Problem: Over 25000 Australian women smoke during pregnancy each year, with risks to mother and baby including miscarriage, pre-eclampsia, placental issues, premature birth, and stillbirth. Background: Carbon Monoxide testing has been introduced in antenatal care settings to help identify smokers and motivate them to quit. Aim: This integrative systematic review aims to take a holistic look at Carbon Monoxide (CO) testing to understand how effective and acceptable this practice is in antenatal care. Methods: PubMed, Scopus and CINAHL were searched for literature relating to pregnant women where CO testing has been used to identify smoking as part of a smoking cessation initiative. The search results were then screened and reviewed independently by two authors. A total of 15 studies were deemed relevant and proceeded to quality appraisal using the Crowe Critical Appraisal Tool. A Narrative Synthesis method was used to present the findings. Discussion: Synthesis resulted in four themes: smoking identification and referral to cessation support, smoking cessation, midwifery usability of CO testing and women's perception of CO testing. Whilst carbon monoxide testing increased the identification and referral to cessation support for pregnant smokers, it did not make an overall difference to smoking cessation rates. Midwives frequently report having too little time to conduct carbon monoxide testing. Findings suggest that women accept the test, but their opinions are under-represented in the existing evidence. Midwives and women report concern for the midwife/woman relationship if testing is not conducted well. Conclusion: Whilst carbon monoxide testing can identify smoking, it does not appear to motivate pregnant smokers to quit.