Sociodemographic determinants for initiation and duration of breastfeeding – Polish Mother and Child Cohort Study - Kwarta, Paulina; Polańska, Kinga; Jerzyńska, Joanna; Stelmach, Włodzimierz; Krakowiak, Jan; Karbownik, Michał; Król, Anna; Hanke, Wojciech; Stelmach, Iwona (Pediatria Polska - Polish Journal of Paediatrics, 2018)