Exposure to tobacco smoke and validation of smoking status during pregnancy in the MIREC Study (Lay summary)

Arbuckle TE, Liang CL, Fisher M, Caron NJ, Fraser WD, the MIREC Study Group. Journal of Exposure Science and Environmental Epidemiology 2018 Jan 3. doi: 10.1038/s41370-017-0011-z.

Both cigarette smoking and exposure to second-hand tobacco smoke during pregnancy can lead to adverse effects on the developing fetus including effects on the reproductive, respiratory, cardiovascular and neurological systems.  As part of the pan-Canadian MIREC (Maternal-Infant Research on Environmental Chemicals) Study, nearly 2000 pregnant women provided blood samples which were analysed for cotinine, a by-product of nicotine (a good measure of their exposure to tobacco smoke). In addition, umbilical cord blood and the newborn baby’s first stools were analysed for nicotine by-products.  In questionnaires, the women reported their smoking history and exposure to second-hand smoke.

When asked during the first trimester of pregnancy, 61% of the women reported never smoking, 27% were former smokers, 6% had quit when they found out they were pregnant, and about 6% were currently smoking.  About 42% of the non-smokers reported that they had been exposed to secondhand smoke (SHS).  Younger women, those with less education or with lower household income were more likely to be daily or occasional smokers.

Cotinine was detected in about 50% of the women’s blood samples and about 20% of the baby’s stools.  Levels of cotinine in the umbilical cord blood were higher if the woman smoked, or if she was exposed to second-hand smoke.  If the woman did not smoke but lived in a multiunit dwelling, cotinine was more likely to be measured in her blood, compared to women living in a single home.  Dwelling type was not significantly associated with cotinine levels in the umbilical cord of non-smoking women.

The study found that there was generally good agreement between what the woman reported on her exposure to tobacco and the levels of cotinine in her blood.  However, older women, those with higher education or income, or those born outside Canada tended to under-report their tobacco exposure.