Fertility Cliff

After 35, does fertility tank? As she -- and her friends — approached the age of 35, senior correspondent Molly Webster kept hearing a phrase over and over: “fertility cliff.” It was a short-hand term to describe what she was told would happen to her fertility after she turned 35 — that is, it would drop off. Suddenly, sharply, dramatically. And this was well before she was supposed to hit menopause. Intrigued, Molly decided to look into it — what was the truth behind this so-called cliff, and when, if so, would she topple? This story first premiered in “Thirty Something,” a 2018 Radiolab live show that was part of, Gonads, (https://radiolab.org/series/radiolab-presents-gonads)a six-episode audio and live event series all about reproduction and the parts of us that make more of us. The live event was produced by Rachael Cusick and edited by Pat Walters. Special thanks to epidemiologist Lauren Wise, at Boston University. Plus, Emily, Chloe, and Bianca. And of course, Jad Abumrad. If you’re more of a visual person, here are the graphs we explain in the episode, we also include links to the corresponding papers in our Episode Citations Section, below! LINK TO GRAPHS: https://media.wnyc.org/i/1860/1046/c/80/2025/12/FERTILITY_AGE_GRAPHS_1-4.jpg EPISODE CREDITS: Reported by - Molly Webster Produced by - Arianne Wack Fact-checking by - Diane A. Kelly EPISODE CITATIONS: Audio: Gonads (https://radiolab.org/series/radiolab-presents-gonads/) A six-part audio series on reproduction and the parts of us that make more of us The Menopause Mystery (https://radiolab.org/podcast/the-menopause-mystery) One of Radiolab’s most listened-to episodes of 2025! Videos: “Radiolab Presents: Thirty Something” https://youtu.be/LOJVAaSwags?si=czCBraHf1JEqmAQi Research Articles: Graph 1: Can assisted reproduction technology compensate for the natural decline in fertility with age? A model assessment (https://zpr.io/ft6dqdbkJnTd) Graph 2: Ovarian aging: mechanisms and clinical consequences (https://zpr.io/GrPLebynpvxV) , Brookmans, et al. BUT, the graph was borrowed and actually comes from this 1991 paper, Delaying childbearing: effect of age on fecundity and outcome of pregnancy” (https://zpr.io/whWg2UAZsb6h) Graph 3 and 4: Age and fecundability in a North American preconception cohort study, (https://zpr.io/Rmqry4Kd67hY) Wise et al; Dutch fertility research Further reading: Predicting Fertility, (https://zpr.io/YEdfiYT29rUh): Magazine article on Lauren Wise’s research, Sign up for our newsletter!! It includes short essays, recommendations, and details about other ways to interact with the show. Signup (https://radiolab.org/newsletter)! Radiolab is supported by listeners like you. Support Radiolab by becoming a member of The Lab (https://members.radiolab.org/) today. Follow our show on Instagram, Twitter and Facebook @radiolab, and share your thoughts with us by emailing [email protected]. Leadership support for Radiolab’s science programming is provided by the Simons Foundation and the John Templeton Foundation. Foundational support for Radiolab was provided by the Alfred P. Sloan Foundation.

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  Hey, it's Molly.

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  And Latif, and this is Radiolab's last episode of the year.

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  Woohoo.

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  Molly, rapid fire, what was your favorite episode that you did not work on this year?

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  Voice, Annie McEwen, Matt Kilty, On The Mic, those two, they should get their own show, but I don't want them to because I want them to stay here.

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  You, go.

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  Uh, ba ba ba. I think it was, it had to be probably Lulu's profile of that quantum physicist, Qasim, in Palestine.

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  In Palestine, yeah.

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  And just because you, you feel it, you're right there with him, waiting in line for bread, or whatever it is, and all he's thinking about is quantum physics.

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  Hmm.

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  And you're just like, what? It's just a kind of a portal into a man's mind that you never would have gotten any other way.

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  Yeah, that was amazing because it's like Lulu, you know, wasn't in Palestine, but being on the phone, it was like, there was so much sound to hear of like-

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  You felt like you were there, you felt like you were right there.

