Fertility Cliff

0:28Wait, you're listening. this year voice annie mckeown 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 you go i think it was it had to be probably lulu's profile of that quantum physicist kasam in palestine in palestine and just because you you feel it you're right there with them waiting in line for bread or whatever it is and all he's thinking about is quantum physics. 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. 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.

1:19You felt like you were there. You felt like you were right there. Yeah. And I think the thing is like, especially this year, how much all of these types of stories, the ones you've worked on, I've worked on, the ones we just highlighted. Truly, none of that would be possible without our listeners and our sustaining members. And so thank you, thank you, thank you. Thank you. Thank you. Thank you. Yeah. Giving us the year we've had. I mean, because let's have it's been a hard year. Right. Right. Because earlier this year, Congress eliminated all federal funding for public media and our home station, WNYC.

1:53we lost$3 million in regular, dependable annual funding. So it sort of goes with saying, I think we should definitely say it, that financial support from listeners is truly critical right now. And, you know, we're at the end of December, so time to support Radiolab in 2025 is running out. So this is like an ask to say, please consider making a year-end donation. Get us kickstarted for 2026. And if you do, we have some really killer new gift options. Yeah. Just think about it like you're buying yourself a holiday gift. And the thing you get out of it is that we got a new puzzle. I love the puzzle.

2:36It's made of like episode art from your episode. 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. And we've got so we've got a puzzle. We've got T-shirt. We've got a bumper sticker that you can, you know, put on water bottles or cars. Laptop sticker could be on anything. Laptops. Exactly. So if you want to provide ongoing support, you can join the lab, which comes with perks like sponsor-free listening, bonus content, and more.

3:18Or you can make a one-time year-end donation at radiolab.org slash donate. Go to radiolab.org slash donate. 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. Honestly, I think they do because we heard back from so many people about this episode that we decided, OK, we can give you more reporting on this topic.

4:06And 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. That sounds very dramatic. Yeah, it was so dramatic. It was so dramatic that I decided, OK, I'm going to 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 going to play part of that live event for you here. And then we're going to have updates at the end. Now, here we go.

4:48Hello, hello. How's everybody doing? All right. 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 applause applause applause applause applause

5:24Planet Earth might have been a bit bold, I will just say. Thank you for coming. This is amazing. Hi, everyone. Okay, 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 trying to hit different age groups. I wanted 18-year-olds. I wanted 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.

6:05Yes, I'll call you too. 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, 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 so there were a lot of very random conversations. And one of the things that came up in those conversations was a number. 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.

6:46Or women would be like, 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 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.

7:26She was in a relationship. She and her partner got along great. Her 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 with 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.

8:00She wasn't going to wait. And she told me that the doctors categorized her in a way that really surprised her. 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. 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.

8:37I 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, f*** 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. 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 going to go through a few graphs in this story.

9:20And 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. 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 on stage as an animation of it unfolded. He goes...

10:03and then there's like a fireball at the ends. 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.

10:30But there's one tiny caveat, and that is that the data behind this graph is crap. Yeah, this data is based on French peasants from the 1700s. And you may ask, why them out of everybody? And the idea 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.

11:16And then so I just say, you know what, like I reject this cliff because I'm done with it. 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. I know where the cliff came from. There was a very pivotal... Oh, yeah. Oh, my God. Tell me about the cliff. So the cliff, I'm pretty sure, came from this review paper written by Brochman. Who is this Brochman guy, and why does he get to draw a cliff on my fertility? He's a very famous reproductive endocrinologist.

11:55So 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 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. That's like a version of a cliff.

12:41And so then I thought, well, you know, maybe this graph, I'm reacting pretty emotionally to it. so I was like okay 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 fertility issues. So one could say it's a bit of a compromised data set. It's not really representative of everyone.

13:30So 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. We follow them forward in time for 12 months or until they get pregnant, whichever comes first. 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.

14:14Ooh, 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. This one, this one, your fertility goes up for a little while. Right? 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 um so i thought all right i'm reacting very emotionally tell me some numbers um 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?

15:1478%. And if you're age 35 to 40, that percentage is 72%. That feels like, oh, I'll take those odds. Yeah. So if you're in the 35 to 40 year old age group here, as I am, 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.

16:02Like I will go get a pint on my way to pregnancy.

16:08And 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? But... Now I should say that our latest research from the North American study shows stronger effects. Not so fast, Webster. Not so fast. What fertility looks like in North America? That's coming up after the break.

16:38I'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, Well, you know, Denmark is cool, but what about other countries? So they start the same study in U.S. and Canada. Now, this graph, as it unfolded on stage, 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.

17:26You expected something else. 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 feeling on this one. And this is what Lauren said. 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. 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?

18:10That is such a good question, Molly, and I don't know the answer to it. 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. Honestly, it seems like I should have been having sex in Denmark when I was 30. Exactly. That is the take-home message of our study. 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. Exactly. So the Danish study, I think, is a happier, cheerier study. And it's true. If you look at the numbers for the North American study, they are lower.

18:48So 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. The second thing I thought about with Lauren was that, you know, obviously it's different for everybody.

19:31And 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. What is the actual end? Oh, the average age of menopause is 50 in the United States. And so maybe the thing that's going on for a lot of people is it's not so much a clip at 35.

20:20Rather, 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. for. 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.

21:04And we do this again. Thank you so much. So this event, which was called 30 something happened live on stage 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 really change the original shape of the graph, as you heard me describe it in the episode.

21:55Also, 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. Ooh, I would like to hear about that. Yeah, if you notice, like in our episode, we didn't dig into that. But the male data, it's actually, it honestly surprised me. It also has a shift downward into, you know, less fecundability around 35.

22:46And so it does decline, though it does it at slightly later ages than for females. 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. But it sounds like it's more like a fertility gentle slope as opposed to a fertility cliff. Yeah, yeah. The decline starts happening at more advanced ages and it's less of a steep slope. 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.

23:32And so you can get more genetic abnormalities, like there's greater chances of that. Right. Well, you know, talking about sperm makes me think of donations. Oh, OK. We're going there. Talking about donations makes me think. of our listeners and how grateful we are for all of them. We're so grateful, truly. And part of the reason we're so grateful is because we know what we're working on and we're really excited about it and we can't wait to get it to you. I feel like if listeners smash that donate button now, which is really just radiolab.org slash donate, then it will help fund some of the stuff we have coming up in 2026, which for me, I'm hoping it's about snail sex.

24:15And for you? Okay. For me, I'm working on brain balls. Brain balls. Yeah. How New Year's Eve appropriate. Yeah, yeah. Just picture a strike of midnight on New Year's when you're watching the ball drop. Just imagine it's a brain ball dropping. All right. Well, how could you not donate to that? After that, after that grotesque image. 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. Yeah. Don't drink too much eggnog and have a great holiday season.

25:00And we can't wait to connect with you again in the new year. Bye. Bye.

25:09I'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. Soren 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 Bloom, W. Harry Fortuna, David Gable, Maria Paz Gutierrez, Sindhu Nianasambandam, Matt Keelty, Mona Magavkar, Annie McEwen, Alex Niesen, Sarah Carey, Anissa Vitsa, Arianne Wack, Molly Webster, and Jessica Young, with help from Rebecca Rand. Our fact checkers are Diane Kelly, Emily Krieger, Anna Pujol-Mazzini, and Natalie Middleton.

26:08Hi, I'm Idina. I'm calling from Greensburg. Leadership support for Radiolab 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. Mm-hmm.