In The Netherlands perinatal mortality rates exceed the European average. On a second geographic level of comparison, i.e., within The Netherlands, adverse perinatal outcome rates are much higher in the four largest cities (‘G4’, i.e., Amsterdam, Rotterdam, The Hague, Utrecht). Again, on a third level, i.e., within the G4-cities, adverse perinatal outcomes are overrepresented in socially deprived areas on the borough- and neighbourhood level. For long, population factors such as the high age of mothers at first childbirth, the high prevalence of multiple pregnancies (as a consequence of either assisted reproduction or high maternal age), and the increasing prevalence of non-Western pregnant women were held responsible for the high perinatal mortality. However, these explanations were challenged as perinatal mortality remains high in analyses after exclusion of these risk groups. Recent studies have thus addressed the potential role of other factors, in particular healthcare related factors and geographic (e.g., neighbourhood, environment) factors. Healthcare related factors put forward the unique system of Dutch obstetric care with independently practicing community midwives, travel time to hospital13, and organisational characteristics of hospitals. Candidate environmental factors are physical factors (e.g., air pollution and ambient noise pollution17), and aggregate social factors like urban deprivatio.