Emily Oster really hopes you don’t need to buy her new book. The 44-year-old tenured Brown University economics professor and firebrand has published a handful of bestselling titles, all focused on childbearing and child-rearing. “I always say I’m not going to write another book after I write a book because it feels like so much work,” she said. “The first three books really track my own journey, from pregnancy to raising little kids to having older kids.”

But the fourth installment in her “ParentData” – also the name of her blog, podcast and newsletter – quartet, The Unexpected, swerves into thornier territory than its predecessors: pregnancies with complications, and the risks inherent in any subsequent pregnancies. For the first time, she is not writing about her own experiences. “I was inspired by the questions that I got from other people rather than the questions that I had myself,” she said.

Pregnancy complications are not a niche topic. About 50% of pregnancies involve one of the complications Oster outlines in her new book. Working with her frequent collaborator, the New York-based maternal fetal medicine specialist Nathan Fox MD, Oster sifts through reams of data on a range of conditions and outcomes relevant to pregnancy, including pre-eclampsia, miscarriages, C-sections and gestational diabetes. In her straightforward delivery, she explains the known causes of various unhappy scenarios as well as the likelihood of their recurrence in subsequent pregnancies.

Oster – a mother of two who has 374,000 Instagram followers and fans in Mandy Moore and Amy Schumer – has made a name for herself with her no-nonsense breakdowns of conflicting data sets that concern maternal health and best practices. “I’m trying to create value,” she said. “I’m trying to create meaning for people or help people to the extent that a book can provide help.” She has also made waves for her controversial takes, such as making the case for schools returning to in-person learning during Covid, or for pregnant women in their second or third trimester enjoying a glass of wine if it so appeals.

Oster spoke with the Guardian about what to expect when you’re anxious about expecting.

One of the most striking things that comes through in your new book is how little time doctors tend to spend with their patients, whether they’re pregnant or not.

I’m helping women figure out how to use that time as productively as possible, because we aren’t going to get two hours. It’s more like you’re getting 15 minutes, and you have to use that time productively. And that’s very difficult to do if you haven’t come in with a sense of where you want to get to at the end of the conversation.

One of the points you drive home is that you don’t have to be the passive one at a medical appointment. You offer scripts for your readers – you also inspired me to take a more active role with my doctors.

Those tools [in my book] are potentially quite useful. For almost any interaction with a medical provider, whether it’s in pregnancy or [if you’re meeting] with a pediatrician or an endocrinologist, you have to have an actual sense of what you’re trying to accomplish with this visit. You’re going to get there much faster.

You are known for coming to eyebrow-raising conclusions. Is there anything in this book that you expect will be controversial?

I guess we’ll see. I’m always surprised. But I do think in this case there isn’t as much that I would put in that category.

How does the US supreme court Dobbs decision, which led to more than a dozen states banning most abortions, relate to the issue of prenatal care?

There are definitely [cases with] pregnancy complications where a limit on choice has impacted people’s ability to make decisions in their pregnancy that would serve their own health.

The most extreme parts of this come up when we’re talking about the late first or early second trimester pregnancy losses. The procedure that would be done to make it safe for someone to miscarry is basically the same procedure that you would do in a second trimester abortion. [In some states] those abortions are restricted, so people are not able to get the pregnancy care that they need.

And when we have a draconian abortion law, doctors simply don’t know how to do that because they have no experience doing the procedure. So a lot of women will have to travel out of state.

Much of the information out there regarding pregnancy and childbirth is incredibly difficult to compute. Do you feel like there is an element of sexism at play in terms of how abstruse the studies are?

There are a lot of questions that we don’t have answers to. Whether that is because of sexism, or whether that is because it’s difficult to monetize the answers to some of those questions … I think both of those are going on.

Your previous books had an autobiographical bent. But you didn’t have terribly difficult pregnancies. How did you end up writing about pregnancy complications?

A lot of people read [Oster’s 2013 book about pregnancy] Expecting Better. And many of those people would then reach out if something happened, saying: is this gonna happen again? I had prolapse, and how do I fix that? I had gestational diabetes, am I going to have it again? And then there were the people who reached out in really, really tragic situations. I wanted there to be something I could point them to.

Is there a particular pregnancy complication you’d like to highlight?

When we think about complications like pre-eclampsia, which can be life-threatening for mom and for baby, could there be more research? Sure. Do I wish we understood the drugs [used to treat such conditions] better? Absolutely. But there’s so much incentive on the medical side to learn about these because it really is sometimes a matter of life and death for mom versus baby.

When we talk about something like vaginal tearing or prolapse or postpartum depression, we don’t research those enough. Maybe because they’re not treated in the hospital. They’re not medicalized enough. Or maybe it’s because they’re embarrassing, and people don’t want to say, we need more research so we can understand: why has my uterus fallen into my vagina, and how can we fix that?

Because the experience of walking around with your organs coming out of your vagina is uncomfortable and embarrassing for some people and gets in the way of other things people want to want to do, right? But we don’t talk about that, even though it’s pretty common.

I had fairly easy pregnancies and childbirths, but vaginal tearing and postpartum anxiety were two things that I didn’t learn about until after the fact. I wasn’t prepared for them because they’re not part of the conversation.

I think some of the conversation is about when something becomes a problem and when you should be talking to your doctor about it. Of course, the answer is almost always when you are uncomfortable or if you’re worried, but there are questions people have about, like, nausea and vomiting – like, how much is too much? How would I know if this was really something I should actually be pursuing [medical treatment for]?

What did you learn while working on this book that was most surprising?

I suspect the thing most people will find most surprising was the frequency of stillbirths. I say that not to freak people out and to scare people, but stillbirth [happens in] one in 160 births – that’s a lot more common than some things, like chromosomal abnormalities; the risk of Down’s syndrome for an average person is about one in 700. It’s not that I think you should be walking around thinking about this. But the experience when it happens is often so deeply isolating.

What is next in the Emily Oster oeuvre?

My academic research is about health economics and statistical methods. People ask questions about why people don’t make the health decisions that we think that they should, and how we can learn from observational data, and what are some of the problems of learning from that kind of data when it’s correlation, and not causality. I haven’t settled on anything yet, but people say to me: are you going to write about raising teens, or helping ageing parents?

You’re known online as the woman who says that pregnant women should not feel afraid to drink a glass of wine in their second and third trimester. What kind of wine do you like to drink?

Hmm … a nice Australian or New Zealand sauvignon blanc.

That’s funny! I thought you were going to say something fancy, like a 1972 Barolo.

No, now that I’m old, I don’t drink red wine anymore. Red wine is not my friend.

The Unexpected: Navigating Pregnancy During and After Complications by Emily Oster and Nathan Fox is out via Penguin Press on April 30.