How smoking during pregnancy affects you and your baby

 

Ob-gyn Robert Welch has helped thousands of women with high-risk pregnancies realize their dreams of a healthy baby. But even after all those successes, there's still one situation that truly scares him: a pregnant woman who can't quit smoking.
"Smoking cigarettes is probably the No. 1 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 swap their habit for a serious disease such as diabetes or high blood pressure.
"I can control those conditions with medications," Welch says. But when a pregnant woman smokes, he says, nothing can protect her baby from danger.

Why is it so dangerous to smoke during pregnancy?

Cigarette smoke contains more than 4,000 chemicals, including truly nasty things like cyanide, lead, and at least 60 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 is good for your baby (you would never add a dollop of lead and cyanide to his strained peaches), two compounds are especially harmful: 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 Doctors' 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 reduce your baby's supply of oxygen. Nicotine chokes off oxygen by narrowing 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, that narrow straw doesn't even hold as much oxygen as it should.

Inside pregnancy: How smoking affects your baby

A fetus is especially sensitive to nicotine, which can penetrate the placenta and harm its growth. See all pregnancy videos

How will smoking affect my baby?

A shortage of oxygen can have devastating effects on your 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 5 1/2 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 outsize effect on your baby's health.
How smoking affects your baby:
Weight and size
On average, a pack-a-day habit during pregnancy will shave about a half-pound from a baby's birth weight. Smoking two packs a day throughout your pregnancy could make your baby a full pound or more lighter. While some women may welcome the prospect of delivering a smaller baby, stunting a baby's growth in the womb can have negative consequences that last a lifetime.

Body and lungs
Undersize babies tend to have underdeveloped bodies. Their lungs may not be ready to work on their own, which means they may spend their first days or weeks attached to a respirator. After they're breathing on their own (or even if they did from the start), these babies may have continuing breathing problems — because of delayed lung development or other adverse effects of nicotine. Children whose mothers smoked during pregnancy are especially vulnerable to asthma, and have double or even triple the risk of sudden infant death syndrome (SIDS). Heart
Babies whose mother smoked in the first trimester of pregnancy are more likely to have a heart defect at birth.
In a U.S. Centers for Disease Control and Prevention (CDC) study published in February 2011, these babies' risk of having certain types of congenital heart defects was 20 to 70 percent higher than it was for babies whose moms didn't smoke. The defects included those that obstruct the flow of blood from the right side of the heart into the lungs (right ventricular outflow tract obstructions) and openings between the upper chambers of the heart (atrial septal defects).
Researchers analyzed data on 2,525 babies who had heart defects at birth and 3,435 healthy babies born in Baltimore and Washington, D.C., between 1981 and 1989.
Brain function
Smoking during pregnancy can have lifelong effects on your baby's brain. Children of pregnant smokers are especially likely to have learning disorders, behavioral problems, and relatively low IQs.
 Children of mothers who smoke during pregnancy may be at increased risk for kidney damage, a new study warns.
Researchers looked at test results for excessive protein in the urine (proteinuria) -- which is a sign of reduced kidney function -- in nearly 44,600 children in Japan who were followed until age 3.
Among the mothers in the study, nearly 5 percent smoked only before pregnancy and about 17 percent of those women continued smoking while pregnant, the study authors said.

Children of mothers who smoked during pregnancy were 1.24 times more likely to show signs of kidney damage than those whose mothers were nonsmokers, the investigators found.
Although the study found an association between smoking during pregnancy and kidney damage in children, it could not prove cause and effect.
"Maternal smoking during pregnancy is known to be associated with preterm birth, low birth weight, and [oxygen deficiency in newborns]. The findings from this study suggest an additional adverse effect of maternal smoking during pregnancy," said study leader Dr. Koji Kawakami. He is a professor and chairman of the department of pharmacoepidemiology at Kyoto University in Japan.
The study was published online Dec. 22 in the Clinical Journal of the American Society of Nephrology.
"Prevention of child proteinuria is important since child proteinuria can lead to development of chronic kidney disease in adulthood and, ultimately, end-stage [kidney] disease," Kawakami said in a journal news release.