There's more than one right way to have a baby. What Maggie Koerth-Baker learned about evidence-based pregnancy, risk, and the choices we make about healthcare.

Can you have a beer while you're pregnant?

Is it safe to give birth at home, instead of in a hospital or birth center?

Other than the fact that they both concern pregnant women, these two questions don't seem to have a lot in common. Truth is, though, they're closely intertwined. Both are implicitly expect a solid "yes" or "no" response. And, in both cases, solid "yes" or "no" answers are sorely lacking. Instead, what you get, when you look at the evidence, is a collection of data that tells you something about risk … but not really enough to tell you exactly what decision you ought to make about that risk.

These two questions are representative of many preggo-centric healthcare decisions. They also serve as brilliant examples of why "evidence-based medicine" might not mean what you think it means.

Several months ago, I set out to read a bunch of pregnancy books and report back to you on some of my favorites. I wanted to put together a list that would appeal to pregnant science dorks — those of us who enter the world of reproduction thinking about it less as a sacred, spiritual journey and more as a chance to participate in a really awesome DIY experiment. (I am my own 3D printer! Jealous, gentlemen?)
I found eight books that filled different niches in my library. All of them put a heavy emphasis on scientific research and on not just telling me what we know, but explaining why we think we know it. All of them taught me stuff that was cool and useful and helped me think about my own pregnancy and upcoming parenthood in a different way.

But I noticed there was something else they all had in common, as well. None of them were big on flat-out telling pregnant women what was right and what was wrong. If you set out to read these books hoping for a set of tidy rules that would make you the best pregnant lady ever, you were going to be disappointed. Ditto if you were looking for a guide to the ideal birth experience. Mega ditto if you were hoping for tricks that would ensure your baby turns out to be smarter, less weepy, and a better eater and sleeper than all the other babies in your neighborhood.

And that seems surprising. After all, the whole reason we look to evidence is because it's supposed to produce better outcomes than relying on anecdotes, tradition, trendiness, and/or Dr. Oz. Evidence is supposed to be the cooly rational thing that separates us from the unwashed, emotional masses. Shouldn't the evidence-based books be more confident in telling you exactly what to do to produce the best possible outcome, rather than less?

"People have misunderstood evidence-based medicine as cookbook medicine," Jeremy Howick told me. He's a research fellow at Oxford University's Centre for Evidence-Based Medicine. "But David Hume says you can't derive an 'ought' from an 'is'."

What he means by that is that simply having evidence is not the same thing as knowing the "right" way to do something. At least, not most of the time. Not when it comes to healthcare. And those two key questions about pregnancy — Can pregnant women drink? Is homebirth safe? — are brilliant examples of why this is true.

There have been studies done looking at the outcomes of both questions. But, in both cases, none of those studies are ideal. In fact, ideal studies probably aren't possible here, because they would require you to randomly assign pregnant women to make decisions they don't necessarily want to make. (I'm sorry ma'am, but we're going to have to ask you to take this tequila shot every Thursday for the next 9 months.) Instead, you're left with a lot of observational data — some stronger, some weaker. None of it telling you exactly what you want to know.

In the case of drinking during pregnancy, the data gets messy because a lot of it is based on women remembering their own habits (sometimes years later). Other studies lump women who have one alcoholic drink a week in with women who have as many as eight — and those studies may or may not separate the women who had one single drink, every night of the week, from the women who have five drinks one night and three the next. (Differences that seem to matter a lot when it comes to how the alcohol affects a fetus.)

For home births, a lot of the problems stem from record-keeping — if someone starts out giving birth at home and then gets rushed to the hospital with complications, some places will count that as safety demerit for home birth, other places for hospitals. There are also some big issues with the fact that the women who choose home birth are generally in demographic groups that are less likely to have pregnancy complications, to begin with.

With both questions, the evidence gives you an opportunity to make a decision. From reading the books I read, I learned that home birth is probably safe, provided you don't have any complications and you're able to get to quickly get to a hospital should any arise. That's a choice, not a prescription. Two women can look at that sentence and come to very different, evidence-based conclusions about what's right for them.

Same thing for drinking during pregnancy. It's a fact that binge drinking and/or excessive drinking will cause problems for your child later in life. Sometimes, those problems are severe. Nobody knows exactly what "excessive" means, though, and there's good reason to think that a drink a month or a drink a week aren't going to hurt anything. Again, you're left with a choice.

What amount of risk are you comfortable with?

And that's not a question the evidence can answer for you.

"Everybody is different. Every situation is different," says Kay Dickersin, who directs the center for clinical trials at the Johns Hopkins School of Public Health. She gave me an example from a different side of women's health — the options available to women who are older, done having children, and tired of suffering from abnormally long, painful, bloody periods that they can't seem to get under control. For them, there's two choices: A fully hysterectomy or an endometrial ablation (essentially, doctors destroy your uterine lining, but leave the uterus, itself, in place). The hysterectomy comes with a hospital stay, a higher risk of infection, and at least six weeks of post-surgical recovery time. But you know for certain you won't be bleeding again. The ablation, on the other hand, trades a risk of not totally fixing the problem for the convenience of a faster recovery and less risk of infection.

Which you choose isn't really about the medical evidence — they're both safe, they have roughly equal levels of patient satisfaction, they're both effective. Instead, it's about your life, your work schedule, your values and your personal preferences. What risks are you comfortable with?

The truth about evidence-based medicine is that it actually means you have more decisions to make, not fewer. The hard facts only take you so far. To know what to do, you have to layer them up with the soft, squishy bits that make up your life — and that includes emotions, personal beliefs, and even what choices your mother and best friend made. Doing that isn't ignoring evidence and snubbing science, Dickersin and Howlick say. It's using the science in the way it's supposed to be used … the only way we can use it.

So, here's what I learned reading evidence-based pregnancy books. I learned that I'm most comfortable having my baby in a hospital, under the care of a doctor I trust. I learned that, while I'm not willing to take the risk of home birth, I am willing to take the risk of having a beer a couple times a month in the third trimester. And I learned that, even though somebody else might make exactly the opposite decisions, we're both still making evidence-based decisions. The best pregnancy books are the ones that acknowledge that reality and don't try to convince you that the decisions of the author are the only right answer.

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