The scene depicting a pregnant woman dispatching her mate for pickles and ice cream in the wee small hours is so trite as to qualify as a stereotype, but it's rooted in a familiar phenomenon. Being pregnant can cause unusual cravings, drive a desire to double down on old habits or bring on new and strong aversions. Yet researchers still don't fully understand the biological and behavioral mechanisms behind these hankerings [source: Manejwala].
A few patterns have emerged over the years. For example, an expecting mother's cravings tend to fall within culturally available fare; in Tanzania, women crave (in order) meat, mangoes, yogurt, oranges, plantains and soft drinks, whereas American women crave dairy and sweet foods. Connections have also emerged between pregnancy-linked hormone shifts and an increase in neuropeptide Y, a hypothalamus-born chemical messenger associated with appetite in general [source: Manejwala].
So what inspires specific cravings? It's possible that some yens are meant to counter the odd smells, strange tastes, phantom odors and food aversions that can crop up during pregnancy. But this is only one possibility and requires further study [source: Manejwala].