What If Pregnancy Builds A Family Archive In Your Cells

A tiny number of living cells can cross the placenta and be exchanged between mothers and babies. These exchanged cells can stay for decades, sometimes for life, turning pregnancy into a lasting biological connection you can’t see with the naked eye. That phenomenon is microchimerism, and it’s one of the most fascinating pieces of pregnancy science we’ve ever explored. 

This week we’re joined by Dr. Tara Sander Lee, a scientist with more than 25 years of experience spanning public policy, academic research, and clinical medicine. Together, we break down what fetal microchimerism and maternal microchimerism actually mean, how researchers first proved it using Y chromosome detection and fetal DNA in maternal blood, and why scientists now find these cells across many maternal tissues. Learn how modern prenatal screening relies on the reality that fetal DNA can be detected surprisingly early.

You will also discover the hopeful medical implications: fetal cells that appear to migrate toward injury sites after a C-section, reports suggesting fetal cells may contribute to maternal heart repair, and the way maternal cells can help train a baby’s immune system. We connect those insights to real-world outcomes like transplant tolerance, why maternal organ donation may sometimes be better tolerated, and what this could mean for future fetal surgery and in utero stem cell transplantation for genetic disorders.

Finally, we address the public debate this science touches, including claims that an unborn baby is a “parasite,” and why cellular evidence points to a far more complex and human story. 

Subscribe for more, share this conversation with someone who loves science and life, and leave a review with your biggest question about microchimerism.

Here are resources to discover more about this fascinating phenomenon:

Resources: 

Salt4life.org 

 Beyond the Biological Souvenir: The Evolving Landscape of Fetal Microchimerism 

 Forever Connected: The Lifelong Biological Consequences of Fetomaternal and Maternofetal Microchimerism 

 Voyage of Life: Fetal Microchimerism 

 Grandmaternal cells in cord blood 

Transcript

Microchimerism: Cells Shared In Pregnancy

Dr. Tara Sander Lee 0:03

So, what happens during pregnancies is that a small number of cells pass between mother and fetus in both directions. And so these cells, what they're finding is that they can remain in the body for years or even decades, and possibly for the person's entire life.

Victor Nieves 0:24

We've often heard mothers around the world say they feel like their children are still a part of them long after they've given birth. It turns out that's absolutely true. Mothers pass along fully formed cells that continue functioning for years within their baby's body. It's a phenomenon that the scientists call microchimerism. Fetal cells can also be found in virtually all maternal tissues, including the liver, blood, bone marrow, heart, lungs, and other tissue types after pregnancy. Scientists have also been finding that children are equally receptive to retained mother cells, with approximately one in every million cells in our body being of maternal origin. Welcome to Straight Talk on Life Issues. I'm Victor Nieves, president of Life Issues Institute. Today we have the pleasure of being joined by Dr. Tara Sander Lee. She's a scientist with over 25 years of experience in public policy, academic research, and clinical medicine in the life sciences. Dr. Tara Sander Lee, thank you so much for joining us today.

Dr. Tara Sander Lee 1:24

Thank you so much for having me.

Victor Nieves 1:26

Absolutely. Dr. Tara, this is one of the most fascinating topics that I think we have ever talked about on the show, and that's high praise because we've talked about some very, very interesting things. The first question, and this is to prove how much of a layman I am on this topic, how exactly do we pronounce microchimerism? Is that correct?

Dr. Tara Sander Lee 1:55

Microchimerism.

Victor Nieves 1:57

So you were really, really close. Pretty close, full take it. So now that we know the pronunciation, tell us what it really is, because like I said, it's very fascinating.

Dr. Tara Sander Lee 2:06

It is really fascinating. And thank you so much for inviting me. So I'm just gonna break down the word a little bit because maybe that'll help, just as people are pronouncing it themselves. So micro meaning small or minute, okay, and chimerism meaning the presence of two genetically distinct cell populations in a single organism. Okay, so this is a biological phenomenon in which a small number of genetically distinct cells become part of the body. So this is most often and commonly seen during pregnancy, which is amazing. And it happens in all pregnancies, right? This isn't just for a select few. So what happens during pregnancies is that a small number of cells pass between mother and fetus in both directions. So in the same way that cars can travel between two different cities using the same highway, cells cross the placenta and travel between mom and baby during pregnancy. And this is called bidirectional cell trafficking. And it's just, it's remarkable because then a small number of baby cells enter mom's body and a small number of mom's cells enter baby's body. And so if we're talking about the cells in the mom's body, the fetal cells, that's called fetal microchimerism. If we're talking about the small number of mom cells in the baby, that's called maternal microchimerism. And so these cells, what they're finding is that they can remain in the body for years or even decades, and possibly for the person's entire life. And so this is becoming a really hot area of research. People are trying to understand why they are there, what are they doing? And it just, it truly is beautiful because it's just showing how through pregnancy we are truly connected to our children and our parents and our grandparents. Because if we're going to get into the details, it's just remarkable how far this stretches. You know, it's not just mom and baby, but it's previous siblings, right? Older siblings then. There is gonna all be connected. So I also want to just point out that microchimerism is not just unique to pregnancy. It can also arise through twinning, blood transfusions, or even organ and stem cell transplantations.

