The framework was supported by the literature identified, but more research of sound methodology is needed in order to conclusively disentangle the interplay of the different determinants. Practitioners should be aware that pregnant women who are young, have a low education or do not follow general health advice appear to be at higher risk of inadequate dietary intake.

IntroductionThe heterogeneity among the German population is increasing. Sociodemographic differentials (eg, in education and migrant status) have been associated with health disparities. Life course studies show that a considerable part of these disparities is determined by exposures during pregnancy and early childhood. The BaBi study was established in 2012 to investigate the production of health disparities from foetal life to childhood in the city of Bielefeld, Germany.Methods and analysisBetween 2013 and 2016, detailed information on socioeconomic characteristics, migration background, lifestyle factors, environmental factors, healthcare use, and health status of 995 newborns, including 24 twins, and their families was collected using standardised instruments. Data collection started during pregnancy or shortly after birth with a computer-assisted personal interview of the pregnant woman/mother. Follow-up data will be collected until 2018 by computer-assisted telephone interviews around the first, second and after the third birthday of the child and by linking routine healthcare data. Blood samples are collected from a small subsample of 50 mothers for a substudy about stress during pregnancy (BaBi-Stress study).Ethics and disseminationThe study was approved by the ethical committee of the Medical Faculty of Muenster University and the Data Protection Board of Bielefeld University. Results will be published in scientific journals. Data sets and questionnaires will be made accessible for researchers based on access proposals and data usage contracts.

The majority of European birth cohorts assessed participants' migration history or ethnic background; however, this information was seldom used for comparative analyses in trying to disentangle reasons for health inequalities. Also, heterogeneous indicators were used. Better use of data already available, as well as harmonization of data collection on migration history and ethnicity, could yield interesting insights into the production of health inequalities.

For recruitment of women with a migration background, it is crucial to use both careful preparation in the form of qualitative measures (focus groups, structured interviews) and a pilot study. Extra resources should be planned from the beginning for diverse recruitment strategies and a higher personnel demand (e. g., for translations and back translations). Efforts for the inclusions of migrants in social epidemiological studies in Germany should be a routine process.

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