‘Cribsheet’ Explores The Science Of Parenting

33:05 minutes

two women, one east asian, one white, sitting on a bed with their year-old child. all three are looking at a tablet computer.
A couple and their child look at a tablet computer. Credit: Dragon Images, via Shutterstock.

logo that says 'best of 2019'If you’re a new parent, you’ve probably had one of those nights. You’re up at 3 a.m., baby screaming, searching the internet for an answer to a question you’ve never thought to ask before: Are pacifiers bad for your baby? What about that weird breathing? Is that normal? Or is it time to head to the emergency room?

Your search will bring you blogs, random websites, and the few news articles. But which sources can you really trust?

Emily Oster is a health economist and mother of two who had a lot of those same questions as she raised her kids. She dove into the data to find out what the science actually says about sleep training, breastfeeding, introducing solid foods, and lots more.

She wrote about the science of pregnancy in her first book Expecting Better. Her latest, on everything that comes after, is called Cribsheet: A Data-Driven Guide to Better, More Relaxed Parenting, from Birth to Preschool. In this segment, Oster answers listener questions and discusses common parenting myths.

Plus, Nikita Sood of Cohen Children’s Medical Center joins to talk about the underground market for breastmilk and why parents should be cautious. Want to know the 101 on milk sharing? Read Sood’s crash course below.

Read an excerpt of Cribsheet here.

Milk Sharing 101

A guide to human milk sharing.
By Nikita Sood

  • Human milk sharing is the practice of donating or receiving breast milk from lactating mothers for use by an infant not biologically their own. Formal milk sharing takes place through milk banks, which medically screen all donors, have strict regulations, pool and pasteurize all their milk, and mainly supply to Neonatal Intensive Care Units for use by premature infants.  Informal milk sharing, on the other hand, occurs between parents, oftentimes on milk-sharing websites or Facebook groups. Both the American Academy of Pediatrics and the Federal Drug Administration recommend against informal milk sharing because of the safety risks—the majority of donors are not screened, the majority of milk is not tested for contamination, and the milk is usually not tested for dilution with non-human milk (one study found that 10% of internet milk samples were diluted with cow’s milk).
  • Informally shared milk is at a much higher risk of contamination by bacteria, viruses, and other substances. Because of the strict procedures in place at human milk banks, studies have shown that the risk of contamination for formal milk sharing is low. The same is not true for informally shared milk over the internet—one study found that 74% of internet milk samples were colonized with Gram-negative bacteria, including Staphylococcus, and 21% of internet milk samples tested positive for cytomegalovirus DNA.
  • Milk sharing can be costly. Given that a 6-month-old child typically consumes 30 ounces of milk a day, milk sharing can add up. Milk bank donor milk can be a little expensive because of the medical tests and pasteurization procedures they use to keep their milk safe, milk bank donor breast milk costs $3-5 per ounce, or up to $150 a day (though it can sometimes be covered by insurance, including Medicaid).  On the other hand, informally shared milk can range from $1-4 per ounce depending on the associated diets and medications, which can add up to $120 a day plus shipping costs—but lacks the protections of a milk bank.
  • If considering milk sharing, please consult with a physician. Though studies have shown the benefits of breast milk, especially in reducing rates of necrotizing enterocolitis in premature infants, the risks associated with informal milk sharing are significant and is important that parents have a full understanding of the risks and benefits associated with the practice.

Further Reading

Segment Guests

Emily Oster

Emily Oster is the author of Cribsheet: A Data-Driven Guide to Better, More Relaxed Parenting, from Birth to Preschool (2019, Penguin Press) and Expecting Better (2014, Penguin Books). She’s also a professor of Economics at Brown University in Providence, Rhode Island.

Nikita Sood

Nikita Sood is a research assistant at Cohen Children’s Medical Center of Northwell Health, in New Hyde Park, New York.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. If you’re a new parent, I’m guessing you’ve had one of those nights every now and then and you’re up at 3:30 AM, the baby is screaming, as you ask the internet a question you never thought to ask before– are pacifiers bad for your baby? What about that weird breathing? Is that normal or not? Or is it time to head to the emergency room? I went to Google it. You get the blogs, the random websites, a few news articles. But whom do you trust? 