Victor Nieves 4:08

Wow, that's fascinating, Dr. Terra. So when you tell me about this, I'm reminded there's many mothers forever have said, you know, I feel like there's a part of my baby that's always been with me that is literally true, is it not?

Dr. Tara Sander Lee 4:20

It is literally true. So it is a unique bond between a mother and her children that is beyond just what we see, right? This is at the cellular and molecular level, the DNA level. And it does, it creates this permanent connection, a lifelong bond. It is beautiful, it's complex, and we're still trying to understand it, but it is just absolutely beautiful. I mean, my husband and I suffered miscarriages. And so it's just really comforting to know that those children, even though I never met them face to face, that there's a part of them that is going to be for always and forever with me.

Victor Nieves 4:56

And it's just, it's beautiful. Absolutely. Dr. Tara, I'm curious. You know, you mentioned this is kind of an expanding field of research. There's so much yet to be known, I'm sure. But so far, what are some of the interesting findings? What do we know about this unique, you know, sharing of cells?

Dr. Tara Sander Lee 5:10

So maybe I'll focus on, yeah, what we do know. So the proof of this really came in the 1990s and and 2000s, in which there was definitive proof that these fetal cells in the maternal blood could detect them with the Y chromosome, right? So moms are only going to have two X chromosomes. So they started noticing, wow, we're actually detecting the Y chromosome from her son, you know, or previous generations in the mom. And so moms that were carrying male fetuses, that's how they first started to realize this. And that's where they found that they were actually finding that these cells could be detected in practically all organs. So the kidneys, the livers, the hearts, the thyroid, the lungs, right? So that was some of the earliest evidence. There was some also some convincing evidence that came in the early 1990s with the application of once they could start detecting

What We Know From Research

Dr. Tara Sander Lee 6:00

DNA, they were starting to find that unique fetal DNA in the mother's blood. Okay. We can maybe get into that because that gets into the all prenatal screening that is done now. That's the technique that takes advantage of that. But those are some of the first early things that we knew. We knew we could detect these cells in nearly all tissues. We knew they could detect the unique DNA to each individual, right? To that mother's children in her body, in her blood. There's just some other fascinating reports. So I don't know if, you know, I previously worked at the Charlotte Lozier Institute and we developed this incredible website, A Voyage of Life. So what they found is that male cells, which again contain the Y chromosome and are only found in males and not present in women, have been found circulating in mothers whose sons are up to 38 years old, and they have found a child's grandmother cells in his umbilical cord blood. So that's what's just remarkable, right? So we're seeing like not only are the sons, you know, as far as 38 years of old, but we're seeing just grandmother's DNA is present in the cord blood of a child that was just born, right? So this is just remarkable. So these are just really exciting facts. We know that they can detect these cells and DNA as early as six weeks gestation. It can be found in the peripheral blood in 100% of pregnancies by six weeks. We know again that really small number of cells, right? There, the estimates are that there are only about one to two fetal cells per mil of maternal blood. But because of technologies and how they'd advance, they can be detected, right? We have just incredible technologies to detect this. But if we look kind of broader, like what have we seen and how does this get us really excited about the potential for this? Early studies are showing that the baby cells can actually help provide possible healing for mom in the case of injury. So this is just one example where actually fetal cells have been found after a mother undergoes C-section, that they're finding that the fetal cells actually migrate to that site of injury and can be found at that site. And they might actually help to prepare the mother's tissue after a C-section. It's remarkable that they're finding that in the maternal heart, they're finding that there was this great article in Harvard Scientific Review earlier this year. And they reported how the fetal cells are actually like heat-seeking missiles that go to the woman's heart and might actually help if there's any injury in the maternal heart. And so what they're finding is that these early fetal cells, they actually have the ability to, they're called the pluripotent. So they have the ability to kind of change into different types of tissue cells. So they were saying how these cells don't just sit in the maternal heart, right? They actually differentiate or change into the specific type of cells that are needed in that mother's hell heart to actually help mend if there is any injury to that mother's heart. So that's just remarkable, right? But we're also seeing that it might be the reverse, too, that the mom cells might actually provide possible healing for the baby. So we're seeing the importance of maternal cells actually in educating the fetal immune system. So we know that these different cells that are passing over into the baby from the mom, that some of these cells are these immune cells that help fight off infection. And so these studies are showing that actually mom cells can help establish and train the child's immune system to fight off infection as the baby develops after birth. So these are just, you know, beautiful things. You know, we we know that the significance of maternal microchimerism for transplantation might actually be really important for curing and helping to cure and treat fetal genetic disorders. So let me kind of walk you through this. So what we're finding is that the presence of a mother cells in a baby could actually result in therapies that help to treat the fetus that have genetic disorders. So what they found is that studies have shown that there's an improved survival after a child has had a liver transplant from a maternal donor compared to a paternal donor in children with bilary atresia because it's what's happening is that the baby has already seen the mother's cells, okay, during pregnancy. So now, if that baby needs a transplant, that baby has a better tolerance for the mother than for the father, right? And so that's what's beautiful. We also see this in this amazing new ability for fetal surgery inside the womb. We know that this is really expanding, in which babies, once they discover a disorder inside the womb, there are some disorders that can actually be treated inside the womb, either with a transplantation or with actual fetal open surgery or petoscopy, right? In one example, in utero stem cell transplantation has been done in a baby. Once they realize that the baby inside the womb had a blood disorder, such as alpha thalassemia major, what they found is that they can use a mother's own stem cells

