Study Shows Periodontal Disease Can Affect Newborn’s Health

Once believed to be a sterile part of the uterine environment, the placenta actually contains a multitude of bacteria that may impact pregnancy and influence an infant’s health via the bacterial structure of the gut, according to the results of a new study.

This research is one part of a wider scientific attempt to investigate the microbiome, which consists of trillions of viruses, bacteria and fungi that are part of the body.  The human microbiome plays a critical role in digestion and metabolism, and may also play a role in obesity, diabetes and many other conditions.

Researcher think that having the wrong bacteria in the placenta, or not having the right bacteria, may contribute to premature birth.  Research is still preliminary, but it is thought that this could explain why women with periodontal disease, urinary tract infections and other infections during pregnancy have increased risk of premature delivery.  This link suggests that more studies are needed into the use of antibiotics during pregnancy.

This study indicates that normal gut bacteria in infants may come from the placenta.  If confirmed, this is good news for women who undergo cesarean sections, as it was previously believed that infant gut bacteria came from exposure to bacteria in the birth canal.  “I think women can be reassured that they have not doomed their infant’s microbiome for the rest of its life,” said Dr. Kjersti Aagaard, author of the study published in Science Translational Medicine. Further studies are needed into the effects of surgical birth on the infant microbiome.

Studies have already been done on bacteria in the mouth, skin, intestines and vagina, but until now little attention has been paid to the placenta.  The fetal life support system, the placenta supplies nutrients and oxygen to the developing baby, while removing waste and secreting hormones.

“People are intrigued by the role of the placenta,” said Dr. Aagaard, an associate professor of obstetrics and gynecology at the Baylor College of Medicine and Texas Children’s Hospital in Houston. “There’s no other time in life that we acquire a totally new organ. And then we get rid of it.”

Dr. Aagaard started to wonder about the placenta when they realized that the microbes most prevalent in the birth canal did not match the population found in the intestines of newborns.  It was assumed that bacterial makeup would be similar in babies born vaginally, as they were thought to acquire bacteria during the birth process.

“It didn’t make a whole lot of sense to us,” she said. “It’s not like babies are hanging out in the vagina. They come shooting out pretty fast.” She added that vernix, the waxy coating babies are born with, may help prevent baby from picking up the bacteria.

The researchers wondered whether some of the intestinal bacteria could begin to populate the infant’s intestines prior to birth.

The researchers examined the placentas from 320 women, mostly black and Hispanic, who had vaginal deliveries at term, though some had cesareans and some of the deliveries were premature.

The scientists removed the outermost layer of each placenta and tested samples from the inside for bacterial DNA.

“The placenta is not teeming with bacteria, but we can find them, and we can find them without looking too hard,” Dr. Aagaard said.

They found that the placentas were about 90% placental tissue and 10% bacteria, similar to the bacterial density of the eye or the deeper layers of skin, but significantly different from the intestine, in which those numbers are reversed.

About 300 different kinds of bacteria were found, most of them benign.  The team found that the bacterial makeup of the placenta most closely match the bacteria found in the babies’ mouths.  As it turns out, at birth the bacteria in the mouth is very similar to what is found in the babies’ intestines.

Dr. David A. Relman, a microbiome expert at Stanford, said that his lab has also found bacterial DNA in the amniotic fluid that appears to come directly from the mother’s mouth, gut and vagina.

Dr. Aagaard theorized that bacteria from the mother’s mouth gets into the bloodstream where it then travels to the placenta, where it settles and eventually makes its way to the fetus.  While this is simply one theory, it is supported by animal research.  Oral bacteria injected into veins in mice were later found in the placenta.

This theory is supported by the long-standing observation that women with periodontal disease are more likely to have premature babies or babies with low birth weight, and treating the disease during pregnancy does not seem to mitigate the risk.  Preventing the disease or treating it before pregnancy are much more effective.

This particular study did not offer any evidence about periodontal disease because only one of the participants had it.

Women who had urinary tract infections during early pregnancy, even when the infections were treated, the bacteria was still found in the placenta and increased the incidence of premature birth.

Researchers also found that the bacterial makeup of women who delivered at term differed from those who delivered early.  Dr. Aagard said it was unclear whether the bacteria actually contributed to prematurity, or whether bacterial makeup normally changes over the course of pregnancy.

Dr. Martin J. Blaser, director of the human microbiome program at NYU Langone Medical Center, and the author of the book, “Missing Microbes,” said that Dr. Aagaard’s study was important, but argues that it is preliminary, and does not provide information useful for treating pregnant women.

“I’m intrigued by the findings about the mouth and also the relationship with preterm labor, which is a really important clinical question,” Dr. Blaser said. “Will this be a productive lead, or will it fizzle out? Time will tell us.”

He argued that pregnant women are frequently given antibiotics for a variety of reasons.  Doctors once thought that antibiotics wouldn’t affect the growing fetus because the placenta was thought to be sterile.  If the placenta is not sterile, but is instead a pathway for bacteria to travel from mother to baby, what affect to antibiotics have on the baby?