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This is MORNING EDITION, from NPR News. Good morning, I'm David Greene.

STEVE INSKEEP, HOST:

And I'm Steve Inskeep. In Your Health on this Monday morning - what scientists are learning about nicotine and pregnancy. Women know that smoking can harm a fetus, so many pregnant smokers are using nicotine gum or patches to help them stay away from cigarettes.

NPR's Jon Hamilton looks at the latest research on whether the approach works, and how nicotine itself may affect a baby in the womb.

JON HAMILTON, BYLINE: Some women who smoke are able to quit before they get pregnant. That's not how things went for Megan Stern.

MEGAN STERN: I smoked heavily for the first seven weeks of my pregnancy because I didn't know I was pregnant. It was an accidental pregnancy, and I found out while I was in the emergency room for another issue.

HAMILTON: Stern, who lives in Massachusetts, was 21 at the time and had been smoking since she was 14.

STERN: I was going through a really rough time in my life; but I knew there was a possibility, at least, that I'd be continuing the pregnancy. So I wanted to quit smoking right away, just to be on the safe side.

HAMILTON: Stern knew that moms who smoke tend to have babies who are smaller, and more likely to have a range of medical problems. Still, she was pretty nervous about trying to quit cold turkey.

STERN: There was a doctor, one of the attending physicians, who suggested that I quit smoking. And I said, I don't know if I can. I want to, but I'm afraid I'll mess up, and I won't be able to do it. And he suggested that I use the patch - and prescribed it for me.

HAMILTON: So Megan Stern joined the growing ranks of women who have used nicotine replacement therapy during pregnancy. There are a lot of them. Each year, more than half a million babies in the U.S. are born to women who smoked while they were pregnant. And surveys show that up to 30 percent of doctors offer nicotine replacement to pregnant women who smoke.

Researchers have widely differing views on whether pregnant smokers should consider nicotine replacement. Ted Slotkin, at Duke, is firmly in the camp that thinks it's not such a great idea.

TED SLOTKIN: Let's first start with, does it work? The answer is not very well, or not at all.

HAMILTON: Slotkin says for a typical smoker, nicotine replacement can double the chance that they will quit. But studies haven't shown that kind of success in pregnant women. Just last year, "The New England Journal of Medicine' published a study of more than 1,000 pregnant smokers in the U.K. Slotkin says all of them got counseling and were asked to wear an adhesive patch on their skin.

SLOTKIN: Some women got nicotine in the patch, and some women got placebo. They saw no difference in the quit rate between the patch and the placebo.

HAMILTON: By the time they gave birth, women who got nicotine were no less likely to be smoking. But earlier in their pregnancies, these women were less likely to smoke. That suggests that even though they didn't quit, both mother and fetus had less exposure to the thousands of chemicals other than nicotine that are found in cigarette smoke. You'd think that would have to be a good thing. And Slotkin says it is - sort of.

SLOTKIN: From the point of view of the mother, it is unequivocal. It's much better that she takes nicotine instead of all the other smoke products 'cause they're going to cause lung cancer and other things. But you know, in this particular case, we need to look at it from the point of view of the fetus.

HAMILTON: And from that perspective, he says, the advantages are less clear. Most of what's known about the effects of nicotine on a fetus has come from studies of animals. Slotkin himself has done a number of nicotine studies looking at rodents, monkeys and even birds. He says he's focused on nicotine because it's the reason people smoke, and because it would be almost impossible to figure out how every single chemical compound in cigarette smoke affects a fetus.

SLOTKIN: The question that we can answer isn't whether all of those other compounds are important - they probably are - but to what extent the effects of nicotine, by itself, can account for what we see in the offspring of smokers. And the answer is, an awful lot of it.

HAMILTON: Slotkin is especially concerned about nicotine's effect on the developing brain. He says animal studies suggest that nicotine could be the reason that women who smoke are more likely to have children with problems including ADHD, and conduct or learning disorders.