Healing, Immunity, And Future Medicine

Dr. Tara Sander Lee 10:55

to treat her baby inside the womb. And so that baby has a greater tolerance, again, because the baby has seen the mom's cells already. And now the mother's cells can actually be used to help to treat that baby and repair that blood disorder. So it really is just remarkable. So people are starting to get really excited, like, wow, what else can these cells do, right? If we already know that they're helping to repair the mom's heart, they're helping, you know, repair the C-section, you know, the mom's cells are helping the baby to better receive like a transplantation. And so it's just people are getting really excited.

Victor Nieves 11:30

Well, you can understand why. There's so much there, Dr. Tara, that I I want to unpack because really I just can't say it enough. This is so incredibly fascinating. One of the things that stood out as you're explaining this, I mean, this is real science stuff. So what stood out to me though is a little bit more elementary. And it is as you're describing the transfer of the cells and all of these potential benefits and the amazing science and the more that we're learning about it, we've already established this in much simpler science. But my goodness, how could anyone say that the baby is a part of the mother's body? That's of course not true. We're seeing, you know, these male cells in the mother's bloodstream. It just puts it all to bed. It's the more that we learn about the unborn baby in the womb, the more screamingly obvious it becomes day by day that this is clearly a unique human being in the mother's womb. One of the things, Dr. Tara, as well, that really caught my eye about this topic is I was doing some pro-life apologetics, and we hear these debates, we hear these claims from the other side. And one of them that they'll try to say to be a little bit edgy, is they'll say, well, the unborn baby is a parasite. You know, they love to say that. The unborn baby is a parasite, which is actually, like I said, it's the first time I learned about this because of the studies that say that we have seen these fetal cells traveling to the site of injury and actually healing the heart tissue or healing, you know, these different organs. And that is just one of the most incredible things. And of course, it refutes the idea that the unborn baby is a parasite. There's many ways to refute that. But I just want to park on that for just a second and kind of highlight it. The fetal cells are traveling into the mother. I loved the language you used there. You said it's like a heat-seeking missile. These cells are going and actually, we have reason to believe, healing the mother's heart tissue.

Dr. Tara Sander Lee 13:12

Yeah, that's exactly right. And I love how you just paused and said, let's just remind ourselves that human life begins at conception and this such a genetically unique individual. I want to just reiterate that that we know that when the sperm and the egg come together, the sperm and the egg each have half the amount of genetic information needed to create a complete human organism. Only when they come together that they create a unique human being that is unlike any other. And I just want to give you this statistic because I think this is fascinating, the way that God designed DNA in order to provide that uniqueness. The probability of there being two identical children from any two parents in the population is 6.27 billion to one. So we are all absolutely unique, even twins, right? Even twins, there are subtle differences. And we know that these little ones, that when their cells from the outside of the embryo, when they implant into the mother, that they help to form that placenta, that temporary organ that attaches to the unerol and will provide those nutrients and oxygen to the fetus that are needed. It's a temporary organ. And the baby is absolutely distinct and unique. And like you said, when those cells then travel to the mom, those are separate cells unique to the baby. When the cells from the mom travel to the baby, those are unique, separate cells unique to the mom. These are two completely separate human beings that are genetically unique. I'm telling you, a parasite does not have a beating heart by 22 days after conception. A parasite does not have fingers and toes. You know, by 10 weeks, 90% of the body parts are already formed in a human being. I mean, it is remarkable just the humanity of the unborn child. And it's beautiful that this connection between the baby and the mom inside the womb is unlike any other.

