In this paper I propose an explanation of the socio-economic differentials in fertility levels and their variation across post-industrial countries. The theoretical framework used is based on social class analysis and the welfare regime approach. I hypothesize that individuals’ social class positions are linked to their levels of economic security, employment-parenthood role compatibility, and gender equality, which are key variables in the explanation of fertility in contemporary post-industrial societies. Different combinations of these variables for each social class and country lead to class specific fertility patterns. I use the French, Italian, Norwegian and British samples of the European Union Statistics on Income and Living Conditions, for the years 2004-2015, and discrete-time event history analysis techniques to analyze second birth probabilities. Results show distinct social class patterns for each country, consistently with the theoretical expectations. Thus, in Norway and France overall high levels of second births probabilities are found, that follow a positive social gradient. In the United Kingdom and Italy a U-shaped relationship between class and second birth probabilities prevails, albeit with different overall levels of fertility. The results show that social class is not only key to understand intra country differentials in fertility, but it is also useful to understand the functioning of the welfare regime and its relationship to overall levels of fertility