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  Yeah, and I think the thing is like, especially this year,

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  Hmm.

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  Thank you, seriously, thank you.

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  Yeah, giving us the year we've had. I mean, because, Latif, it's been a hard year, right?

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  Right, because earlier this year, Congress eliminated all federal funding for public media, and our home station, WNYC, we lost $3 million in regular dependable annual funding.

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  Yeah, yeah, yeah. One of my favorites of the year. The one about the Lulu calls them hot worms, but they're really a bacteria. It just like had this magical extremophile property where it could plug into this whole other process to read DNA and it like completely revolutionized all kinds of different fields.

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  And so to round out the year, you know, we look back at all our most listened to episodes and the number one most listened to Radiolab episode of 2025, thank you for that keyboard drum roll, was our menopause episode, which Molly hosted and which our contributing reporter Heather Radke brought the story to us. And it was so good and we figured maybe, maybe people want to hear more.

• 3:56Speaker 01

  Honestly, I think they do because we heard back from so many people about this episode that we decided, okay, we can give you more reporting on this topic. And in fact, I did a story about the moments leading up to menopause and this thing that my friends and I kept hearing about called the fertility cliff.

• 4:17Speaker 03

  That sounds very dramatic.

• 4:20Speaker 01

  It was so dramatic. It was so dramatic that I decided, OK, I'm gonna dig into this. I want to understand what this phrase is and like what it actually means. And we did this story for the first time as part of a live event in 2018. And so I'm just gonna play part of that live event for you here. And then we're gonna have updates at the end. So here we go.

• 4:48Speaker 04

  Hello, hello. How's everybody doing?

• 4:52Speaker 04

  All right. Well, I'm so, we're so excited that you guys are here tonight. My name is Jad. I host Radiolab and More Perfect. And I will now introduce a rising star at Radiolab and in podcasting and at WNYC and on Planet Earth. Welcome, Molly Webster.

• 5:24Speaker 01

  Planet Earth might have been a bit bold, I will just say. Um, thank you for coming. This is amazing. Hi, everyone. OK, so why are we all here? When I started reporting on the series, one of the first things I did was I just jumped on the phone with a lot of people. People like everyone in this room. I was like trying to hit like different age groups. I wanted 18-year-olds. I wanted like 80-year-olds. I was calling all my friends back in the Midwest like, hey, I haven't visited in a while, but if you could just tell me your thoughts on reproduction, like what's it like in the Midwest? And then I was very, you know, I was like, oh, someone's, you know, 20 and married in Colorado? Yes, I'll call you too.

• 6:06Speaker 01

  And I was basically just calling and saying, when I say the word reproduction, like, what do you do? Like, what do you think? Are you like, oh, God? Or, uh, you know, interested, not interested, babies, anything more than babies? One guy talked to me about hip-hop. And I was like, I could go that way, probably won't. And, um, so there were a lot of like very random conversations. And one of the things that came up in those conversations, um, was a number.

• 6:33Speaker 01

  The number was 35. It took me a while to sort of notice the pattern. But I realized that everyone was bringing it up in different ways. It was like, "Oh, I don't know, there's not that much time left." Or, you know, women would be like, "I'm drying up. My biological clock, it's ticking." There was this idea that just kept coming up over and over again. The idea that at the age of 35, your fertility vanishes if you're a woman. It just goes up in smoke. Like, in every relationship that I'm in, I feel like it's like this countdown clock in the back of my mind, you know? And so, I feel like I experience time differently. And Bianca, the young woman on the phone here, she wasn't the only one who told

• 7:18Speaker 01

  us about this feeling. It came up in another conversation that we had with this woman named Chloe. She said she really, really wanted to have kids. She was in a relationship. She really, she and her partner got along great. Partner wasn't sure she wanted to have kids. And so, on her 30th birthday, Chloe's dad sent her an email where he basically said, like, "Get on it." "The biological clock keeps ticking, especially if you want to have several kids. You don't want to split up with your partner because they've done nothing wrong, but the biological clock..." Dot, dot, dot. Thanks, Dad. It's very helpful on my birthday. And to add flame to the fire, I talked to another woman who saw 35 as such a deadline. She decided that she was going to have a kid by herself when she was 34. She wasn't going to wait.