Victor Nieves 15:02

You know, Dr. Tara, as as you talk about what we know, I can't help myself. I have to ask the question. I we've talked about how amazing it is, the science that already exists. If you had to be speculative, if you look at the body of research and because this is relatively new, I mean, we're learning this more and more day by day. If you could fast forward 50 years, what do you think? Have we reached the crux, I suppose? Have we found out all there is to know about this topic? Or do you see there being more maybe medical breakthroughs and innovation as we learn more about it?

Dr. Tara Sander Lee 15:32

I think there are going to be a lot of medical breakthroughs. I think now that technology is at the point where you can detect these cells and the DNA in such small amounts. And now that they know what to look for, I think we are going to see a lot of really fascinating discoveries. If I had to fast forward, I think what we're going to see is that this ability that God designed for a mother and a child to connect in this very, very molecular, like that's the best way I can say, cellular and molecular way. I know that's a very scientific way, but it's basically a way that we can't see with the naked eye. But now these tools have been developed. I think we're going to see that this is a way that not only we know that stem cells within our own body can help to heal us, but I don't think we're going to see that stem cells that are exchanged between mom and baby are going to be a whole another layer by which our body is healed. It's a gift. I think we are constantly reminded in scripture how much children are a gift from God. And I think what we're going to find is that these are gifts that the mother gives the child and that the child gives the mother once they are separated. They are gifts that are long-lasting and stay with the child forever. That's what I think we're going to see. I know that there are some researchers that are trying to say, yeah, but could this also be a bad thing, right? Could somehow that offspring's demand, you know, that baby's demand for the resources of the mother, could that somehow cost it, come at a cost of the mother? And could these cells that the baby transfers into the mother somehow cause problems and actually lead to disease? People are definitely raising those questions. I mean, no different than people are starting to say, you know, you know, saying that they're just calling the human being a parasite. So I think we need to watch this field very closely. I think there are going to always be individuals and researchers and scientists that are not going to see pregnancy as the real gift that it is, and that there is a gift of grace in pregnancy. And we already know there's healing that's happening between the two in sharing of these cells. But there are people that are trying to say, but couldn't this result in bad things? Right? So we need to keep our eyes and ears open because the reality is pregnancy is beautiful and it's a beautiful gift. And it's another human being that was created in the likeness of God for a purpose. And that human being always needs to be seen with the dignity that they deserve and the value that they deserve, that they are created in the likeness of God. And we don't understand everything there is to know about disease, but I think if I had to fast forward, I think we're gonna see that these cells have tremendous healing power. And I just want to pause really quickly and remind the audience that stem cells that derive from the fetus are known to have healing power. You know, the cord blood is the baby's blood that's left in the placenta after the baby is born and after the umbilical cord is cut. And we know that cord blood is a rich source of stem cells that can heal and be used for life-saving stem cell transplantation. Cord blood comes from the fetus, right? As you remember earlier, those cells from the fetus actually help to form the placenta and that umbilical cord. And so we know that these cells are already being used to treat thousands

Unborn Life, Ethics, And Public Debate

Dr. Tara Sander Lee 18:55

of diseases in our nation and worldwide and treat many different cancers, immune deficiencies, and genetic disorders. So we already know that these. So if anybody is tempted to say, well, could fetal cells actually harm? I'm going to point to everything that shows that they only heal. They've only been shown to be a powerful source of healing. That's what I would say if anybody asked me.

