Finally, there's the question of how Mom's distress during pregnancy affects kids' actual development. Here, too, the data are mixed. The strongest studies try to separate the influence of maternal stress during pregnancy from the stress or adversity, after birth, in children's home environments. (Often there is a correlation between the two.) This research also tries to assess children directly, rather than relying on parents' reports about their behavior. The most persuasive of these papers suggest that mild to moderate stress during pregnancy doesn't hamper babies' maturation — if anything, it may slightly hasten it. In one study, fetuses whose mothers reported higher levels of distress tended to be more active in utero, a positive developmental sign. In another study, newborns of more distressed women conveyed electrical signals more rapidly along the nerve from the ear to the brain, also a marker of neural development. And in a study of toddlers, the results were more striking still: Two-year-olds who were exposed in utero to more maternal distress, including depression or anxiety, scored higher on a standard measure of child development. "It just looks like they mature a little faster," said Janet DiPietro of Johns Hopkins, who conducted these studies. In other words, there is little evidence that maternal stress during pregnancy is bad for babies.
DiPietro, who is one of the foremost experts in the world on fetal outcomes, says she finds the continued intensity of work on these questions puzzling, given the findings so far. "I'm trying to get out of the stress stuff!" she told me. So should the rest of us. It's time to stop worrying that our worrying will prevent us from reproducing successfully. Survival of the species, it turns out, just isn't that fragile.