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Comparison between Self-Report and Biochemical Assessment of Smoking in Pregnancy

Triche, E W.; Belanger, K; Hellenbrand, K; Leaderer, B P.; Bracken, M B.

ISEE/ISEA 2006 Conference Abstracts Supplement: Symposium Abstracts: Abstracts

Department of Epidemiology and Public Health, Yale School of Medicine, New Haven, Connecticut


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Having reliable data on important in utero exposures such as smoking has important implications for short-term (eg, perinatal) and longer-term (eg, childhood and adulthood) outcomes. One recently completed cohort study allows us to examine the reliability of self-report data of in utero exposure to tobacco. If biochemical verification is found necessary, then exposures must be assessed during pregnancy.

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The Nutrition in Pregnancy study (NIP) screened over 11,000 women early in pregnancy and enrolled 2478 women with various levels of self-reported tobacco consumption. Women gave informed consent before enrollment. At enrollment interview (<24 weeks gestation), women were asked detailed questions about smoking exposures in early pregnancy. At the same visit, we collected urine samples, which were analyzed for cotinine, nicotine, and creatinine concentrations. Self-report and biochemical measures of tobacco exposure were compared.

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One hundred ninety-three women had levels of urinary cotinine >80 ng/mL, a level that indicates active smoking (Smoke-Free Families project). According to interviews, only 169 women reported active smoking in the prior day, 153 women reported smoking in the third month of pregnancy, and 273 reported smoking at some point since the pregnancy began. Of the 193 smokers identified by cotinine, 29 (15%) reported not smoking “yesterday.” Of the 29 women, 13 reported no passive smoke exposure on the previous day. Although biochemical verification may identify women who misrepresent their smoking status, it is only valid for a 7-day window (SRNT Workgroup); thus, this measure may not reflect exposures at different times in pregnancy. In our data, of 273 women who reported smoking at some time before being interviewed, only 191 (70.0%) had urinary cotinine levels >80 ng/mL at the interview. One hundred of 273 women (37%) reporting smoking in the first trimester had cotinine levels ≤80 ng/mL. Analysis comparing self-report with biochemical measurement of other exposures assessed at different points during the pregnancy and immediately postpartum is underway.

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Self-reported exposure during the perinatal period may be inaccurate, particularly for exposures such as smoking during pregnancy when there is strong social and personal pressure to quit. For primary assessment of these exposures, biochemical verification may be important. However, biochemical measures are subject to different problems, including being valid for only a short window of time.

© 2006 Lippincott Williams & Wilkins, Inc.