New Study Examines Role Of Placenta Bacteria

May 22, 2014
Originally published on May 22, 2014 12:54 pm

A new study, published this week in Science Translation Medicine, tells us more about the role that bacteria may play in the health of a newborn baby.

The study found that the placenta, once thought to be sterile, is actually home to a world of bacteria that help shape the baby’s health.

Dr. Kjersti Aagaard of Baylor College of Medicine in Houston, led the study and discusses the findings with Here & Now’s Robin Young.

Interview Highlights: Dr. Kjersti Aagaard

On the reason behind studying the placenta

“There were two reasons we were interested in looking in the placenta. First of all, several years ago, we published a study in which we looked in the vaginal microbiome in women who were pregnant, and compared it to non-pregnant women. And we found that, although the vaginal microbiome was different by virtue of being pregnant, none of the microbes we were picking up in that pregnant vaginal microbiome were similar to what other groups were publishing were present in the baby’s gut when it was born. And so we were interested in specifically looking at the placenta, because other groups, such as that of Indira Mysorekar at Washington University, had shown that when they looked under a regular microscope, about a third or so of the time, they could see just gross microscopic evidence that showed them that there were bacteria present in completely normal placentas.”

On her team’s findings

“When we compared 80-some women who’d had pre-term birth to those who’d had term birth and looked at their placental microbiome, we noticed some distinctions between the women who’d delivered pre-term and the women who’d delivered term. Now, this is just an association, meaning that we observed this, but we don’t know what potentially causes it or not.”

“We observed that the bacteria that were in the placenta were actually most similar to women’s oral bacteria. But we also have some other clues that this may be real and potentially related. We’ve known for several years now that if we treat periodontal disease once it’s set in and the pregnancy is established, then we can’t impact the rate of pre-term birth. So that would suggest that perhaps these bacteria already within the placenta earlier on, before we can potentially treat the pre-term birth, and would be consistent with what we observed in this study.”

On the significance of the placental mircobiome

“We pass onto our kids, between us and their dad, about 23,000 or so genes. But these microbes infuse in about 4,000,000 genes. So we think about the scale in what makes our kids, you know, somewhat like us but so incredibly different, it has to do with probably these interactions between our DNA, our what we call epigenome, where the programmable portion of our DNA [is], and then our microbiome, and how these all fit together is going to be really, really interesting over time to learn more about.”

Guest

  • Kjersti Aagaard, OB/GYN specializing in the field of maternal-fetal medicine. She is an associate professor at Baylor College of Medicine.
Copyright 2014 WBUR-FM. To see more, visit http://www.wbur.org.

Transcript

ROBIN YOUNG, HOST:

It's HERE AND NOW. A new study out this week tells us more about the role that bacteria may play in the health of a newborn baby. The study, published in Science Translation Medicine, found that the placenta, once thought to be sterile, is actually home to a world of bacteria that help shape the fetus' future health but also may play a role in premature birth.

This raises a lot of questions about vaginal birth versus C-sections and the role of a mother's health. Take periodontal disease. Is that bacteria making its way to the placenta? DR. Kjersti Aagaard of Baylor College of Medicine and the Texas Children's Hospital in Houston is lead author on the study. She happens to be in Copenhagen at a conference and joins us by Skype. Welcome.

KJERSTI AAGAARD: Thank you, Robin, it's a pleasure to be on with you.

YOUNG: And first a primer. The placenta is...

AAGAARD: The placenta is commonly called the afterbirth, and it's the organ that supports the pregnancy and the infant as it grows, transports the nutrients and oxygen and we think regulate many aspects of pregnancy health.

YOUNG: Well, and it's just fascinated to be reminded that the placenta is the only organ that we grow and then discard. It's just quite fascinating. And it was thought to be bacteria-free. So what did you find?

AAGAARD: So we found that when we us a genetic microscope, we were able to find that there are actually many bacteria in the placenta.

YOUNG: This is part of the microbiome. We've spoken of this, the trillions of microbes, bacteria, viruses that live in the human body. And you found them in the placenta. Why were you looking, by the way, at the placenta?

AAGAARD: There were two reasons we were interested in looking in the placenta. First of all, several years ago, we published a study in which we looked at the vaginal microbiome in women who were pregnant and compared it to non-pregnant women. And we found that although the vaginal microbiome was very different by virtue of being pregnant.

None of the microbes we were picking up in that pregnant vaginal microbiome were similar to what other groups were publishing were present in the baby's gut when it was born. And so we were interested in specifically looking at the placenta because other groups, such as that of Indira Mysorekar at Washington University, had shown that when they looked under a regular microscope, about a third or so of the time they could see just gross microscopic evidence that showed them that there were bacteria present in completely normal placentas.

