A two-week-old boy finds his feet in his new world.
A two-week-old boy finds his feet in his new world. - 
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BOB MOON: It's Freakonomics time. It's that time every couple of weeks here on Marketplace where we explore the hidden side of everything. Today: When a new technology is unveiled, sometimes, the unexpected comes along too.

Here's Stephen Dubner.

STEPHEN DUBNER: One day, during a reporting trip to Anhui Province in China, the journalist Mara Hvistendahl visited a family planning office. She saw something strange.

Mara Hvistendahl: They showed me to a room in their office where an ultrasound machine was kept. And there actually was two locks on the door.

It was kept under lock and key, because --

Hvistendahl: In some countries where sex selection has taken off, people see this machine as really a way to ensure them a boy.

Since the introduction of the ultrasound in Asia, in the early 1980s, it's often been used to determine the gender of a fetus -- and, if it's female -- have an abortion. In a part of the world with big populations, these sex selection abortions have had a big, unintended consequence.

Hvistendahl: I mean there are over 160 million females missing from the population in Asia, and to put that in perspective, it's more than the entire female population of the United States.

So, what happens in a world with too many men? For starters, there's more sex-trafficking, more AIDS, and a higher crime rate. In fact, if you want to know the crime rate in a given part of India, one surefire indicator is the gender ratio. The more men, the more crime. Now, the ultrasound machine didn't create these problems, but it did enable them. So, you have to wonder. What's next?

STEPHEN QUAKE: With a blood test where blood is drawn from the arm it's zero risk for the baby, and essentially zero risk for the mom.

That's Dr. Stephen Quake, he's a biophysicist at Stanford. He's developed a new blood test that will screen for genetic abnormalities, like Down syndrome, in a fetus. That's typically done now with amniocentesis, which requires sticking a big needle through a woman's abdomen -- through the uterus, and into the amniotic sack. A blood test would do away with a lot of that risk, the invasiveness and the cause, and it would give parents information earlier in a pregnancy.

QUAKE: The overall goal here I think is to lower stress. Impending parenthood is a very stressful time.

If more people opt for Quake's blood test, then more people would find out earlier on that they have a fetus with a genetic abnormality. So, would we see the end of Down syndrome births? Here's my Freakonomics co-author, economist Steve Levitt.

STEVEN LEVITT: There are many people now who are willing to put in God's hands whether or not they have a Down syndrome child and I think those are the kind of parents who if they have a Down syndrome child will give loving and supportive households. And then there's the set of parents who desperately want to avoid having a Down syndrome child, who cannot handle financially or psychologically the cost that would come with it.

In other words, just because there's an easier test -- doesn't mean everyone will want to use it. Levitt, being an economist, doesn't see this situation as simply a moral decision; he sees it as a "sorting mechanism."

LEVITT: In a world in which there are two different kinds of people, some who welcome Down syndrome children and some who don't, it seems to me that if you have a cheap, easy, safe, reliable test, that that's a perfect sorting mechanism to ensure that in some sense the "right" Down syndrome children get born.

Dr. Quake's blood test is in clinical trials now, and may be on the market this year. So, we'll start to see the outcome sooner, rather than later. What'll it be? That's hard to say. The future is the future.

But don't be surprised if we turn out to be -- surprised. There are a lot of powerful laws in the universe, but the law of unintended consequences may be one of the most powerful.

I'm Stephen Dubner for Marketplace.