• 8:02Speaker 01

  And she told me that the doctors categorized her in a way that really surprised her.

• 8:06Speaker 02

  The minute you're 35, you're considered a geriatric mother. It's a condition that is written on, it was written on my birth chart because I was due two weeks after turning 35.

• 8:18Speaker 01

  And so, I kept thinking, as I was like, hearing all the stuff, I was like, "I'm not freaking out about this stuff." But like, should I be freaking out about this stuff? And then, last October, I was on the phone with this sort of big wig doctor in St. Louis. And the minute we got on the phone, the first thing he asked me was how old I was. I said I was 34. And he said, "You need to get on a plane and fly out here, and we need to freeze those eggs." And then I thought, "Bleep off." And then I thought, "Maybe when the series is done." And then I thought, you know, "Maybe I should be taking this all a little bit more seriously and actually look into this whole, like, reproductive cliff thing."

• 8:59Speaker 01

  So, started reading a lot of scientific articles, watching YouTube, and I pretty quickly found what seemed to be the culprit of the cliff. So the x-axis is age. Okay, so I need you to put on sort of your visualization cap, because we're gonna go through a few graphs in this story. And for this one, it is a line graph. It goes 20 to 45. And the y, the vertical line, is something called fecundability, which is the chance a couple will get pregnant after one month of trying. And this is what the graph looked like. The shape of the graph is a line that goes pretty straight up from puberty.

• 9:44Speaker 01

  It stays flat until the age of 33, and then it turns and goes pretty steeply down until it hits zero. Here's me describing it onstage as an animation of it unfolded. It goes, "Luuuuu."

• 10:03Speaker 01

  And then there's like a fireball at the end. So this is from a journal called Human Reproduction. It was published in 2004, and that is a cliff, if I've ever seen one. And I think another thing that I wanted to note is that on this graph, 33 is the age where you actually should start freaking out. 35, you're already done.

• 10:30Speaker 01

  But, one tiny caveat, and that is that the data behind this graph is crap.

• 10:39Speaker 01

  Yeah, this data is based on French peasants from the 1700s. And you may ask, "Why them, out of everybody?" And the idea is, is that when they're doing fertility studies, they want, ideally, they say, populations of humans that have never used birth control. So people that are like pure from artificial hormones. And their idea was that these French peasants were the way to go. And so this came up, you might have seen this. It got written about in like a lot of different magazines. And it was the data being used to terrify women. And then, so I just say, you know what, like, I reject this cliff. Because I'm done with it.

• 11:22Speaker 01

  And so at this point, I thought, maybe I should stop watching YouTube and actually, like, call someone on the phone. And so I called an epidemiologist from Boston. Her name is Lauren Weiss, and she studies fertility.

• 11:34Speaker 05

  I know where the cliff came from. There was a very pivotal...

• 11:38Speaker 01

  You do?

• 11:39Speaker 05

  Oh, yeah.

• 11:40Speaker 01

  Oh, my God. Tell me about the cliff.

• 11:42Speaker 05

  So the cliff, I'm pretty sure, came from this review paper written by Brochman's.

• 11:47Speaker 01

  Who is this Brochman guy? And why does he get to draw a cliff on my fertility?

• 11:51Speaker 05

  He's a very famous reproductive endocrinologist.

• 11:55Speaker 01

  So after we got off the call, Lauren sent me the paper she was thinking about. This one is a study of recent people, and it has the same, like, axes. It's 20 to 40 is age on the bottom, and then on the side is your chance of pregnancy. And it goes... And so this line graph, it starts high, and as it moves right, it continues just flat and unchanging. And then at some point, that line turns downward, and it arcs to the bottom of the graph, kind of like a skateboard ramp. And then it's like a little, like, a water slide at the end. And I thought, oh, that looks like, it's kind of like a mesa.

