Aim One way to assess foetal health of smokers is to ask mothers to count perceived movements, an unreliable method hiding differences in prenatal development. The aim of this pilot study was to assess subtle foetal movements in ultrasound scans and establish whether they differ in foetuses of mothers who smoked and nonsmoking mothers. Methods This longitudinal pilot study recruited twenty mothers (16 nonsmoking; 4 smoking) scanned four times from 24 to 36 weeks gestation (80 ultrasound scans). Two types of fine-grained movements were coded offline and analysed using a Poisson log-linear mixed model. Results Foetuses of smoking mothers showed a significantly higher rate of mouth movements compared to foetuses of nonsmoking mothers (p = 0.02), after controlling for maternal stress and depression. As pregnancy progressed, these differences between the smoking and nonsmoking groups widened. Differences between the two groups in the rate of foetal facial self-touch remained constant as pregnancy progressed and were borderline significant (p = 0.07). Conclusion Rates of foetal mouth movement and facial self-touch differ significantly between smokers and nonsmokers. A larger study is needed to confirm these results and to investigate specific effects, including the interaction of maternal stress and smoking. Additionally, the feasibility of this technique for clinical practice should be assessed.