Rising Illegitimacy Rates - A Query

One often hears that the illegitimacy rate is rising, and I don't doubt it's true. I wonder how much the statistic is concealing, though. Specifically, I'm curious as to how many children are born out of wedlock only to have their parents marry shortly thereafter. A kid whose parents marry a month after she's born is just as illegitimate as one whose parents never marry, though obviously they represent substantially different sociological challenges.