Radiolab – "Fetal Consequences"
Date: May 1, 2012
Hosts: Jad Abumrad & Robert Krulwich
Main Guest: Dr. Kirby Johnson (Tufts University)
Theme:
Exploring the mysterious phenomenon of fetal cells lingering in mothers' bodies for decades, and the mixed—sometimes poetic, sometimes unsettling—consequences this may have for their health.
Overview
This episode of Radiolab delves into the science and emotional resonance of “fetal microchimerism”—the surprising fact that cells from a fetus cross into the mother’s body during pregnancy and can remain there for decades, possibly even a lifetime. Hosts Jad Abumrad and Robert Krulwich revisit an early story reported by Krulwich and get an update from research scientist Dr. Kirby Johnson about what we now know, what remains uncertain, and what it all means for both science and relationships.
Key Topics and Insights
1. The Initial Science: Fetal Cells Remain for Decades
[02:58 – 04:30]
- Kirby Johnson explains that for much of medical history, it was believed the placenta formed a near-impenetrable wall between fetus and mother.
- New findings show that dozens or even hundreds of fetal cells cross into the mother’s bloodstream and tissues, persisting for decades—"40 years after conception...fetal cells are still floating around inside the mother" (Kirby Johnson, [04:08]).
- This is true even in cases of miscarriage or abortion; cells from all pregnancies linger.
2. Two Competing Hypotheses: Harmful vs. Helpful
[04:49 – 06:14]
- Hypothesis 1 (The "Bad Hypothesis"): Fetal cells contribute to autoimmune diseases (e.g., lupus, rheumatoid arthritis) that are more common in women.
- "Maybe it’s her fetal cells, her own babies taking a poke at her." (Narrator, [05:13])
- Hypothesis 2 (The "Good Hypothesis"): Fetal cells help heal and repair their mother’s tissues after injury or illness.
- "The son or daughter cells stay in mom...to protect, defend and repair her for the rest of her life..." (Narrator, [05:52])
3. Striking Case Study: Healing the Liver
[06:25 – 07:30]
- Story of a woman with hepatitis and a history of five pregnancies:
- Her liver biopsy revealed "sheets of fetal cells" at the site of liver damage, far beyond what’s typical ([07:07]).
- She recovered without intervention—prompting speculation: "Could that lead us to think...she was saved by her kids?" (Robert Krulwich, [07:41])
- Johnson responds poetically yet cautiously: "It's the most likely explanation...But it has to be right, and we can't be led astray by our own desire for it to be true." ([07:53 – 08:15])
4. Current Animal Studies and Evidence
[08:15 – 08:58]
- Animal studies show fetal cells rush to sites of disease or damage (e.g., cancer, infection).
- "There’s a lot of evidence now...that these cells may actually be repairing tissue that is protecting the mom." (Carol Artlett, [08:42])
- The "bad hypothesis" is losing traction: "I can't recall a single study that's been truly reproduced to verify the bad fetal cell hypothesis." (Kirby Johnson, [08:58])
5. A Personal and Poetic Scientific Quest
[09:34 – 10:00]
- Johnson reflects on his own mother’s illness: "If there's some way where I...contributed to the extension of my mother's life, even if it was a few days, that would make all of the years that I spent doing this research worthwhile." ([09:34])
Update: Six Years Later—Complexity Deepens
6. Progress and New Tools
[10:06 – 11:41]
- Johnson now tracks fetal cells in mice using green fluorescent protein, making them glow visibly. "It is like the movies...it is shiny, glowing green." (Kirby Johnson, [11:25])
- Fetal cells show up in many organs—even in the brain.
7. Mixed Roles: Helpers and Harmers
[11:56 – 14:07]
- Evidence shows fetal cells can help repair tissues (e.g., after liver damage), but in autoimmune cases, "their behavior seems to suggest that they are attacking the mom, actually attacking maternal tissue." (Kirby Johnson, [12:40])
- The outcome depends on numerous variables: the type of disease, location in body, the father's genetics, number of pregnancies, pregnancy losses, and maternal age.
- "It gets longer... The number of pregnancies, also pregnancy loss... maternal age, that's another very important variable." (Kirby Johnson, [14:10])
- "Good kids and bad kids. You have good days and bad days, good cells and bad cells." (Kirby Johnson, [13:58])
8. The Limits of Knowledge and the Drive for Truth
[14:32 – 18:56]
- Krulwich asks if the ambiguous, messy reality diminishes Johnson's enthusiasm.
- "Whether or not the truth is wonderful or the truth is horrible, that's what I want to find out, regardless of what the end personal outcome is." (Kirby Johnson, [17:07])
- On the value for him and his late mother: "...At least I know what the truth is. And both as a son and as a scientist, that would be of value to me." (Kirby Johnson, [17:58])
Notable Quotes & Moments
-
On the poetic wish for fetal cells to be protectors:
"[It] does touch the heartstrings of even the most hard-nosed research scientist. But it has to be right, and we can't be led astray by our own desire for it to be true."
— Kirky Johnson ([06:07], [08:15]) -
On the ambiguity of science and personal connection:
"You might even come out the villain. Doesn't that sap your enthusiasm?"
— Robert Krulwich ([16:50])"As a scientist, I want to find the truth. Whether or not the truth is wonderful or the truth is horrible, that's what I want to find out."
— Kirby Johnson ([17:07]) -
On the messiness of the findings:
"The cells can be good or bad. Depends on the disease, the location, and the dad. But we're not really sure why."
— Jad Abumrad ([14:01]) -
A Mother's Day reflection:
"I don't know that mothers really need a day. They should basically own the calendar. But since here we are chronologically near Mother's Day. Happy Mother's Day."
— Jad Abumrad ([19:03])
Timeline of Key Segments
- [02:58 – 04:30] – Discovery of fetal cells remaining in mothers for decades
- [04:49 – 06:14] – Competing hypotheses: harm vs. healing
- [06:25 – 07:30] – Case study: fetal cells in liver disease
- [08:15 – 08:58] – Animal studies and mounting evidence
- [10:06 – 11:41] – Technical update: tracking fetal cells in glowing mice
- [11:56 – 14:07] – Mixed effects: when fetal cells help or harm
- [14:32 – 18:56] – Reflections on uncertainty, science, and motive
Tone and Style
The episode mixes playful banter, earnest science, and poignant reflection. Krulwich’s probing is both charming and direct; Johnson emerges as a thoroughly human scientist, candid about both his hopes and disappointments. There is a searching tone throughout—a willingness to embrace both poetry and uncertainty in pursuit of answers.
Conclusion
"Fetal Consequences" beautifully illustrates the complexities at the intersection of biology, personal history, and scientific rigor. The story resists easy answers but offers instead a glimpse into how science advances—not toward tidy truths, but through messiness, questions, and deep personal investment.