Victor Nieves 19:15

Well, and Dr. Tara, to your point there, you know, we hear this, and I think most people who are willing to look at this with an open mind are very excited. This is incredible information. This is fascinating information. It says a lot, I would say, about the way that these people view the world. When you hear this amazing news and you have to find a bad thing, you have to find some reason. Well, this might actually be bad for the mother. Now, I'm not saying it's not healthy to have dissenting opinions or to have people who are thinking about maybe the unintended consequences. That's healthy and that's good. I think that this extends beyond that, though. I think this shows that those in the abortion industry, this has become something of a religion for them. And they simply cannot allow it. So when the science comes out that says, hey, the unborn baby is sending repairing cells to the mother, what an amazing thing. Look at the blessing of this child. They can't allow that. There has to be a downside. There has to be some sort of a negative. They don't want to live in a world where the unborn baby is beneficial to the mother, or where the unborn baby, you know, carries its weight in some sort of a way because they have to paint this image as though a child is nothing but a burden. A child is this awful disease. You know, they act like pregnancy is some sort of a disease, and the cure is to kill an innocent child. And so it's disheartening. Of course, we know that this is going to happen, but it's disheartening whenever we see something that should be so encouraging. And I like the vision you have for the future. I think it's very well grounded based on all of the research that we have right now. This looks to be a wonderful blessing. And, you know, to be able to find fault in something as beautiful as an unborn baby sending their cells to repair a mother's heart, that's one of the most pure things I've ever heard in my life, is that a baby is sending, you know, cells to help heal the mother. To find something off with that, I think it says, I think it says a lot about the state of mind of those who are in opposition to life. Dr. Tara, I'm curious. I think you had mentioned earlier this microchimerism, it can have a relationship with siblings. Did I get that correct? So does this apply to twins?

Dr. Tara Sander Lee 21:13

So it does. So what's remarkable is that not only twins, but siblings, older siblings and younger siblings. So, okay, let's say the mother is pregnant with twins, okay? We know that you can have microchimerism between twins in some cases and twinning. So they're sharing there, but then both of those babies inside the womb are going to share their cells with their mom, and the mom is going to share their cells with those twins. But what's also remarkable is that sometimes cells from an older sibling may even be passed to a younger one, right? Because mom now, let's say she has three children, okay? Her first child, her oldest, that baby shared the cells with the mom. The mom then got pregnant with baby number two. So now the cells that were already in mom, that oldest sibling, now are going to pass with the mother cells to the new child, right? And so it just kind of that's what's so remarkable. And like I mentioned, like a child's grandmother cells have been found in the umbilical cord. I mean, so we just see this cross-generational ability of these cells within a family to just be shared and to be connected. You know, we have a son, and like I said, we had many miscarriages, but it's like how comforting even for a sibling to know if they lost another sibling that there actually might be a connection there.

Siblings, Faith, And Closing Resources

Victor Nieves 22:35

Well, it could literally be a piece of them with you for your entire life. Talk about heartwarming. I mean, that's wow.

Dr. Tara Sander Lee 22:40

It is so heartwarming. And so I think, you know, I want to remind the audience of what it says in Psalm 139. When King David wrote these words, you know, was inspired by the Holy Spirit years ago. You know, science has just completely reminds us and validates just the beauty of being formed in the womb. And now we know actually sharing in that healing between us, right? So for you created my inmost being, you knit me together in my mother's womb. I praise you because I'm fearfully and wonderfully made. And then the psalmist reminds us in 139, your eyes saw my unformed body, and all the days ordained for me were written in a book before one of them came to be. So, you know, God is in complete control of all of this. And he is a God of grace and of mercy and of healing. He's the great healer. These children are already a gift. Why wouldn't there be a gift that continues even beyond pregnancy, right? I mean, I was pregnant myself, and yes, you know, you're you maybe have some sleepless nights, but it is beautiful. It is beautiful. And to have that gift continue then beyond even the pregnancy in even ways that we can't even fathom or see is absolutely beautiful and just a gift of grace.

Victor Nieves 23:52

Well, Dr. Tara, thank you so much for joining. I think that is the perfect note for us to end it on. This has been so incredibly just encouraging to me, but oh my goodness, it's been so informative. Thank you for joining us.

Dr. Tara Sander Lee 24:03

Thank you so much for having me.

Victor Nieves 24:15

Well, like we said at the beginning of the show, and as you can clearly see now, this is one of the most fascinating topics I think we've ever had the pleasure of discussing on the show. I love the way Dr. Tara explained very complicated scientific truth, but a very interesting, a very encouraging future that may well come as a result of fetal microchimerism and all of the details, the undeniable truth as we learn more and more about the baby in the womb. This is clearly not a piece of the mother's body. This is a distinct human being, a distinct human organism. And to think that it is literally sharing, quite possibly, fetal stem cells to go and heal the very heart of his or her mother, I just think that's one of the most incredible and beautiful things that we have ever talked about on the show. If you'd like to learn more about this fascinating topic, visit our website, lifeissues.org. We'll have more information, research, and studies so that you can share this with your friends and your family as together we fight to defend life. Be sure to tune in next week for another straight talk on life issues.