My next guest, Emily Oster, is a health economist, a mother of two, who’s had a lot of those questions and she’s raised her own two kids thinking about them. So she dove into the data. What does the science actually say about, let’s say, co-sleeping, or breastfeeding, introducing solid foods, potentially allergenic– like my throat– foods. 

She wrote about the science of pregnancy in her first book Expecting Better. And now she’s back with Cribsheet, A Data-Driven Guide to Better, More Relaxed Parenting, from Birth to Preschool. And it’s not just about the babies. It’s about you, too. What research is out there on parents as they fumble through life with a new kid with the emotional tank running dry? And what about dealing with the grandparents? 

We want your questions. Give us a call. 844-724-8255, 844-SCI-TALK. Or you can tweet us @scifri. Emily Oster, Professor of Economics at Brown, author of Cribsheet. We have an excerpt up at our website, ScienceFriday.com/cribsheet. Dr. Oster, welcome to Science Friday. 

EMILY OSTER: Thank you for having me. 

IRA FLATOW: And thank you for being here. There’s a lot of mythology about parenting out there, isn’t there? 

EMILY OSTER: There is. There seems like sometimes there’s only mythology and not facts. But there are some facts. 

IRA FLATOW: And so what headed you down this road to take this all on? 

EMILY OSTER: So I had kids was sort of the short answer to that question. And I found that I was trying to answer a lot of the questions that new parents have, or in the first book, that pregnant people had. And I didn’t find the answers out there that I wanted or I didn’t find the synthesis of the data. And so I started doing a lot of that myself– looking at all the papers, reading them, thinking about which pieces of evidence were better than others. And then, ultimately, the book is really a result of that. 

IRA FLATOW: Your writing reminds me of Michael Lewis of Moneyball, who had to go through all the mythology by looking at the data and change the old paradigm. 

EMILY OSTER: I’ll take that comparison. 


IRA FLATOW: All right, let’s dig into this. Let’s dig into some of these topics. You cite an interesting study in the book which links swaddling to more REM sleep. Tell us about that. 

EMILY OSTER: Yeah, so the swaddle stuff is super interesting. So swaddling, for people who are listening who are not parents, refers to wrapping up your baby pretty tightly in blankets. And people do that because they think it improves sleep. But I wanted to see if that’s true. This seems like something that maybe people would just say, that it would be an old wives tale. But actually, it’s not. And so the data there is very nice. 

So researchers wrapped up some babies in some swaddles and they put sensors on them and also videoed them. So a very comfortable baby, I’m sure, sleeping in the midst of video cameras covered in sensors. But they can look at the same baby when they’re swaddled and when they’re not. And what they see is that when the baby is swaddled, they have the same kind of initial arousal. 

So when babies are sleeping, at some point they’ll sigh or move a little bit. And then later they’ll startle and then later they’ll wake up. And that when they are swaddled, the little movements are less likely to turn into big movements and they’re less likely to turn into waking up. Whereas, if they’re not swaddled, that’s more likely to happen. So it seems like that’s the mechanism by which the swaddling is actually improving the length of sleep for babies, and for moms and dads– also good. 


IRA FLATOW: Also good. Let’s go to the phones, because there’s so many people. Let’s go to Ana in Madison, Wisconsin. Hi, Ana. 

ANA: Hello. 

IRA FLATOW: Hi, go ahead. 

ANA: I have a question for Dr. Oster. I have a 13-month-old who I’m still breastfeeding. And I know that in general in the US we tend to aim for that first year and so we’ve made it that far. But I know that in other countries and the World Health Organization recommends two years. So I’m confused about like is he getting a lot of additional benefit now for that next year? And what are the reasons to continue? As he seems to still enjoy it, but it’s a lot of work for mom. 