YOUNG: And by the way, doctors are cautioning that this is an important but preliminary study, so we'll advance with caution. But if the thinking is that bacteria in a newborn can come from the placenta, how does that relate to let's start with the question of premature birth. How might that impact the thinking about premature births?

AAGAARD: When we compared 80-some women who'd pre-term birth to those who'd had term birth and looked at their placental microbiome, we noticed some distinctions between the women who delivered pre-term and the women who delivered term. Now this is just an association, meaning that we observed this, but we don't know whether it potentially causes it or not.

YOUNG: Well for instance there's been a connection made between periodontal disease or urinary tract infections in pregnant women and an increased risk of premature birth. But questions about, well, how would that work, and in this case it may be, again may be, that bacteria from periodontal disease is going to the placenta.

AAGAARD: Absolutely, Robin. We observed that the bacteria that were in the placenta were actually most similar to women's oral bacteria. But we also have some other clues that this may be real and potentially related. We've known for several years now that if we treat periodontal disease once it's set in, and the pregnancy is established, then we can't impact the rate of pre-term birth.

So that would suggest that perhaps these bacteria already within the placenta, earlier on, before we can potentially treat the pre-term, and would be consistent with what we observed in the study.

YOUNG: In other words you might treat periodontal disease in a mother and maybe clean it up, but the bacteria is already in the placenta.

AAGAARD: Correct, and so that would get at these ideas of really being preventative in pregnancy and prevention of pre-term birth. And we like to remind women that pregnancy is an interval before you get pregnant to optimizing your health and the months afterwards, when you're breastfeeding your baby and caring it in just all the loving, day-to-day ways that women do with their children.

YOUNG: Well, that's the downside of bacteria, but what about good bacteria? There's long been thinking that a mother's birth canal transfers helpful bacteria to the baby during birth, and there's a concern that children born by C-section don't get that helpful bacteria. Does this research mean that, well, yes, they do because they might be getting it from the placenta?

AAGAARD: So that's a great question. This specific study didn't address that. What we did find was we couldn't tell a difference in the placental microbiome based on whether or not women had a vaginal or Caesarean birth. We like to think optimistically that we don't think women have really doomed their babies to a forever altered microbiome just because they had a Caesarean.

YOUNG: Meanwhile, Dr. Aagaard, just one last question because we also know you looked at diet. Given that now there is bacteria in the placenta, what that means is still some unanswered questions, but is there something that pregnant mothers should do knowing that, with what they eat or drink or their health care?

AAGAARD: So on Tuesday, we had come out in Nature Communications, our work with the Oregon National Primate Research Center, in which we looked in non-human primates at the impact of the maternal diet during gestation and lactation. We found that if the moms had a high-fat diet, specifically a 35-percent high-fat diet, that forever altered their infant's microbiome.

The high-fat diet was a negative impact, including if we then switched those babies at the time they were weaned onto a control diet.

YOUNG: So even if you change the baby's diet, the mother's diet still impacted it?

AAGAARD: Exactly. We've also shown in the same non-human primate model that there are some benefits to thinking about women changing their diet. So these monkeys over time become obese with that high-fat diet. If we change their diet right before they get pregnant back to a healthful diet, we have seen benefits to the infants by switching them back over.

And I think that's a really important message for so many women because it says while you may not be able to, nor is it potentially even safe to, lose tremendous amounts of weight in pregnancy, you can switch what you're eating, and that will have some benefit for your baby.

YOUNG: So it's the microbiome and not genetics?

AAGAARD: Yes.

YOUNG: Or maybe in addition to genetics, but it's the microbiome. That's so fascinating.

AAGAARD: Yeah, so we pass on to our kids, between us and their dad, about 23,000 or so genes. But these microbes infuse in about four million genes. So when we think about the scale and what makes our kids, you know, both somewhat like us but so incredibly different, it has to do with probably these interactions between our DNA, our what we call epigenome or the programmable portion of our DNA and then our microbiome.

And how these all fit together is going to be really, really interesting over time to learn more about.

YOUNG: Dr. Kjersti Aagaard of Baylor College of Medicine in Houston and also Texas Children's Hospital in Houston, the lead author in a new study on bacteria in a pregnant woman's placenta and also, as we just heard, on diet. Dr. Aagaard, thanks so much.

AAGAARD: Thank you, we really appreciate your interest.

YOUNG: And you are listening to HERE AND NOW. Transcript provided by NPR, Copyright NPR.

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