How smoking during pregnancy affects you and your baby

"Smoking cigarettes is probably the number-one cause of adverse outcomes for babies," says Welch, who's the chairman of the Department of Obstetrics and Gynecology at Providence Hospital in Southfield, Michigan. He's seen the complications far too many times: babies born prematurely, babies born too small, babies who die before they can be born at all. In his view, pregnancies would be safer and babies would be healthier if pregnant smokers could somehow trade in their habit for a serious disease such as diabetes or high blood pressure. "I can control those conditions with medications," he says. But when a pregnant woman smokes, he says, nothing stands between her baby and danger.

Why is it so dangerous to smoke during pregnancy?

Cigarette smoke contains more than 4,000 different chemicals, including truly nasty things like cyanide, lead, and at least 60 different cancer-causing compounds. When you smoke during pregnancy, that toxic brew gets into your bloodstream, your baby's only source of oxygen and nutrients. While none of those 4,000-plus chemicals are really good for a baby (you would never add a dollop of lead and cyanide to his strained peaches), two compounds are especially dangerous: nicotine and carbon monoxide. These two toxins account for almost every smoking-related complication in pregnancy, says ob-gyn James Christmas, director of Maternal Fetal Medicine for Commonwealth Perinatal Associates at Henrico Doctor's Hospital in Richmond, Virginia.

The most serious complications — including stillbirth, premature delivery, and low birth weight — can be chalked up to the fact that nicotine and carbon monoxide work together to cut down on your baby's supply of oxygen. Nicotine chokes off oxygen by narrowing the blood vessels throughout your body, including the ones in the umbilical cord. It's a little like forcing your baby to breathe through a narrow straw. To make matters worse, the red blood cells that carry oxygen start to pick up molecules of carbon monoxide instead. Suddenly, even that narrow straw doesn't hold as much oxygen as it should.

How will smoking affect my baby?

A shortage of oxygen can have devastating effects on a baby's growth and development. On average, smoking during pregnancy doubles the chances that a baby will be born too early or weigh less than 5½ pounds at birth. Smoking also more than doubles the risk of stillbirth.

Every cigarette you smoke increases the risks to your pregnancy. A few cigarettes a day are safer than a whole pack, but the difference isn't as great as you might think. A smoker's body is especially sensitive to the first doses of nicotine each day, and even just one or two cigarettes will significantly tighten blood vessels. That's why even a "light" habit can have an outsized effect on your baby's health.

See how smoking affects your baby's:

Weight and size

On average, a pack-a-day habit during pregnancy will shave about a half-pound from a baby's birth weight. If you smoke two packs a day throughout your pregnancy, your baby might be a full pound or more lighter than he would have been. While some women may welcome the prospect of a smaller baby — especially if they've delivered a 9-pounder in the past — stunting a baby's growth in the womb can have negative consequences that last a lifetime.

Body and lungs

Undersized babies tend to have underdeveloped bodies. As a result, their lungs may not be developed enough to work on their own, which means they may spend their first days or weeks attached to a respirator. Even after they can breathe on their own, their troubles may continue. Children whose mothers smoked during pregnancy are especially vulnerable to asthma later in life. Underdeveloped lungs may also help explain the tragic fact that smoking during pregnancy can double or even triple the risk of sudden infant death syndrome (SIDS).

Brain function

Smoking during pregnancy can have lifelong effects on a baby's brain. Children of pregnant smokers are especially likely to have learning disorders, behavioral problems, and relatively low IQs. Recent animal studies suggest that nicotine in the womb can also program a baby's brain for a future addiction. By the time that baby becomes a teenager, just a few cigarettes could be enough to get him completely hooked.

What can I do?

Behind all these grim statistics lies an incredible opportunity: You can give your baby a huge gift just by giving up your habit — and the sooner the better. Ideally, you should give up smoking before you even conceive. For one thing, you'll have an easier time getting pregnant in the first place. (Smoking cuts the chance of conceiving during any particular cycle by about 40 percent.) You also won't have to struggle with quitting at a time when you should be thinking about other things, like eating well, exercising, and preparing for the big day.

Of course, not everybody manages to plan that far ahead. But if you're still smoking when you discover you're pregnant, you need to immediately start taking steps toward quitting. If you can stop smoking before you're 14 weeks pregnant, you're probably as likely as any other mother to have a healthy, full-sized baby. After weeks 14 to 16, fetuses should be greedily putting on weight. If you're still smoking at that stage, your baby's growth will start to lag. But as soon as you quit, your baby will start getting the oxygen he needs to grow. By the time you have your next ultrasound, the doctor should be able to see a significant change in your baby's growth rate. Even if you're smoking at 30 weeks or beyond, you can still give your baby several weeks to put on weight as quickly as possible. It's as easy — and as difficult — as throwing away your cigarettes and never lighting up again.

Even though you're aware of the dangers of smoking, it's not always easy to give up the habit. The pull of nicotine can be enough to overwhelm all of your good intentions and even override your devotion to your child. That's why you shouldn't try to give up on your own. Talk to your doctor about different ways to quit. Ask your partner and other people around you for support. Use our bulletin board to get help from other expecting moms who've quit. You have to be able to count on other people. After all, there's somebody counting on you.