EMILY OSTER: Yeah. So breastfeeding, OK– so I talk in the book that the best evidence that we have about breastfeeding is really about breastfeeding at all versus not at all. So by going past a year, you’ve already gone really pretty far. And even when we look at the question of breastfeeding at all or not, the benefits seem to accrue mostly early on in life. So there’s less diarrhea, maybe fewer ear infections, fewer allergies for the first year. But some of the things that you’re told about the benefits of breastfeeding– like IQ, obesity, reductions– those actually don’t seem to be borne out in the best data, even if we look just at the basic question of breastfeeding and all, let alone looking at what we’d call extended breastfeeding. 

To answer the question about policy, I think there’s a reason that the WHO pushes further than the American Academy of Pediatrics, which is that in places with less clean water, in developing countries, there’s more benefits to breastfeeding because otherwise the kids will be having more unclean water. But in the US, I think, there just isn’t a lot of evidence that would suggest that continuing is going to have a lot of benefits for your baby, unless you want to do it which is great and is a good reason to continue. 

IRA FLATOW: Mm-hmm. We had a tweet from someone who wanted to know what is the best way to wean your kid off of breastfeeding? 

EMILY OSTER: Unfortunately, that is something I actually looked in the data– there was not a lot of data on that. Some kids will just decide that they want to stop. If you have an older kid, they often won’t decide they want to stop. And people have a lot of suggestions. Some of it’s just going to be about what is going to work for your kid. 

IRA FLATOW: Let me just go to a quick call from Rainbow in Berkeley, California. Hi, welcome. 

RAINBOW: Hi, this is Rainbow. I’m an MPH, Master’s in Public Health, as well as a PhD in nutrition. And I have read about some of Dr. Oster’s work, and it seems to discount a lot of the nutritional benefits, especially the high fiber content which helps promote a healthy microbiome for the new baby. And also, it just seems to discount the trouble that women go to to breastfeed and that it distorts the WHO’s standing that breast is best and that breastfeeding is important for at least the first year, but definitely longer. So that’s my comment. Thank you very much. 

EMILY OSTER: Yeah. I mean, so I will say what I try to do in the book is really cut into the data and what does the data actually say about the benefits. I think the discussion of the microbiome is super interesting, but also, we don’t know that much about that yet. And to the extent there are benefits, we would expect them to show up in outcomes. So the book is pretty focused on outcomes. 

And I will reiterate I actually think it’s really important that we provide supports for women who want to breastfeed. I think in some ways, the most frustrating part of this is that we’re telling people this is so important and then making it really difficult for them. So I actually have a whole chapter in the book about how to make breastfeeding work, if you want that to work for you. But what I think is more troubling is a lot of women end up feeling very bad if they can’t breastfeed or if it doesn’t work for them. I think that shame is not helpful early on in life– your kid’s life. 

IRA FLATOW: I was looking through your book and I tried to keep track of how many times the word breastfeeding was mentioned. I lost track after– I don’t know– 20, 35 times. People really are asking most about this. And I can see from our calls, I think we may have even one more. John, from Cincinnati, welcome to Science Friday. 

JOHN: Hi, Ira. It’s finally nice to get on the program. My first daughter– she’s three months old. She’s a little colicky and she has eczema a little bit all on her chest and neck. Could she be allergic to something that mom is eating, such as dairy or eggs? And would it be best to eliminate those foods from mom’s diet or would it be best to switch to formula? 

IRA FLATOW: Let me just say in advance that Dr. Oster is not a doctor. [LAUGHS] 

EMILY OSTER: That’s true. 

IRA FLATOW: Emily Oster is not a doctor and she can’t really make any recommendations individually. But we’ll speak in general terms, right doc– Emily? 

EMILY OSTER: Yeah, absolutely. Yeah. So what I was going to say is– I was, in fact, exactly going to say, I’m not a doctor. But when you look at the evidence on colic and what kinds of things affect colic, there is a bit of evidence that these elimination diets for moms can have some impact on colic. It’s not super compelling and the effects are not that big, but it’s not that hard to test. 