• 12:38Speaker 01

  That's like a version of a cliff. And so then I thought, well, you know, maybe this graph, I'm reacting pretty emotionally to it. So I was like, OK. This one... And so what you see on stage is, I highlight that the downward turn on the graph happens at the age of 31. 31, my friends. We should have had this event four years ago. Sigh. But Lauren says it's not really based on great data either. Is it based on more peasants? No. I'm glad you asked. It is based on recent people, but it's all people that were at fertility clinics for

• 13:22Speaker 01

  fertility issues. So one could say it's a bit of a compromised data set. It's not really representative of everyone. So, back to where we started, begs the question, what happens if you actually look at an entire population, or like, a good cross-section of the population? And Lauren, the scientist who I was talking to, did actually do that. So in 2007, she launched a study with almost 3,000 Danish women who were trying to get pregnant.

• 13:51Speaker 05

  We follow them forward in time for 12 months, or until they get pregnant, whichever comes first.

• 13:57Speaker 01

  And when you look at their data, this is what you see. So this graph looks basically like a gently sloped hill. The line starts halfway up. It goes up, actually, a little bit more. And then it curves gently down, arcing to the bottom. Ooh, oh, oh, whoa, there we go. There with that. Fertility doesn't look like a cliff at all. I feel good about that. Does anybody else? All right. Um, so on this one, your fertility goes up for a little while.

• 14:39Speaker 01

  30. It goes up till you're 30. And then, when you're 35, you're actually just below the fertility you had when you were 20, which seems like, that's, that seems great.

• 14:52Speaker 01

  So I thought, all right, I'm reacting very emotionally. Tell me some numbers. And so they said for 20 to 24-year-olds, after one year of trying and having regular sex, which is actually like a technical term, so take that as you will, but I won't judge you, the chance of being pregnant.

• 15:13Speaker 05

  78%. And if you're age 35 to 40, that percentage is 72%.

• 15:21Speaker 01

  That feels like, oh, I'll take those odds.

• 15:24Speaker 05

  Yeah.

• 15:25Speaker 01

  So if you're in the 35 to 40-year-old age group here, as I am, you, that means you have a three out of four chance of getting pregnant. And you have to keep in mind, these are rough estimates. So obviously, fertility is affected by age, but it's not the only thing that's affected by age. Miscarriage rates go up as you get older. Down syndrome rates also go up. So treat these like ballpark figures for now. But just in your mind, remember 72% for 35 to 40-year-olds. And so to me, this graph, it's like less cliff, more like English countryside. Like, I will go get a pint on my way to pregnancy.

• 16:07Speaker 01

  And this one actually made me want to call all those people we heard earlier on the phone and be like, "Psst, send this to your dad," right?

• 16:18Speaker 01

  But...

• 16:20Speaker 05

  Now, I should say that our latest research from the North American study shows stronger effects.

• 16:27Speaker 01

  Not so fast, Webster. Not so fast. What fertility looks like in North America? That's coming up after the break.

• 16:38Speaker 06

  This week on The New Yorker Radio Hour, will House Democrats try once again for impeachment?

• 16:42Speaker 00

  Let's not make a fetish out of impeachment. Let's not make a taboo out of impeachment. We understand it's not a panacea, but it is an essential tool in the constitutional toolbox that's always there.

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  Congressman Jamie Raskin joins us next time on The New Yorker Radio Hour from WNYC. Listen wherever you get your podcasts.

• 17:09Speaker 01

  I'm Molly Webster. This is Radiolab, and we are jumping right back in to what a fertility cliff looks like in North America. After the Denmark study, Lauren and her team were like,

• 17:19Speaker 05

  well, you know, Denmark is cool, but what about other countries?

• 17:24Speaker 01

  So they start the same study in US and Canada.

