Last week, we solicited your questions for economist Emily Oster, a Freakonomics favorite and author of the new book Expecting Better: Why the Conventional Pregnancy Wisdom Is Wrong-and What You Really Need to Know. Oster’s answers are below and address everything from how fertility declines with age to whether pregnant women can still safely indulge in caffeine, fish, and transatlantic travel. A big thanks to Emily — and to all of you for your excellent questions.
Q.What is your advice on whether it is safe for a woman in her early 30s to wait to have a child? I thought the book read as pretty sanguine about this, saying that women of any normal age have a better than 50/50 chance of having a baby in a year: “After 12 cycles, the pregnancy rate was around 75 percent for women under 30, 62 percent for women 31-35, and 54% for women over 35. ” But isn’t the opposite conclusion really warranted by that data? If a behavior doubled the risk for birth defects or miscarriages, I think the book would rightly point that out as problematic. And also what if a woman wants several children? – Andy
A.I think whether you find this encouraging depends a little on what you thought before. There is a lot of rhetoric about 35 being some kind of fertility cliff. This data suggests it is not, although of course fertility is declining over time. The other study I cite in the book, which looked at ever having a child (as opposed to having one within a year), suggested women aged 35 to 39 were about 90 percent as likely as those under 35 to have at least one child.
I do think the point about multiple kids is a good one. It is likely to be hard to fit three or four in if you start in your late 30s.
Q.I’m nine weeks pregnant with twins. I have been avoiding all sources of caffeine (coffee, tea, chocolate, etc.), but it has been very difficult because I love the taste of coffee and chocolate. Are decaf coffee (which has about 25 percent of the caffeine content of a cup of coffee) and small rations of chocolate safe to consume? -Catherine
A.You’ve gone too far! Virtually no sources – not the ACOG, not What to Expect When You’re Expecting – suggest avoiding caffeine all together. The most conservative recommendations suggest keeping it under 200 mg per day. You certainly are fine with your chocolate, which is very low in caffeine, and if you want a cup of – gasp – caffeinated coffee, that is okay, too.
Q.My biggest question is how can those of us without a PubMed subscription and years of statistical training get this data for ourselves? Your book covers a lot of questions that I have, but there’s no way it can address everything that’s going to come up over the course of nine months. I had been working under the assumption that the fact that a study was even published in a major journal meant that it was carefully vetted, so even if I couldn’t get more than the abstract (at best–and more likely only the pop-news “Breathing air is bad for the baby! More at 11!” coverage), I could trust that the conclusions were valid, but your careful analysis shows that that’s not always the case. Even if my doctor is up to date on the latest publications, it’s unlikely she’d have taken the time to analyze the methodology, or present me with statistical probabilities for various outcomes. It’s much quicker and easier for her to say “Don’t do that.” -Crunchy Frog
A.This is an important question – and, of course, goes far beyond pregnancy. Even if my book covered every question anyone had ever had about pregnancy (which it doesn’t), you still have to raise the kid after they are born. And you’re definitely right, even if something is published in a good journal, it may well have flaws.
I think one good guideline is: if the new warning is coming from just one study (today I saw something about how swimming during pregnancy gives your kid asthma), view it with the same caution researchers would. Interesting, but more needs to be done to learn if it is right. A second suggestion is that Cochrane Reviews (accessible free, you can Google) are typically very helpful if there is any randomized evidence. In the absence of randomized evidence, try to find a meta-analysis of non-randomized studies.
Finally, your doctor is a great resource. I think the big issue, as you cite, is the time. But if you can come with just a couple of very concrete questions, you may find that you can get a lot deeper into those issues.
Q.Can I travel by plane several times per month, possibly a couple of trans-Atlantic flights? I thought that air travel was only a risk for women close to delivery or having complications, but then I heard you should always have your doctor’s permission first. Is that really necessary? -Penny
A.Airlines will sometimes require a note from your doctor if you are very pregnant – this is because they’re worried you might have the baby in the air. And of course if you are having complications, your doctor will likely want you to stay close by.
But for an uncomplicated pregnancy not close to term, air travel is generally fine. The one issue people do worry about with a lot of air travel is radiation – because you’re high up, there is more radiation than on the ground. In very high doses (as in from X-rays), radiation can lead to birth defects and, possibly, childhood cancer. The recommended limit on exposure during pregnancy is 1mSv, although that probably doesn’t mean much to you. A flight from Chicago to Boston yields about 1 percent of this. A flight from NY to Tokyo, about 15 percent.
If you do a lot of flying, you could get close to this limit. It’s still much lower, of course, than the level at which there have been any demonstrated negative effects.
Q.What do you think about consuming fish? There seems to be some evidence of benefits (higher iq, prosocial behavior, add) but there is a risk of mercury poisoning. -vimspot
A.Unless you are having a lot of swordfish or shark, actual mercury poisoning is unlikely. But people do worry about the impacts of even lower levels of mercury on child IQ. And, in fact, it does seem that exposure to mercury can have a negative effect on brain development. Many women seem to take this to mean they should avoid fish.
This is not a good idea.
Fish is really good for you! Many fish are high in omega 3-s, which are good for brain development. By avoiding fish to get around mercury you may be losing out on brain points. A good guideline is to stay away from very high mercury fish – tuna, swordfish, shark – but otherwise enjoy.
Q.How effective are studies on what substances are harmful during pregnancy? It’s not like anyone can ethically split pregnant women into two groups and give one group three drinks a day. Also, it seems like a lot of neurological defects or disadvantages could be tough to assess. If scientists report that two cups of coffee a day is ok, does that just mean that a pregnant mother can drink two cups a day and be confident that it won’t affect her child’s birth weight, or have scientists found a way to look at effects on more complicated things like intelligence? -Andy
A.Data on pregnancy is limited, especially on issues like this. It’s hard to experiment on pregnant women – in the more medical stuff around birth this actually does happen, but not usually for questions like “Can I have coffee?” And this means the data are not perfect: women who have coffee are different in other ways. We’re left to try to identify the best studies and best research designs and learn from them.
You bring up a second issue, though, which is that there are many outcomes we could consider and studies have not been done on all of them. There is not really any evidence on caffeine and IQ – randomized or otherwise. Could be bad for kids’ IQ. Could also be good. There isn’t really any biological reason to think it would go either way.
We could ask this about anything. Is it okay to use dish soap during pregnancy? Is it okay to eat a lot of potatoes? What about using those whiteboard markers that smell so bad? At the end of the day, we may have to just admit we are accepting some baseline level of risk by just living, and, well, live with it.