So if someone was in this situation– let me veer away from saying for you– but if someone was in this situation, sometimes what people will recommend is try dropping something for a few days and seeing if things improve. And that could work. It might not. And most babies do get over colic not that long from three months. So hopefully, that will improve on its own, even in the absence of any dietary changes. 

IRA FLATOW: Let me go to a tweet from Jessica Rodriguez– actually, she mentions on Facebook. And she says, “Safe sleep on back, nothing in crib, is so important. But it’s the opposite of how my newborn wants to sleep– snuggled in blankets with mom. How do you help newborns sleep safely, so I can get sleep, too?” 

EMILY OSTER: Yeah. This is such a hard space. Because, especially, newborns really struggle to sleep and parents struggle to sleep. And we do have these recommendations about safe sleep and they have a bunch of different pieces– the baby should be on its back alone in the crib, in the parents room– there’s a few of them. 

So I will say I think the evidence in favor of back-sleeping is very compelling. So the effects on reduction in SIDS, which come from a bunch of different kinds of sources, are really convincing. So even though it is true a lot of babies prefer to sleep on their stomach, the evidence suggests that the recommendation for back sleeping has been really important for policy. 

The question about co-sleeping, which I get a lot, this ends up being very fraught in the discussion. So you’ll see one camp telling you this is the most important thing you can do to be with your baby is to co-sleep with them. And then others will say this is extremely dangerous. And I think what the evidence shows is that there are some safer and less safe ways to do this. So if you’re going to co-sleep with your baby, it should be in a bed with no covers and no pillows. And you should not smoke or drink alcohol. 

If you do that, I think the data does suggest that there are some risks, although they are relatively small. And I think that we sometimes struggle to talk about risks like this and to think about them. But I think in some ways done as safely as possible, you might think about the risk as smaller than the risk you’re taking from putting your kid in the car. And so there’s a sense in which parents need to think that through for themselves and make the choice that’s right for them. 

IRA FLATOW: 844-724-8255 is our number. Talking with Emily Oster about Cribsheet, A Data-Driven Guide to Better, More Relaxed Parenting, from Birth to Preschool. I’m an older parent and I remember T. Berry Brazelton was my Bible when I was growing up. And I’ve seen a lot of stuff that I’ve talked to my kids or also adults about– they take it for granted that this is common knowledge when years ago people were talking about it in different ways. Do we have a– are you the new Dr. Spock or T. Berry Brazelton? 

EMILY OSTER: Not yet. I mean– 


–I’m not sure there will ever be a new Dr. Spock and I certainly don’t think it’s me. But I do think that there’s a space here in the modern era for trying to collate some of the noise of these studies that are everywhere. And as people are more interested in making evidence-based choices, helping people understand what does the evidence actually say. Not just what does one study say, but what does the whole literature say about some question. 

IRA FLATOW: Right. I’m Ira Flatow. This is Science Friday from WNYC Studios. Talking with Emily Oster about her new book Cribsheet. So many people are calling in. Camille Silberman on Twitter writes, “Is there a golden window for sleep training, like four to six months, just curious?” 

EMILY OSTER: Yeah, not in the data. So there is a point at which– when kids are very small, some people will tell you, you can sleep train a 10-week-old to go to sleep at night. But at 10-week-old typically cannot sleep all the way through the night. Most kids are not going to be able to sleep all the way through the night 12 hours until something like six or seven months. 

So depending on exactly what you’re trying to accomplish, the age is going to differ. I think many people, anecdotally, find it much harder to sleep train much older kids, because they are able to talk and negotiate. So maybe the window is before they can explain why you shouldn’t do it. 

IRA FLATOW: Let’s go to a quick question before the break. Kelly in Sacramento. Hi, Kelly. 


IRA FLATOW: Hi there, go ahead. 