• 17:30Speaker 01

  Now, this graph, as it unfolded onstage, was a real humzinger. It started high on the left, and then it immediately begins to descend. It slopes down gently. There's a bit of a bump where it regains some height, and then it turns downward, this time just more steeply dropping to the bottom. Oh, that's a tricky one. Expected something else.

• 18:00Speaker 01

  This one, I felt sadder when I looked at it. I felt like this is more like, this is like less English countryside, more like a mountain biking championship sponsored by Red Bull, was kind of my, like, my feeling on this one.

• 18:15Speaker 01

  And this is what Lauren said.

• 18:17Speaker 05

  It is steep. It's something you wouldn't want to take your kid on for a walk. You would want to wear a helmet and some protective equipment.

• 18:27Speaker 01

  And do you think the different results is different parts of the globe? So like they're both truly representative of the area they're in? Or like that one is wrong and it's really a line and not an uphill and then a downhill?

• 18:40Speaker 05

  That is such a good question, Molly, and I don't know the answer to it.

• 18:44Speaker 01

  It could be differences in diet and the environment and smoking. It could be just all that bike riding in Denmark. We all just need to go to Denmark. Exactly. Honestly, it seems like I should have been having sex in Denmark when I was 30.

• 18:58Speaker 05

  Exactly. That is the take-home message of our study.

• 19:01Speaker 01

  Or I should not have been. And it was very good that I was in North America, depending on what you want your outcome to be.

• 19:07Speaker 05

  Exactly. So the Danish study, I think, is a happier, cheerier study.

• 19:13Speaker 01

  And it's true. If you look at the numbers for the North American study, they are lower. So if you're in the 37 to 39-year-old age range and you have sex, again, regularly for one year, you have a 67% chance at conception. Past 40, it drops to 55. So there are three things I took away from talking to Lauren. First, it's pretty obvious that there is no cliff. As another biologist I spoke with said, like, nothing in biology is a cliff, right? It's all just like a gradual change. It's like a gradual decline with age. And in a way, there's something about it being gradual. It kind of lets you choose to freak out where you want to freak out.

• 19:56Speaker 01

  The second thing I thought about with Lauren was that, you know, obviously, it's different for everybody. And these are just really big studies, and it's just averages, right? And the third thing was, like, even in the North American study, at like 40, 42, you still land at 50%. So it's not zero, which to me, I was like, hey, 50/50, that's not bad, right? But there was one part of the conversation with Lauren that made me think about 35 in kind of a different way. It started when she reminded me that there is, as much as I was happy about the 50/50, actually a biological deadline.

• 20:37Speaker 01

  What is the actual end?

• 20:40Speaker 05

  Oh, the average age of menopause is 50 in the United States.

• 20:44Speaker 01

  And so maybe the thing that's going on for a lot of people is it's not so much a cliff at 35, rather 35 is an age where sort of the end comes into focus. And as I was thinking more and more about the phone conversations I was having, I realized like, oh, this was playing out for everybody. Like, this is biology, but the people who are like wondering about their careers and their homes and their parents, like, they were all sort of having the same like moment where they're like, oh, there's something happening here where, where I feel something in front of me, like in the way I never had before.

• 21:26Speaker 01

  It's like, there's like this like little sliver of possibility before you all come back here in five years when you're 40 and we do this again.

• 21:37Speaker 01

  Thank you so much. So this event, which was called 30 something, happened live onstage in 2018. So it felt like it was time to maybe update the numbers. So I called Lauren back a few weeks ago and she said to me that based on sort of a larger data pool, now what they're seeing is just kind of minor adjustments. But if you're in the 37 to 39 year old range and you have sex regularly for one year, you have a 66% chance at conception and after 40, it drops to 51%. Now, this is unpublished data, but if you look at this mapped on a graph, it doesn't

• 22:19Speaker 01

  really change the original shape of the graph, as you heard me describe it in the episode. Also, the term geriatric pregnancy, you may now hear it as advanced maternal age. And they picked 35 as a cutoff because it was linked to an evidence of decline in fertility and also concern in increased risks for genetic abnormalities. So it doesn't all have to do with the fertility cliff, but it's often linked in conversation. The other thing was that Lauren looked into male data, so if you-

• 22:56Speaker 03

  Ooh, I would like to hear about that.

