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Detroit — Detroit researchers who authored a groundbreaking study on vaginal bacteria in pregnant women have raised questions about conclusions of a Stanford University study published Monday that suggests a link between the vaginal ecosystem of pregnant women and their risk of preterm delivery.

Published in Monday’s Proceedings of the National Academy of Sciences, Stanford researchers suggest doctors may one day be able to tell who’s at risk of having a premature baby by studying the microbiome — the community of micro-organisms that live in the mother’s reproductive tract.

But Drs. Roberto Romero and Sonja Hassan of the Perinatal Research Branch of the National Institutes of Health say a similar study they published in the journal Biome in February 2014 with a larger sample size did not establish such a link. Historically, more Detroit babies are born prematurely than anywhere else in the nation.

Romero and Hassan, Wayne State University researchers who work at the Detroit Medical Center, note that their study involved 90 women, with 18 who were pregnant, compared with 49 studied with 15 pregnant at Stanford. The Detroit study found no relationship between bacteria in the vagina and premature birth, and Romero said it’s premature to suggest such a link.

At Stanford, scientists found that a specific pattern of vaginal bacteria was linked to greater risk of preterm delivery, and the longer the pattern persisted, the greater the risk.

“I think our data suggest that if the microbiome plays a role in premature birth, it may be something that is long in the making,” the Stanford study’s lead author, Dr. Daniel DiGiulio, a research associate and clinical instructor in medicine, said in an article published by Stanford Medicine. “It may be that an event in the first trimester or early second trimester, or even prior to pregnancy, starts the clock ticking.”

DiGiulio said Monday variations in the two studies might explain the differing results. The women studied in Detroit were predominantly African-American, compared with a largely Hispanic-American and Asian-American group at Stanford. They found those who went into preterm labor harbored a different pattern of vaginal bacteria than the other moms-to-be.

“Previous studies have demonstrated that the vagina of non-pregnant women may vary with ethnicity,” DiGiulio said.

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Both teams of researchers collected bacterial samples from the women’s vaginas throughout pregnancy. Stanford researchers also studied bacteria from teeth, gums and stool. While both teams took samples from women at intervals throughout pregnancy, DiGiulio noted the Stanford team took samples more frequently than in Detroit.

The teams also found women who’s vaginal ecosystems are dominated by lactobacillus bacteria, a family of bugs long thought important for vaginal health. Non-pregnant women have more of this variety, due to menstruation. But the lack of these bacteria was not linked to prematurity risk, Romero said.

About 450,000 U.S. babies are born premature, before completion of the 37th week of pregnancy. That’s 11.4 percent of the babies born in 2013, a rate that has been inching down from a peak of 12.8 percent in 2006. Doctors have made strides in saving increasingly early preemies, but those babies are at greater risk of lasting vision and developmental problems.

Both scientists said more research must be done to examine the role of bacteria in premature birth.

“We published this study to let the scientific community know what we were finding,” Romero said Monday. “We will take a second look with a larger sample; it’s already underway.

“This (research) is something that has happened in Detroit; we’re way ahead of all these people.”

DiGiulio said Romero has led groundbreaking studies, including the work that established a link between bacteria in amniotic fluid and preterm birth.

“Romero did a stellar job of starting the first chapter and we are continuing that work,” DiGiulio said.

kbouffard@detroitnews.com.

The Associated Press contributed.

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