The What to Expect book on Pregnancy has been panned all over the Internet; just do a search for "Pregnancy book I found most rubbish" or along those lines.
The advice about limiting heartrate during exercise is obsolete & really annoys me. The idea is to prevent aerobic exercise -- basically, anything that gets you feeling like you're working hard. The ideas behind preggos not doing aerobic exercise, I'm pretty sure, are based on 1930s-1950s studies of what happens to physiology during aerobic exercise. It was observed that during aerobic exercise blood gets diverted from internal organs to muscles. Therefore must be bad for pregnant women, right??
EXCEPT, the studies were done on college-age young men. And laboratory animals. Neither of which describes pregnant women. The actual epidemiological studies show positive outcomes for all women who continue with aerobic exercise during pregnancy, with one exception. The babies of exercisers tend to be smaller, by about 1/2 lb on average. And higher birthweights, while tending to mean more complicated births, also seem to lead to more clever, more sexually successful, more emotionally happy adults (if you believe clinical studies relating birth weight to these things). However, one study suggested that the birthweight difference has to do with body fat, rather than height. And that these children may have a life-long, inbuilt programming to tend to carry less body fat than is average in the population. Sounds like a good thing with obesity almost epidemic...
OBVIOUSLY, a PG woman should only exercise within comfortable zones and go for a cautious idea of what feels ok rather than pushing her limits. But if you know you can trust yourself to stop when you feel too tired, then ignore the heartrate stuff.
Quick REFs, not all of equal quality:
Positive body image .
General info .
More detailed Info .
Benefits, but also when Exercise may be contra-indicated for PG women .