• 22:57Speaker 01

  Yeah, if you notice, like, in our episode, we didn't, we didn't dig into that.

• 23:02Speaker 03

  Right.

• 23:02Speaker 01

  But the male data, it's actually, it honestly surprised me. It also has a shift downward into, you know, less fecundability around 35. And it, so it does decline, though it does it at slightly later ages than for females.

• 23:22Speaker 03

  Yeah.

• 23:23Speaker 01

  One thing Lauren did say is that it took 12 years to get enough data to be able to say anything about older men with any precision, because there just aren't that many men in their late 40s or early 50s trying to have a baby.

• 23:38Speaker 03

  But it, but it sounds like it's, it's, so it's more like a, it's like a fertility gentle slope as opposed to a fertility cliff.

• 23:46Speaker 01

  Yeah, yeah. The decline starts happening at more advanced ages, and it's less of a steep slope.

• 23:53Speaker 03

  Hmm.

• 23:53Speaker 01

  And since we did that piece in 2018, there's all sorts of data that, you know, sperm does start to decrease in quality over time, and so you can get more genetic abnormalities, like, there's greater chances of that.

• 24:07Speaker 03

  Right. Well, you know, talking about sperm makes me think of donations.

• 24:11Speaker 01

  Oh, okay, we're going there.

• 24:12Speaker 03

  And talking about donations makes me think-

• 24:15Speaker 01

  Of our listeners?

• 24:16Speaker 03

  Of our listeners, and how grateful we are for all of them.

• 24:19Speaker 01

  We are so grateful, truly.

• 24:20Speaker 03

  And we, part of the reason we're so grateful is because we, like, we know what we're working on, and we're really excited about it, and we can't wait to get it to you.

• 24:30Speaker 01

  I feel like if, if listeners smash that donate button now, which is really just radiolab.org/donate, then it will help fund some of the stuff we have coming up in 2026, which for me-

• 24:43Speaker 03

  Yeah.

• 24:43Speaker 01

  -hoping it's about snail sex. And for you-

• 24:46Speaker 03

  Okay, for me, I'm working on brain balls.

• 24:49Speaker 01

  Brain balls.

• 24:50Speaker 03

  Yeah.

• 24:50Speaker 01

  How, how New Year's Eve appropriate.

• 24:52Speaker 03

  Yeah, yeah, just picture a strike of midnight on New Year's, and you're watching the ball drop, just imagine it's a brain ball dropping.

• 25:00Speaker 01

  All right. Well, how could you not donate to that?

• 25:05Speaker 03

  After that grotesque image.

• 25:08Speaker 01

  Thank you, Latif. Thank you, Diane Kelly, for fact checking this episode and Lauren Wise at Boston University for all the data crunching. And thank you, everyone, for listening, for being here for 2025.

• 25:25Speaker 03

  Yeah. Don't drink too much eggnog and have a great holiday season. And we can't wait to connect with you again in the new year.

• 25:34Speaker 01

  Bye.

• 25:39Speaker 07

  I'm Valerie Chin, and I'm from Brooklyn, New York. And here are the staff credits. Radiolab is hosted by Lulu Miller and Latif Nasser. Zorn Wheeler is our executive editor. Sarah Sandback is our executive director. Our managing editor is Pat Walters. Dylan Keefe is our director of sound design. Our staff includes Jeremy Blum, W. Harry Fortuna, David Gable, Maria Paz Gutierrez, Sindhu Niyanasambundam, Matt Keelty, Mona Magavkar, Annie McEwen, Alex Neeson, Sarah Carey, Anissa Vitza, Ariane Whack, Molly Webster,

• 26:21Speaker 07

  and Jessica Young, with help from Rebecca Rand. Our fact checkers are Diane Kelly, Emily Krieger, Anna Pujo-Mazini, and Natalie Middleton.

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