutures cause them to absorb fluids and harbor bacteria, thus increasing the risk of infection. “Bacteria are able to lay down a sort of matrix on the stitch,” Bennett says, “and that matrix then forms a good substrate for them to grow on.”

To find out what impact all of this might have on the risks of cervical stitching, Bennett and colleagues looked at nearly 700 cases of women in the United Kingdom who had the procedure—also known as cervical cerclage—over the past decade. They found that 28% of those receiving braided sutures gave birth prematurely, versus 17% who got the single-fiber sutures. Furthermore, 15% of women with braided sutures had a miscarriage or stillbirth compared with 5% of those who received the nylon sutures, the team reports today in Science Translational Medicine.

The researchers then conducted their own randomized trial on 49 women receiving cervical stitches to look more closely at each suture type’s effects on the vaginal microbiome, the array of bacteria naturally found in a woman’s vagina. In a healthy pregnant woman, the vaginal microbiome is rich with bacteria of the genus Lactobacillus, which suppress invading bacteria with antibiotics and a strong acid. If that Lactobacillus population is somehow disrupted, foreign bacteria can colonize the vagina and cause inflammation in the cervix that can trigger premature birth, Bennett says. In the trial, 37% of the women receiving braided sutures had an increase in foreign bacteria growing in their vaginas, compared with none of the women receiving the nylon sutures. Still, in this small group of women, the researchers found no significant differences in miscarriage rates between the two suture materials. The small size of this trial, however, makes it difficult to draw conclusions, Bennett says.

Braided sutures (top) are composed of multiple polyester fibers woven together, whereas monofilament sutures (below) are a single nylon fiber.

Braided sutures (top) are composed of multiple polyester fibers woven together, whereas monofilament sutures (below) are a single nylon fiber.

Imperial College London

Bennett and his colleagues are now studying what comprises a healthy vaginal microbiome. Eventually, this could lead to therapies, like probiotics, that could change the vaginal microbiome to reduce a woman's risk of birth complications, he says. "The few studies there have been on probiotic therapy have not been terribly encouraging, but I think that's because we need to know more about how the community of bacteria in the vagina works."

Clinical obstetrics researcher Andrew Shennan of King's College London agrees with that need for more research of cervical stitching and the vaginal microbiome. But he worries that the possibly "spurious" findings of this study will lead to hasty changes in suture material without fully understanding the risks involved. Particularly, he takes issue with the "extraordinary" rates of preterm and birth complications in Bennett’s study—much higher than the average numbers seen in previous cerclage studies that mostly used braided sutures. A 2011 study comparing different cervical stitching techniques, for example, found that just 7% of women experienced miscarriage or stillbirth using mostly braided sutures, he notes.

"My worry is people will rush to move away from one [suture material] when the other may also have problems," Shennan says. The thinness of the single-fiber nylon sutures can make them more difficult to work with, he notes, causing them to come undone before it is time for them to be removed.

Vincenzo Berghella, an obstetrics researcher at Thomas Jefferson University in Philadelphia, Pennsylvania, is also not convinced that braided sutures are riskier. He points out that in the study's randomized trial, four women receiving the nylon sutures had premature births, whereas none with the braided sutures had any, suggesting that the braided sutures still appear to be more effective at preventing premature births. "I'm not sure that I can completely buy that one is better than the other," he says.