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Objectives: This study evaluated breath carbon monoxide (BCO) testing in identifying maternal smokers as well as the difference between disclosers and non-disclosers of smoking status. We also investigated if other extrinsic factors affected the women's BCO levels in pregnancy., Design: A prospective observational study., Setting: A university obstetric hospital in an urban setting in Ireland., Participants: Women (n=250) and their partners (n=54) were recruited at their first antenatal visit. Women <18 years and those who did not understand English were excluded. A booking history, including recording of smoking status, was collected by midwives. Following this, women were recruited and completed a detailed research questionnaire on smoking and extrinsic/environmental BCO sources. A BCO test was performed on both the woman and her partner., Primary and Secondary Outcome Measures: The number of self-reported smokers and those that were positive on the BCO test. The characteristics of women who disclosed and did not disclose smoking status. The effect of extrinsic factors on the BCO test results., Results: Based on the receiver-operating characteristic curve, a BCO cut-off point of ≥3 ppm was the optimal level to identify ongoing smoking. At booking history, 15% of women reported as current smokers. Based on BCO levels ≥3 ppm combined with self-reported smoking in the research questionnaire, the rate increased to 25%. Non-disclosers had similar characteristics to non-smokers. No extrinsic factors affected maternal BCO levels., Conclusions: Based on self-report and BCO levels, a quarter of women presenting for antenatal care continued to smoke, but only 60% reported their smoking to midwives. BCO measurement is an inexpensive, practical method of improving identification of maternal smoking, and it was not effected by extrinsic sources of BCO. Improved identification means more smokers can be supported to stop smoking in early pregnancy potentially improving the short-term and long-term health of both mother and child., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2018. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Objectives: Using detailed dietary and supplement questionnaires in early pregnancy, we compared the dietary intakes of micronutrients and macronutrients at the first prenatal visit of women who reported continuing to smoke during pregnancy with the intakes of women who were non-smokers., Design: Cross-sectional study conducted between June 2014 and March 2016., Setting: Stand-alone tertiary maternity hospital in an urban setting with approximately 8000 deliveries per year., Participants: Women were recruited at their convenience after sonographic confirmation of an ongoing singleton pregnancy (n=502). Detailed dietary and supplement information was available for 398 women. Women <18 years and those who did not speak English fluently were excluded., Primary and Secondary Outcome Measures: The differences in dietary micronutrients and macronutrients and maternal folate levels between women who continued to smoke in pregnancy compared with non-smokers., Results: Of the 502 women, the mean age was 30.5 (SD 5.6) years, 42.5% were nulliparas, 19.2% were obese and 398 (79.3%) completed the questionnaire satisfactorily. In the 50 (12.6%) current smokers, the micronutrients magnesium, iron, carotene and copper were lower (all p<0.005) whereas sodium and chloride were higher compared with the 348 (87.4%) non-smokers. Smokers reported lower intakes of dietary total folate (p=0.006) compared with non-smokers (i.e., dietary folate equivalents; intake from natural and fortified dietary sources) (p=0.005). Smokers also reported lower intakes of fibre than non-smokers (13.1 g (IQR 7.7) vs 16.3 g (IQR 8.5), p<0.001). The dietary intakes of former smokers compared favourably with non-smokers., Conclusions: We found that women who continue to smoke during pregnancy have serious dietary inadequacies which could potentially aggravate fetal growth restriction associated with direct toxicity from cigarettes. This provides a further reason to promote smoking cessation interventions in pregnancy, and highlights the need for dietary and supplementation interventions in women who continue to smoke., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2018. Re-use permitted under CC BY. Published by BMJ.)