KELLY: My daughter is four years old. And through the years she’ll go through periods where she cries a lot. Most of the time when I drop her off at school, she doesn’t cry. But right now she’s in a period where it seems like she’s crying about everything. And I’m having a hard time figuring out where is the line between the coddling her and me saying, you know what, like I just need to move on. Your crying is becoming an inconvenience every time I say no or every time I have to do something you don’t like. But I don’t know where that line is and how do we determine that? And are we coddling our kids too much right now? 

EMILY OSTER: Yeah. That is a really good question and I feel that I could have called in with that question. 


Because I feel like the book stops at three and actually most of it is about much smaller kids. And I feel like as kids get older, some of these questions get much more complicated and much less amenable to data. So the data is not going to tell you when is the right time to stop coddling. There’s a little bit of stuff in there around discipline. 

IRA FLATOW: What about younger– what about then younger kids? Crying is a normal thing, right? 

EMILY OSTER: Crying is a normal– crying is a normal thing. And we can think about questions about discipline, which is related to this. If you want to encourage your kid to not engage in some negative behavior, how can you do that? And I think the evidence there would suggest that the most important thing is consistency. So if you say if you do X, Y will happen, that you follow through. If you throw the cauliflower, I’m going to take away your cookie. You have to take away the cookie. 

That’s different than the question of how should you react to a kid who cries when you drop them at daycare, where I think probably the best evidence we have is just from what people have told you for 50 years, which is smile and wave goodbye and they’re going to stop crying when you leave. 

IRA FLATOW: And as your kids get older are you going to follow them and more evidence? 

EMILY OSTER: I don’t know. I feel like the data isn’t as good on older kids, and the questions are more complicated and more kid-specific. So I haven’t made any progress on how a second– how another book would look. 

IRA FLATOW: That is interesting. The data is not as good. That itself is a commentary. All right, stay with us for after the break we’re talking with Emily Oster, author of Cribsheet, A Data-Driven Guide to Better, More Relaxed Parenting, from Birth to Preschool. We could all use advice on that. And our number, 844-724-8255. You can also tweet us @scifri. We’ll be taking a break. Back with Emily after this break. Stay with us. 

This is Science Friday. I’m Ira Flatow. If you’re just joining us, we’re talking with Emily Oster, health economist at Brown University, about her new book Cribsheet, A Data-Driven Guide to Better, More Relaxed Parenting, From Birth to Preschool, which answers a lot of common parenting questions about everything from swaddling to breastfeeding, and answers it with evidence-based research. 

I’d like to bring on another guest now who recently presented her work on the underground market for breastmilk at a meeting of the Pediatric Academy Societies in Baltimore. Nikita Sood is a Research Assistant at Cohen Children’s Medical Center as part of Northwell Health in New Hyde Park, New York. She’s here in our New York studios. Welcome to Science Friday. 

NIKITA SOOD: Hi, it’s great to be here. 

IRA FLATOW: I have to admit something really awful. I never heard about an underground market for breastmilk. 

NIKITA SOOD: To be fair, I hadn’t either before I started doing this kind of research. 

IRA FLATOW: I feel a little better. 

NIKITA SOOD: So you’re OK. 

IRA FLATOW: Describe the market for me. 

NIKITA SOOD: Yeah, so I mean, I guess for listeners who are unfamiliar, a lot of– even though the science encourages breastfeeding for the first six months of life and ideally a year, not every parent is able to do that. And so there’s this thing called donor breastmilk where parents who aren’t able to personally supply enough breastmilk can get it from another source to feed their infant. And this practice is called milk-sharing. 

And so there’s two ways to do it. There’s milk banks, which if you think of them– sound similar to blood banks. It’s more regulated. Blood is– the breast milk is pooled. Donors are screened. Things like that. But there’s also the more popular version that’s really also getting even more and more popular is informal milk-sharing, which is this underground system where parents are able to connect directly with one another and exchange breastmilk. So a lot of that happens online, whether that’s through milk-sharing websites or social media sites on Facebook groups and things like that. And so it’s done a great job in connecting people to breastmilk they need. But obviously, it’s a little concerning too. 

