The number leading today's New York Times - that most births to American women under 30 occur outside marriage - is a startling one, although it follows on a trend that has been developing for many years. Here are some details:

Once largely limited to poor women and minorities, motherhood without marriage has settled deeply into middle America. The fastest growth in the last two decades has occurred among white women in their 20s who have some college education but no four-year degree, according to Child Trends, a Washington research group that analyzed government data.

Among mothers of all ages, a majority 59 percent in 2009 are married when they have children. But the surge of births outside marriage among younger women nearly two-thirds of children in the United States are born to mothers under 30 is both a symbol of the transforming family and a hint of coming generational change.

One group still largely resists the trend: college graduates, who overwhelmingly marry before having children. That is turning family structure into a new class divide, with the economic and social rewards of marriage increasingly reserved for people with the most education.

Marriage has become a luxury good, said Frank Furstenberg, a sociologist at the University of Pennsylvania.

For the Catholic Church, this suggests that the defense of marriage as an institution should highlight the church's teachings on income inequality, poverty and education.On a more pastoral level, it suggests a need to better communicate the significance of sacramental marriage, especially to couples, with or without children, who are considering whether to marry. The church can be very clear about what it condemns, but not so good at communicating why it believes in marriage. Perhaps there should be retreats and programs for the "pre-engaged," that is, those wrestling with the question of whether to marry.