The U.S. government isn't often called upon to weigh in on the question of how many babies are made. But a new report from the National Center for Health Statistics does sound an alarm about the frequency with which Americans are reproducing.

Citing a 2.9% drop in the national rate of baby-making in 2009, the NCHS warned last week that if this keeps up much longer, we're going to have some pretty big problems down the road. Just take a look at the statistics below:

What's the reason for the declining national birthrate? Two words: The economy.

See the year this trouble began? In 2007, the year the housing market collapsed. It's no coincidence that fewer people made babies around the same time their economic futures turned uncertain. According to John Hopkins sociology professor Andrew Cherlin, about 20% of U.S. women didn't have children at all during the Great Depression, and here in the Great Recession, it's starting to look like deja vu. When people see their futures as less than bright, they're loath to bring new lives into a world turned gloomy.

And while Professor Cherlin assures us that things will perk back up just as soon as they do out on the factory floor, that may not be soon enough to suit everyone.

What's it mean to investors?
A declining birthrate can mean many things to many people. A threat to the stability of Social Security. An argument in favor of relaxing immigration laws. For shareholders, though, it means added risk to their investments.

All other things being equal, 3%-ish annual declines in the birthrate probably equate to a 3% drag on earnings growth at Natus Medical (Nasdaq: BABY), purveyor of equipment for testing the health of newborns. More diversified in their products, disposable diaper companies Procter & Gamble (NYSE: PG) and Kimberly-Clark (NYSE: KMB) will also feel the pinch. Automakers like Ford (NYSE: F), which lean heavily on sales to multichild families to fuel their profits, could find themselves selling more econoboxes and fewer SUVs and minivans.

Then again, all things rarely are equal. As husbands receive pink slips and wives stay in the workforce to ensure a steady paycheck, sales at infant formula purveyor Mead Johnson Nutrition (NYSE: MJN) could buck the trend -- and the prevailing wisdom -- and actually rise. Conversely, companies that clothe our nation's toddlers -- Carter's (NYSE: CRI) and Gymboree (Nasdaq: GYMB) -- could get hit with a double whammy: Fewer sales to clothe new infants; and for those who are born, more hand-me-downs, as cash-strapped parents pinch pennies.

Foolish takeaway
Sorry for killing the mood on last week's market rally, Fools, but that's the way I see it.

Now it's your turn. Take the Foolish Rorschach test. Do you see something different in today's chart? Tell us about it below.

Fool contributor Rich Smith does not own shares of any company named above. Rich is not a licensed economist, but he plays one on the Web. Check out his latest stock recommendations on Motley Fool CAPS. The Fool has a disclosure policy.

Ford Motor is a Motley Fool Stock Advisor selection. Natus Medical is a Motley Fool Hidden Gems recommendation. Kimberly-Clark and Procter & Gamble are Motley Fool Income Investor choices. The Fool owns shares of and has written covered calls on Procter & Gamble. True to its name, The Motley Fool is made up of a motley assortment of writers and analysts, each with a unique perspective; sometimes we agree, sometimes we disagree, but we all believe in the power of learning from each other through our Foolish community.