The numbers are starting to add up.

U.S. Senator Rick Santorum blamed abortion for the lack of young workers to pay for Social Security: “Well, a third of of all the young people in America are not in America today because of abortion — because one-in-three pregnancies end in abortion.” If he was right about that, he should consider blaming someone for the recession.

The latest data brief from the National Center for Health Statistics offers the strongest evidence yet that the recession has driven birth rates down.

Here are three ways the evidence points toward the recession decreasing Americans’ production of children. First, the timing: 2009 saw the largest single-year drop in fertility rates since the early 1970s. Here is my graph of annual change in the number of live births per 1,000 women ages 15-44 (sometimes called the “general fertility rate”):

The decline is very broad — affecting all race-ethnic groups, almost all states, and all ages of women (except the oldest). However, I’m taken by a second pattern, which shows the declines steepest at the higher birth orders — so the people who are most affected are those who already have kids, which fits the idea of families embracing the new austerity in place of the old three-is-the-new-two gestalt that seems so mid-2000s now:

I wrote a longer post on this last fall, in which I summarized the argument that this recession was serious business for birth rates:

If you put together busted real estate values and increasing education costs, collapsing state services increasing insecurity, and tightened access to credit, then the resulting “era of thrift” in the culture of consumption might include fewer children among both rich and poor. There is room for such a change, as a very serious “correction” would still only take the U.S. down to the level of its economic peers.

At the time I quoted this 2010 Pew report, which concluded: “Birth rates in the United States began to decline in 2008 after rising to their highest level in two decades, and the decrease appears to be linked to the recession”. In it, the analysts compared home prices and per capita income changes in states with changes in fertility, which showed a consistent pattern of greater birth declines in harder-hit states.

With the new data new birth data by state, and state unemployment rates from the Bureau of Labor Statistics, I can extend that now, and I think it’s a pretty strong third point: fertility fell more where the recession hit harder. The state-level correlation between changing fertility rates in 2007-2009 and changing unemployment rates in 2006-2008 is .48 on a scale of 0 to 1. (I figured it made sense to take unemployment rates from the year previous.) Here is the pattern:

It remains to be seen whether this is a small correction, or even just a delay, in birth rates on account of the economic crisis. Compared with the other rich countries, the U.S. still has high fertility rates. And in the long run that might be a more important issue than the recent fluctuations.