Brain development is a delicate process controlled by chemical signals that act a bit like a piano score. Ordinarily, the signals make sure that individual brain cells play the right note at the right time. But Slotkin says nicotine interferes with these chemical signals.

SLOTKIN: It would be the equivalent of trying to play this piano piece, and some clown comes along with a chunk of 2-by-4 and slams a bunch of keys down and holds them down. Now, you can play those keys, but they don't get heard 'cause they are overwhelmed by this continuous signal that's pre-empting the natural signal. That's the way nicotine works on the developing brain.

HAMILTON: Slotkin says a fetal brain can repair the damage when signals are interrupted temporarily. That's why he thinks pregnant smokers who choose nicotine replacement are better off with gum or lozenges or sprays or inhalers. These may be safer because they allow nicotine levels to fall between doses. Slotkin says nicotine levels tend to remain high when moms smoke cigarettes or use a nicotine patch.

SLOTKIN: Smoking, in a way, is unique because it's done continuously, and nicotine patch delivery is done continuously - every day; virtually around the clock, the whole time.

HAMILTON: So gum may be better than a patch. But Slotkin says the best option is no nicotine at all. For some smokers, that's a scary thought. Megan Stern, the Massachusetts mom, says nicotine replacement therapy helped her get through a critical period.

STERN: I used the nicotine patch for - I guess about two months; first a higher dose, then a medium dose, then a lower dose. Then I was done completely, and I had quit smoking. It did work.

HAMILTON: Still, she says if she'd known more about the effects of nicotine, she might not have gone with the patch.

STERN: I was doing the best I could with the information I had at the time. I wanted the best for my baby, and I did what I thought was right.

HAMILTON: A number of researchers still believe nicotine replacement can help pregnant smokers. Cheryl Oncken is a physician and researcher at the University of Connecticut Health Center. She says many of the studies showing that nicotine doesn't work have problems. For example, that big study in the U.K., it turns out only 7 percent of the women who got nicotine patches actually used them for more than a month, the way they were supposed to.

Oncken says her own study of nicotine gum showed a more positive effect.

CHERYL ONCKEN: What we found is that it helped women reduce their smoking, but not actually quit.

HAMILTON: And Oncken says there's evidence that reduction in smoking helped protect the fetus.

STERN: It actually lowered nicotine exposure in our sample; and we had improvements, mainly birth weight and gestational age.

HAMILTON: Oncken says when moms use nicotine replacement and smoke less, their babies are getting lower doses of toxins such as carbon monoxide, which can damage fetal brain cells.

ONCKEN: And there's other things that could be neurotoxic, such as lead. There's arsenic; there's a lot of bad things in cigarettes. So when you look at the whole of it, if you could help somebody quit smoking, it's not just the nicotine, it's many other harmful chemicals.

HAMILTON: Oncken says in her own practice, she first advises pregnant smokers to quit without using nicotine replacement therapy. But if that's not possible, she will consider gum or an inhaler. Oncken says science has yet to provide the answers that pregnant smokers need.

ONCKEN: There's no clear path to follow. So I think in that case, the individual decision has to be between the patient and her health care provider.

HAMILTON: And of course, that was how Megan Stern ended up using a patch while she was pregnant. Her son is 5 and a half now. And Stern says he has some problems with behavior and attention.

STERN: There could be a lot of reasons for that. But I just know that nicotine is a negative thing to experience, and he experienced it all the way up until he was, you know, 4-month-old fetus. That's a pretty long time.

HAMILTON: Still, Stern says she doesn't spend a lot of time second-guessing her decision.

STERN: He's a great little kid. He's really smart, and he's fascinated by all kinds of scientific stuff. He loves to go on nature walks and collect samples. He has a microscope.

HAMILTON: And science may eventually provide better and safer options for moms who smoke. Researchers, including Cheryl Oncken, are studying drugs that help smokers quit without replacing nicotine.

Jon Hamilton, NPR News.

INSKEEP: And that's Your Health for this Monday morning.

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