The paper seeks to identify common features in the fertility patterns of the English-speaking world and provide a model basis for comparison of fertility between countries and over time. Attention is focused on the heterogeneity within the fertility patterns of Australia, Canada, New Zealand, and the United States, similar to that reported earlier for the UK and the Irish Republic. The recent age-specific fertility patterns of these countries display a marked 'bulge' in fertility of women under age 25. A mixture model with two-component: Hadwiger functions provides a suitable fit. The heterogeneity thus suggested is shown to be related to differences in the timing of births by marital status, and its magnitude is related to the proportion of births outside marriage. Additionally, there is some evidence that, in the United States, and to a lesser extent in New Zealand, this heterogeneity in fertility patterns may be explained by ethnic differences in the timing and number of births. [ABSTRACT FROM AUTHOR]