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The Neurobehavioral Legacy of Prenatal Tobacco Exposure |
Research Findings
Vol. 18, No. 6 (February 2004) |
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By Jill Schlabig Williams, NIDA NOTES Contributing Writer More than 17 percent of pregnant women between the ages of 15 and 44 smoke, according to the 2002 National Survey on Drug Use and Health. Much is known about the adverse effects of smoking during pregnancy: Cigarette smoke reduces blood flow through the placenta by as much as 38 percent, and pregnant smokers are more than twice as likely as nonsmokers to have an infant with low birthweight. New research by NIDA-funded investigators now provides the first evidence of toxic effects of prenatal exposure to tobacco smoke on newborn neurobehavior. This finding begins to fill in our picture of how the adverse neurological effects of prenatal exposure manifest from the earliest days of life to later observed effects, including lower IQ and increased risk of developing attention-deficit/hyperactivity disorder. Drs. Barry M. Lester and Karen L. Law and their colleagues at Brown Medical School in Providence, Rhode Island, used the Neonatal Intensive Care Unit Network Neurobehavioral Scale (NNNS) to document the effects of maternal smoking on 1- to 2-day-old infants. The researchers found significant differences in short-term neurobehavioral status in tobacco-exposed newborns compared with unexposed newborns and noted that neurobehavioral impact worsened as the mothers' smoking levels rose. "This study offers the first solid evidence of a dose-response relationship between maternal smoking during pregnancy and newborn neurobehavior," says Dr. Lester. "Babies born to mothers who smoked while pregnant are stressed, which could affect their development." "Focusing on newborn neurobehavioral outcomes is important," comments Dr. Vincent Smeriglio, Chair of NIDA's Child and Adolescent Work Group. "It invites us to think about the continuity of consequences, as we see these very early behavioral differences in prenatally exposed children and consider them in light of effects in older children" (see below, "Cognitive Deficits Persist Into Early Adolescence for Children of Smoking Mothers"). "This research is providing an important piece of the puzzle linking prenatal exposure to cigarette smoke and long-term behavioral outcomes," Dr. Smeriglio says.
The researchers conducted their study with 56 new mothers, ages 18 to 35, and their newborns at a Providence hospital. Recruited shortly after they had given birth, the mothers--27 smokers and 29 nonsmokers--had not used any illegal drugs during their pregnancy and consumed fewer than four alcoholic drinks per month. Mothers who smoked reported smoking fewer than seven cigarettes per day, with tobacco use confirmed by measuring saliva levels of cotinine, the primary metabolite of nicotine. Only healthy newborns whose weights were appropriate to their gestational ages were included in the study; the researchers controlled for birthweight so the effects they found on neurobehavior could not be attributed to the effects of maternal smoking on birthweight. A certified examiner who was unaware of the mother's smoking status administered the NNNS to each newborn within 48 hours of birth. The test examines an infant's neurological state, considering muscle tone, reflexes, and integrity of the central nervous system (CNS); behavior, including attention, arousal, and excitability; and a checklist of 50 items shown by previous research to be markers of stress or--in high-risk babies--of drug withdrawal. Dose-response effects were determined by evaluating the relationship between measures of maternal smoking (cotinine and self-report) and NNNS scores. "Infants exposed to tobacco in the womb showed statistically significant differences that suggest toxic effects of prenatal tobacco exposure on the newborn neurological system," says Dr. Lester. The tobacco-exposed infants were highly aroused and reactive as indicated by the higher excitability and handling scores, and their muscles were more rigid. They also showed signs of stress and drug withdrawal consistent with what has been reported in infants exposed to other drugs. When the total stress/abstinence scores were broken down into subscales, exposed infants showed significant CNS, gastrointestinal, and visual effects. Further, infants prenatally exposed to tobacco required more handling to keep them in a quiet and alert state. "These infants' higher scores in such areas as excitability and arousal reflect that nicotine is a stimulant," says Dr. Lester. The researchers also found consistent dose-response relationships for both the cotinine bioassay results and the self-reports of number of cigarettes smoked per day. "These results indicate that greater exposure to tobacco smoke is related to increasingly negative neurobehavioral effects," he adds, "and that these children may be at increased risk for future neurobehavioral problems." Dr. Lester is currently designing a larger, multisite study focusing on the neurobehavioral effects of prenatal exposure to cigarette smoke. Future research will attempt to pinpoint which components of tobacco are responsible for the known neuro-behavioral effects; determine whether those effects are long-term; clarify whether newborns experience nicotine withdrawal; and separate the effects of prenatal exposure from those of postnatal exposure through second-hand smoke or breastfeeding. With valid information on the potential neurobehavioral effects of prenatal tobacco exposure, more pregnant women may be swayed to quit smoking, notes Dr. Lester. "The smoking effects observed in our study underscore the importance of smoking cessation programs, particularly for women of childbearing age," he says. Source Law, K.L.; Stroud, L.R.; LaGasse, L.L.; Niaura, R.; Liu, J.; Lester, B. Smoking during pregnancy and newborn neurobehavior. Pediatrics 111(6):1318-1323, 2003.
Volume 18, Number 6 (February 2004) |
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