Growing Up in Hungary is a birth cohort study, meaning that it studies children born within the same time period (2018/19), consisting of a joint cohort (generation). We defined the theoretical population of the study as children born in Hungary within a one-year period between April 1, 2018 and April 30, 2019 and their families. The size of the total population is about 90,000 children, and the initial number of sample units is approx. 9,000 pregnant women.
Since the local health visitors are the ones recruiting the pregnant women to participate and conducting the first two data collections, we chose the health visitor districts as our primary sampling units. The initial sample included 600 health visitor districts, from where the mothers and their future-born children represent the entire target group of our analysis of the country on a small scale, ensuring that the research is representative, and generalizations can be made from the results gained. We invited each pregnant woman under prenatal care in these districts to participate if her child was expected to be born within the specified time period.