IRA FLATOW: Well, you have to trust the person you’ve never seen or talked to. 


IRA FLATOW: You know nothing about that person to give your baby breastmilk. 

NIKITA SOOD: No. Exactly. And in an ideal world, you’d be able to trust another parent. And we like to think that, but I think experience has shown that you can’t really trust everyone that you meet on the internet, unfortunately. And there has been some research into whether or not this milk is safe. 

IRA FLATOW: What kind of stuff might be unsafe about the milk, for example? 

NIKITA SOOD: Yeah. I mean, inherent with any exchange of human fluids, there’s a risk of contamination. And that’s especially true for this informally shared milk. Donors aren’t screened. The milk isn’t tested. And so there’s a really high-risk of contamination with bacteria, with viruses, with even medication and things like that. 

And so there’s actually– there’s started to be more and more studies examining this kind of stuff. And there was, for example, a 2013 study published in Pediatrics that looked at milk that was purchased through a milk-sharing site online. And 74% had gram negative bacteria and would have failed milk bank level criteria. 

IRA FLATOW: Wow 74%. So give me an idea of the cost of buying. 

NIKITA SOOD: Yeah. So it’s really not an easy process. It can be actually quite financially burdensome. I guess for a sense of comparison, formula typically costs around $0.08 to $0.31 an ounce. And given that– I think it’s a three-month-old baby will consume 30 ounces a day. That amounts to maybe as much as $10 a day to feed that child. Informally shared milk can be free on certain sites where you just pay for shipping. Although, it’s not screened, it’s not medically safe. But you can also have to pay as much as $4 for some of that milk, which adds up to about $120 a day. 



IRA FLATOW: 844-724-8255. I want you to stay with us for the rest of the hour. Is that OK? 

NIKITA SOOD: Yeah, thank you. 

IRA FLATOW: Because we have lots of questions here. Emily, what do you think about this breastmilk market? 

EMILY OSTER: So this is a super interesting market. Economists like markets. I think there’s a sense in which we have generated an attitude that breastmilk is so sacred and so important that you would be better off giving your kid breastmilk that has bacteria in it than you would giving them formula. And I think that that’s probably in many cases not true. 

And I think it is part of this cult around breastfeeding. And I do think that it is maybe a byproduct of some of the claims that are made that are not all as well-supported in the evidence. I would rather have us spend more time helping women try to breastfeed and then not shaming them if they can’t. 

IRA FLATOW: Here’s a tweet from Cara. It says, “Has Dr. Oster looked at any research about cannabis use and breastfeeding as marijuana restrictions loosen?” 

EMILY OSTER: No. It’s– go ahead. 

IRA FLATOW: No. Well, Nikita, have you come across this in talking with moms looking for breastmilk, that this is a concern of theirs? 

NIKITA SOOD: Yeah. I mean, this is definitely not the first time I’ve heard this type of question. What we tend to do is actually for this study, we were looking a lot on parenting blogs which influence a lot of the parenting advice like you’re saying Dr. Oster. And so we found a lot of questions about cannabis use and breastmilk and whether or not that’s an issue. Unfortunately, I haven’t personally done any research into it and I think more research needs to be done. But I would– 

IRA FLATOW: Yeah. You would think, Emily, that this sure is going to come up with the loosening of cannabis restriction. 

EMILY OSTER: Yeah, it is. But I think until we see more time with these loosened restrictions, it’s a very hard thing to study. Because now most of the studies would be based on a time when the cannabis use was illegal and so people don’t want to tell you. Or the kinds of women who are using cannabis are more different. And so I think we will see more of this over time, but I don’t think the evidence is there yet to say either way. 

IRA FLATOW: Mm-hmm. 

NIKITA SOOD: I agree, too. I think even beyond just with seeing cannabis in breastmilk, I think in general what I’ve is that there’s not actually that many studies that have been done looking at informally shared milk and donor breastmilk, in general, even though this has been around for, I think, longer than cannabis has started to become legal. And so I definitely think there needs to be a lot more research done in these areas, so that we can give definitive recommendations and say what the science says about the risks. 

