Introduction: The impact of pregnancy-related health warning labels (HWLs) appearing on cigarette packages on women of reproductive age and other socio-demographic groups is not well understood. The current study analyzes how different age/gender groups respond to pregnancy-related HWLs as compared to non-pregnancy HWLs. Methods: Data were analyzed from four waves of an online longitudinal study with adult smokers aged 18-64 in Australia, Canada, Mexico, and the US. Participants were classified into four dge\gender groups: women 40 and under; men 40 and under; women over 40; men over 40. Participants rated one pregnancy-related and several non-pregnancy related labels on worry, believability, and motivation to quit. Country-specific adjusted linear GEE were estimated regressing ratings for each of the three key outcomes for 1) pregnancy-related HWLs and 2) a rating difference score that subtracted the average ratings of the non-pregnancy warning from the rating of the pregnancy warning. All models adjusted for socio-demographics and Smoking related variables. Results: In Mexico and Australia, where graphic pregnancy-related HWL imagery is used (i.e., premature infant), women of reproductive age reported stronger believability, worry, and quit motivation than all other groups. Results were similar in the US, where text only HWLs are used. In contrast in Canada, where the pregnancy-related HWL imagery features a pregnant woman, ratings were unassociated with gender/age groups. Stronger effects among women of reproductive age were limited to pregnancy HWLs in each country, except Canada. Conclusions: HWLs that depict graphic effects to illustrate smoking-related pregnancy risks appear to be perceived as particularly effective among women of reproductive age. (C) 2016 Elsevier Ltd. All rights reserved.