To what extent do differences in fertility (child-bearing) generate inequality? Studies have shown that fertility is associated with women’s labour market trajectories, wealth, children’s school performance, and is strongly correlated within their social networks. We know less about whether such relationships reflect a causal effect of fertility. This project aims to estimate the causal effect of fertility on the outcomes above by using data on outcomes from IVF(in-vitro-fertilization) treatments. We aim to compare women (and their partners) who end up with different number of children because of differential IVF treatment success and follow their labour market outcomes, wealth, their children’s school performance, and how fertility is affected in their social networks. Since we have established in a previous study, using the same data material, that there is a large degree of randomness in the outcome of a given IVF treatment, this method allows us to study the causal effect of fertility. Our data consists of 32,000 couples from the Danish IVF register that we have linked to labour market and school registers. We are able to observe couples that are both successful and unsuccessful in their IVF treatments and follow them (and their children) up to 20 years. Our results can lead to new knowledge about the causal relationship between fertility and inequality and should therefore be of great interest to the international scientific community and to policy-makers.