IRA FLATOW: Before I go to the phones, let me ask you, Emily, as a possibly soon to be grandparent myself, how do– what’s the best way to treat your mother, your father with the kid, with the newborn? 

EMILY OSTER: You mean like how should they treat the grandparents? 

IRA FLATOW: Yeah, how should they treat the grandparents? How should the grandparents treat the kids or their kids or the grandchildren? 

EMILY OSTER: So it’s interesting. I don’t think there’s a huge amount of data on this. I think being supportive is probably the most important thing. But I think part of what’s hard about the interactions between grandparents and grandkids is that there are changes and recommendations over time and it can be hard to not share the experiences that you had, because, of course, they are in many ways very valuable, but also in some ways outdated. 

So people bring this up to me all the time around the issue of back-sleeping, that when we were kids you put your baby to sleep on their stomach. Now the recommendation is to go to sleep on the back. And I think that a lot of people are getting tension with their parents about that change in recommendation. It worked for me, you should do this too. 

IRA FLATOW: You said in the book that you should have a frank exchange of views with your kids– let me put it that way– and have that discussion about how to treat each other. 

EMILY OSTER: Yeah, absolutely. I think that talking things through. 

IRA FLATOW: Yeah. Just let me go to the phones– speaking of talking it through. Let’s go to Christina in Noonan, Georgia. Hi, Christina. 

CHRISTINA: Hi there. How are you doing? 

IRA FLATOW: Hi there. Go ahead. 

CHRISTINA: Yes. My question would be basically about letting your child cry to go to sleep. What would be the recommendation about that? And if there is any data that supports crying for so many minutes versus holding the baby, soothing it to sleep, and at what age would you recommend allowing them to cry it out? 

IRA FLATOW: Mm-hmm. 

EMILY OSTER: There’s a lot of evidence on this. And I think that people worry about two things. One is, does it work? And the other is, is it going to damage my kid? And this is a place where unlike in some aspects, we actually have very good data, I think, because we have randomized trials, some of which follow kids until they’re five or six– so not just two days after this happens. 

And I think broadly the evidence is very reassuring. Sleep training, letting your kid cry it out, does improve kids sleep. It also improves parents sleep and actually has pretty big effects on depression, on reducing maternal depression, improving marital satisfaction. So I think there are some reasons to do it. 

In terms of long-term impacts, there’s no evidence of negative long-term impacts or any long-term impacts in any direction. So I think that for parents who want to do that, that is really reassuring. Doesn’t mean everybody’s going to want to sleep train their kids. That is a pretty personal choice. And it is very hard to listen to your kid cry. But it does have some of these good effects down the road in terms of improving sleep. 

There actually isn’t too much guidance about which of the many different technologies– should you go in every three minutes? Should you go in every 10 minutes? Should you not go in at all? All of these things seem to work fine. You pick a lane and stick with it. And that’s kind of what the guidance is. 

IRA FLATOW: Nikita, you also looked at the history of wet-nursing. Tell us about that. Isn’t milk-sharing just like a modern version of wet-nursing? 

NIKITA SOOD: Mm-hmm. That’s probably one of the most common themes we saw in our study when we were getting a lot of information from mothers who had participated in milk-sharing. And so we wanted to look into that so we could say definitively whether or not it is comparable. And I mean, wet-nursing has been around for so long, I mean, centuries upon centuries, thousands of years. It’s mentioned in the Bible and a lot of religious texts. 

And the fact of the matter is is that in those ages, wet-nursing was really the only way of feeding a child if the mom couldn’t breastfeed personally, because there was no formula. There were no safe bottles. There was no pumping for later use or storing breastmilk. And so it was out of a necessity. And because of that, it was very, very well-known. It was very common. And therefore, it was very well-regulated. 

