If nearly half of U.S. pregnancies are unplanned, then how can the economy alone be blamed for the recent decline in births? Maybe a bad economy is so sobering for Americans that they become more careful in their sexual activity, so that there are fewer planned and unplanned births. Or maybe the depression of losing jobs and money just results in less sex. But it is also possible that more than just the economy is at work.

That was the counterpoint reaction I gained overnight from Wendy Hellerstedt, an associate professor at the University of Minnesota School of Public Health, to news reports about the economy prompting another annual decline in U.S. births from 2010 to 2011. Minnesota mirrored the national trend, with an annual decline in births in 2011 that was much smaller than the declines in the prior three years.

Hellerstedt studies the relationships between social indicators and reproductive health. She didn't dismiss the economic impact, but said it is probably only one of several factors. Globally, a decline in births is more often tied to gains in education and job opportunities for women, she said. A key is knowing whether new mothers intended to get pregnant or not: