Katie Couric recently had the honor of addressing this year’s graduating class at her alma mater, the University of Virginia. While researching material for her speech, she came across Dr. Meg Jay’s book "The Defining Decade: Why Your Twenties Matter - And How to Make the Most of Them Now." According to Dr. Jay, 80% of our defining decisions—such as getting married and having children--are made before we are 35, and 70% of lifetime wage growth happens in the first 10 years of our careers. These are sobering statistics given that many of the twentysomethings Dr. Jay sees in her practice are slowly wasting this precious decade of their lives. They are still waiting for Mr. or Ms. Perfect to arrive, so they put off marrying. Or they are still waiting to “find themselves” before they commit to a . Children are a distant possibility, perhaps when they close in on age 40.

While there is much to be said for Dr. Jay’s analysis and her exhortation to get out there and live, there lies a deeper dilemma in the statistics she cites, a dilemma she discusses only briefly towards the end of her book, a dilemma that is hiding in the statistics cited above: Your prime reproductive years overlap exactly with your prime career-building years. Many twentysomethings who seem to be dragging their feet when it comes to embracing full adulthood are in fact impaled on the horns of that dilemma.

It is impossible to evaluate the rationality of a decision without asking the question: compared to what? A rational choice is the one that is most likely to bring you what you most want. Given that both childrearing and career-building make enormous demands on one’s time and energy, the choices on the table are to (a) put off having children until your career is settled, (b) put off building your career until your family is settled, or (c) try to do both.

Let’s look at option (a). While the Zeitgeist suggests this is the preferred option (after all, celebrities are having babies at age 40, aren’t they), the plain fact is that putting off childbearing until your late 30’s is like playing Russian roulette. Fertility takes a nosedive after age 35, and that is true for both men and women alike. Couples who wait until their late 30’s to start their families will likely require medical assistance to conceive and/or to maintain a . The incidence of several types of birth defects and syndromes (such as ) also rise with maternal and paternal age.

The consequences of options (b) and (c) overlap so greatly that I will consider them together. The best way to communicate what happens to those who strive for work-family balance is to cite some rather disturbing statistics from the Harvard and Beyond Project, in which economists Claudia Goldin, Lawrence Katz, Naomi Hausman, and Bryce Ward tracked three cohorts of female Harvard graduates (1970, 1980 and 1990) fifteen years after they received their degrees. The results showed the striking impact of children on women’s careers.

Among those who had no children and a law degree (J.D.), 83% were employed full time.

For those who had one child, only 64% were employed full time, and for those who had two or more, fewer than half (49%) were employed full time, and the values were pretty much the same for MBAs, PhD., physicians, dentists, and veterinarians.

MBA’s who took time off from full time work had incomes that were 53 percent lower than those who didn’t. The losses for both PhD’s and JD’s were 34 percent. The loss for physicians’ dentists, and veterinarians was 16 percent.

So why don’t these women simply take advantage of all the “quality” daycare that is available? Well, here's that problem in a nutshell: Many have been persuaded that too much daycare too early in childhood is detrimental to . Here is just some of the evidence:

According to a report by the U.S. Department of Human Health & Human Services, among infants whose mothers return to work full time before their infants reach six months of age, only half are securely attached to their mothers.

The Quebec Daycare Study followed children in government subsidized daycare facilities beginning in 1997. The report concluded “For almost every measure, we find an increased use of child care was associated with a decrease in their well-being relative to other children.”

A recent study conducted by the U.S. National Institute of Child Heath and Human Development (NICHD) concluded that "The more time children spend in childcare from birth to age four-and-a-half, the more adults tended to rate them as less likely to get along with others, as more , as disobedient, and as aggressive.” It also found that “group care is more punitive than other forms of childcare.”

Rest assured: this is not a call for mothers to leave the workplace and return to the kitchen. But it is a call to wonder about the real meaning of Katie Couric’s statement that “70% of lifetime wage growth happens in the first 10 years of our careers.” From the vantage point I have just outlined, this does not seem like something to be proud of. It seems instead like a call to re-think our ideas of what constitutes a successful career and a successful life.

What if, like Alicia Florrick of the TV show The Good Wife, young professionals are allowed to step out of the fast lane while their children are young, and return without penalty when they are older? Given that the average worker spends approximately 45 years in the workplace and lives to an average of 70+ years, why begrudge them the mere 5-6 years they devote to tending their young families?

Denise Cummins is the author of Good Thinking: Seven Powerful Ideas that Influence the Way We Think, and The Other Side of Psychology: How Experimental Psychologists Find Out About the Way We Think and Act.