And so there were contracts that existed between wet-nurses and the families that employed them. There were medical tests that were required. And so it lends itself to being more similar, actually, to the milk bank process, which is where there’s medical screening, there’s strict regulations– things like that– than this underground milk-sharing market that’s taking place online. 

IRA FLATOW: We’ve had some tweets from a couple of people who’ve said the same thing about– Amanda says, “Proud milk-sharer. I donated to over five families. I never asked anyone for a dime. It’s an act of love from one mom to another.” And we’ve had a few similar tweets. I guess that is opposed to what you would say get– the prices you were mentioning at the milk banks, right? 

NIKITA SOOD: Yes. No. Definitely. So I mean, even milk bank, because of the processes of medical testing and things like that, it is quite expensive. It can be as much as $3 to $5 an ounce. And we have– I mean, we’ve encountered thousands of women in our research who have participated in milk-sharing who have donated so many ounces and done a lot of good work. And I think it’s great, but I think that there needs to be also regulations in place that we know that the risks that are being undertaken and we can make sure that this milk that’s able to be donated can be done in a safe way, ideally through a milk bank. 

IRA FLATOW: I’m Ira Flatow. This is Science Friday from WNYC Studios. Talking with Emily Oster and Nikita Sood. Emily, we basically talked, I’d say, 90% about the mothers here. Any advice, any of the research talk about fathering? 

EMILY OSTER: Yeah. So there’s– so I think one thing that I spent some time on in the book about fathers is when we think about postpartum experiences, there’s a lot of emphasis on maternal depression and making sure that women are not depressed. To be clear, there’s not enough emphasis on that. But there is more than on dads. But one of the things that I think people are increasingly recognizing is that postpartum mental health issues can affect all of the people in the family. 

And I think that’s a place where we could be a little more cognizant of the fact that when people are tired, that affects their mental health. In general, this is a stressful experience and we want to be careful to be paying attention to the mental health of all the parents, not just the birth mom. 

IRA FLATOW: Any research on how much more stressful single-parenting is? 

EMILY OSTER: There’s not that much. I mean, I think the circumstances that lead to single-parenting are pretty varied. And so the answer to that is likely to vary depending on whether you’re a single parent by choice or not by choice, and how involved the other parent is. And so that makes it hard to draw broad conclusions. 

IRA FLATOW: Ed tweets, “Baby-led weaning for solids seems to be on a trend. My wife and I freak out after seeing our seven-month-old gag and trying solid foods.” Thoughts? 

EMILY OSTER: So there are a lot of different good ways to introduce food to your kids. And so one of the things I think was actually surprising to me is I was given when my daughter was born– or daughter was old enough for this– I was given this strict instructions about rice cereal, and oatmeal, and then these vegetables, and all in this particular order. And I think it turns out that there’s no particular reason to introduce things in that way. There’s also nothing wrong with doing it in that way. 

But people have increasingly been interested in this idea of baby-led weaning. It has some value because it’s in some ways easier to not deal with baby food. But people do worry that their kids gag. I think the evidence suggests that it isn’t dangerous. Although, it also doesn’t have some of these benefits like lower obesity that people have touted. So if you want to go for that, that’s great. If it makes you nervous, do something else. 

IRA FLATOW: And one thing you might do is read the new book by Emily Oster. Her new book is Cribsheet. We have so many people– so much more time that we don’t have. We have an excerpt of the book up at ScienceFriday.com/cribsheet. You’ll also find Nikita Sood’s list of advice up there if you’re a pregnant parent considering buying breastmilk. And that’s at ScienceFriday.com/cribsheet. 

Thank you both. Nikki Sood is Research Assistant at Cohen’s Children’s Medical Center, part of the Northwell Health in New Hyde Park, New York. Emily Oster, health economist at Brown University, author of Cribsheet. Thank you both– 

NIKITA SOOD: Thank you for having me. 

IRA FLATOW: –for taking time to be with us today. 

EMILY OSTER: Thank you so much. 

IRA FLATOW: You’re welcome.

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