Pregnancy: the hard facts

Everyone needs a friend like Emily Oster. She is brilliant at making decisions and can cut through hefty data like a cerebral samurai sword. An economics professor at the University of Chicago, Oster teaches MBA students how to make good business choices and employs economic principles to challenge the established line on anything from health policy to the division of household chores.

So naturally, when Oster decided to have a baby, she set out to arm herself with all the numbers to do with pregnancy and childbirth. This turned out to be much harder than she had expected. In fact, she quickly became exasperated by the scarcity of hard facts and consistent advice that was available from doctors. Instead she was presented with a long list of rules, and found prenatal medical care infantalising.

The good news is that the knowledge Oster eventually amassed is no longer only available to her eager pregnant chums, because she has collated her findings into a book. Expecting Better: Why the Conventional Pregnancy Wisdom Is Wrong – and What You Really Need to Know, is the anti-What to Expect When You're Expecting. Where that bestselling pregnancy manual was adapted into a slushy romcom, Expecting Better would have to be more of an Erin Brockovich-style quest movie. There's nothing girly about this book.

There are many reasons, says Oster, why pregnancy guidance is so poor. There's the short and hurried nature of medical appointments, and the way that information gets squished into one-size-fits-all pamphlets. "I also think medical training doesn't focus that much on the [patient] decision-making aspects," she adds, sat poised in her small campus office. And on top of these factors, the rules are sometimes based on out-of-date figures.

Take amniocentesis, an optional procedure where a sample of amniotic fluid is taken to test for chromosomal abnormalities, and which is said to carry an increased risk of miscarriage. In the US, only women over 35 are recommended to undergo it because this is the point at which the chance of having a miscarriage is supposed to be outweighed by the chance of having a child with a chromosomal disorder. Deciding whether to take the test can itself be extremely stressful. And when Oster discovered that the miscarriage risk she was quoted, of one in 200, was the same figure her mother had been given in 1985, alarm bells rang. Surely technological advances would have made it safer over time? The book details the many relevant studies Oster looked at and concludes that the risk is actually more like one in 800. The NHS website, meanwhile, offers an even more archaic figure of 1 in 100.

There are other factors, too, that make it illogical to have a blanket cut-off age after which amniocentesis is deemed appropriate, including individual medical history, but not least the assumption that everyone believes it would be worse to have a child with Down's syndrome than a miscarriage. "In fact," says Oster, "if you read official recommendations from the guys who make the obstetrician rules, they also don't think this is a good rule, they also think it should be more nuanced and that people should be involved in this conversation more." Trouble is, updates such as this are slow to filter down into general practice.

Oster puts all aspects of conception, pregnancy and birth advice under similar scrutiny, ending each chapter with lists of the salient facts under the heading "Bottom line" – from fertility (it doesn't decline as fast as you might expect and it is not necessarily curtains once you pass 35) to epidurals (effective pain killer but increases the chance of some complications for mum) via getting your roots done (no problem).

Food and drink restrictions are given reassuringly short shrift. For example, what's the deal during that agonising two-week wait between possible conception and confirmation of pregnancy? Should women behave as though they are pregnant, just in case, or carry on as per usual? Before she researched this topic, Oster gritted her teeth through a hen weekend in Las Vegas, consuming "two measly glasses of wine", only to discover that drinking more in moderation wouldn't have hurt the baby anyway. "I can't believe I didn't figure this out before Vegas," she writes.

Some areas were easier to research than others. The issue of pregnancy weight gain, for example, was the toughest to uncover hard facts about. "There's a lot of discussion in the US because of the obesity problem," says Oster, "that too much weight gain in pregnancy is going to make your kid really fat later and that's terrible and so on." However, she spent a lot of time on the academic literature and found nothing that indicated that excessive weight gain would affect the child, "in a way that was at all compelling." When she was writing this chapter, Jessica Simpson was the pregnant celebrity du jour and had piled on the pounds. "People were on TV saying 'this is so terrible' – you have no idea that it's so terrible," says Oster.

When it comes to pregnancy, it is raining misinformation, and to counter this, Oster has distilled all the stuff you would learn, she says, "if you spent your entire pregnancy on the internet reading medical literature". Reassuringly, however, she did make one slight error – a common oversight for first-time parents, for whom the reality of ending up with an actual baby is hard to imagine: focusing entirely on pregnancy and birth and not on what happens next. This is when, she realises while holding her new daughter, the real decision making begins.