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A prospective, observational study investigating the use of carbon monoxide screening to identify maternal smoking in a large university hospital in Ireland
  1. Ciara Marie Edel Reynolds1,2,
  2. Brendan Egan2,3,
  3. Rachel AK Kennedy1,
  4. Eimer G O’Malley1,
  5. Sharon R Sheehan1,
  6. Michael J Turner1
  1. 1 UCD Centre for Human Reproduction, Coombe Women and Infants University Hospital, Dublin, Ireland
  2. 2 UCD School of Public Health, Physiotherapy and Sports Science, University College Dublin, Dublin, Ireland
  3. 3 School of Health and Human Performance, Dublin City University, Dublin, Ireland
  1. Correspondence to Miss Ciara Marie Edel Reynolds; ciara.reynolds{at}


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.

  • smoking
  • carbon monoxide
  • screening
  • pregnancy
  • non-disclosure

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See:

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  • Contributors CMER contributed to the conception and design of the study, performed the analysis of the data, interpreted data and wrote and edited this original article. RAKK, EGOM and SRS contributed to the writing and editing of this article. MJT and BE contributed to the conception of the study, interpretation of data as well as contributing to the writing and editing of this article.

  • Funding This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent Obtained.

  • Ethics approval The study was approved by the Research Ethics Committee of Coombe Women and Infants University Hospital (17-2015).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement Additional unpublished data are available. For further details, contact CMER (