By Cole Petrochko, Staff Writer, MedPage Today Note that these two studies demonstrate an association between maternal smoking during pregnancy and adverse outcomes in adolescents -- in one case hearing loss, and in the other addictive behaviors.Be aware that there are likely multiple unmeasured confounders present in these studies -- a causal link between nicotine expsure in utero and these outcomes will require much more detailed study.Maternal smoking during pregnancy was associated with hearing loss and an increased risk for substance abuse and addiction in the child, two studies showed.
Children exposed to smoke in utero had a nearly threefold risk of unilateral low-frequency sensorineural hearing loss compared with those who were not exposed (aOR 2.6, 95% CI 1.1-6.4), according to Michael Weitzman, MD, of the New York University School of Medicine in New York City, and colleagues in JAMA Otolaryngology Head and Neck Surgery.
Prenatal smoke exposure was also significantly associated with weaker response during reward anticipation (P<0.001) than was seen in those who did not have prenatal smoke exposure, wrote Michael Smolka, MD, of Technische Univeritat Dresden in Germany, and colleagues online in JAMA Psychiatry.
Prior research has shown an association between smoking and secondhand smoke with sensorineural hearing loss in children and adults, as well as higher rates of substance use and dependence among children of mothers who had smoked while pregnant. Additionally, prenatal nicotine exposure has shown altered development of brain areas tied to reward processing in animal models.
Smoking and Hearing Loss
In the New York study, Weitzman and colleagues looked at associations between prenatal smoking exposure to sensorineural hearing loss through cross-sectional data from 964 children and teens ages 12 to 15.
Data were extracted from the National Health and Nutrition Examination Survey (NHANES) 2005-2006 on maternal smoking during pregnancy, secondhand smoke exposure, confounders, and audiometric testing.
Smoke exposure was confirmed via a question asking whether the participant's mother smoked while pregnant with her child. Mothers who said they had smoked were also asked if they had stopped smoking while pregnant and, if they had, at what stage of the pregnancy.
Participant secondhand smoke exposure and active smoking were recorded through self-report and cotinine levels. Cotinine is a metabolite of nicotine.
The authors also measured hearing loss through pure-tone hearing threshold, tympanogram, and otoscopic examination.
The sample included 155 adolescents with mothers who had smoked during pregnancy. Among those mothers, 61.9% said they had smoked during the first trimester, 27.7% during the second trimester, 8.4% during the third trimester, and 1.9% did not recall for how long they smoked.
The authors found that -- across all frequencies -- mean pure-tone hearing level was elevated in children whose mothers smoked during pregnancy compared with those who didn't, and significantly so at 6 kHz for the average of the right and left ears, and at 2 and 6 kHz for the ear with worse hearing (P<0.05 for all).
Among types of hearing loss, unilateral low frequency hearing loss -- but not other types -- was significantly elevated among those with prenatal smoke exposure (P=0.03), and exposure represented a 2.6-fold increased odds of unilateral low-frequency sensorineural hearing loss.
Smoking and Substance Abuse
The study by Smolka and co-authors sampled prenatal cigarette exposure in 177 European adolescents and compared reward response through an fMRI with that of 177 control adolescents who were not exposed to cigarette smoke in utero.
Exposure was assessed through a retroactive questionnaire given to parents, which included smoking status and number of cigarettes smoked per day per trimester.
Participants were screened for psychiatric disorders and attention deficit hyperactivity disorder. They were also assessed for substance use via questionnaire.
Reward response was measured through a modified Monetary Incentive Delay task, which required participants to view a cue presentation, endure an anticipatory delay, respond to a cue, and be scored based on correct response to cue and timing.
Imaging data looked at anticipation of any reward -- small and large -- versus no reward and the effects of a win versus no-win in a trial with a reward. Data were derived from output in the ventral striatum.
Those whose mothers smoked while they were pregnant had a significantly greater lifetime frequency of cigarette smoking themselves, had smoked one or more cigarettes in their lifetime, and were more likely to score positive for neuroticism (P=0.02 for all) versus those whose mothers had not smoked while pregnant.
Exposed participants also had significantly lower scores for impulsivity (P<0.001) and agreeableness (P=0.01).
Following fMRI, those who were born to mothers who smoked during pregnancy showed a weaker response in the left and right ventral striatum (P<0.001 for both), although "response of the ventral striatum to the feedback of a reward did not differ between groups."
The researchers concluded that structural alterations and "lower levels of dopamine release within the ventral striatum after prenatal nicotine exposure" showed attenuated response to the anticipation of a reward, which "may have serious consequences" and mean that those exposed to prenatal smoking are "more likely to engage in risky behavior," based on prior research in those with depressed ventral striatum response to reward.
Weitzman and co-authors said their study was limited by small sample size of the cohort, potential changes in socioeconomic status after the baseline data were recorded, and missing data on other possible sources of smoking exposure. They were also limited by other unmeasured confounders for hearing loss, cross-sectional measure of NHANES, and lack of determination of onset and progress of hearing loss.
Smolka and colleagues noted their study was limited by differences between groups by adolescents' smoking behavior and lack of causal link. The study was also limited by study alterations in the Monetary Incentive Delay task.
Both research teams noted their measurement of maternal smoking through self report was a potential limitation.
Weitzman and colleagues declared no conflicts of interest.
Smolka and colleagues' study was funded by the IMAGEN project, the Alzheimer's Disease, Alcoholism, and Memory project, the European Union Innovative Medicine Initiative AIMS, the Swedish Funding Agency FORMAS, the German Ministry of Education and Research, and Deutsche Forschungsgemeinschaft.
They received support from Bristol-Myers Squibb, Develco Pharma, Lilly, Medice, Novartis, Shire, Viforpharma, Janssen McNeil, and General Electric.
Cole Petrochko
Staff Writer
Cole Petrochko started his journalism career at MedPage Today in 2009, after graduating from New York University with B.A.s in Journalism and Psychology. When not writing for MedPage Today, he blogs about nerd culture, designs websites, and buys and sells collectible card game cards. He is based out of MedPage Today's Little Falls, N.J. Headquarters.
Yeah, we get jealous when we see the Madonnas and the Victoria Beckhams and the Jessica Albas of the world go from pregnant back to size 0 in what seems like a matter of hours. 
