The Annotated Mother Goose includes this nursery rhyme:

First a daughter, then a son,

And the world is well begun.

Another version of the traditional ditty appears on the same page:

First a son, and then a daughter,

You've begun just as you oughter.

In these simple rhymes resides a cultural message about the auspicious life: Parent at least one boy and one girl, in the proper order.

My mother gave birth to three healthy daughters, followed by three healthy sons. It all happened naturally. The neighbors often told her how lucky she was to have such a large, balanced family. Giving birth to all those girls first meant plenty of free baby-sitters for all those boys.

When spawning offspring is left to chance, many families will fail to achieve the ideal balance Mother Goose commends. They will wind up with only girls or only boys. The baby in the family will be a boy instead of a girl. Unwilling to let nature have the last word any more, people are turning to medical science for help.

Yet there are...