Association of cesarean birth with prevalence of functional constipation in toddlers at 3 years of age: results from the Japan Environment and Children’s Study (JECS) oleh Mari Nakamura, Kenta Matsumura, Yoshiko Ohnuma, Taketoshi Yoshida, Akiko Tsuchida, Kei Hamazaki, Hidekuni Inadera, the Japan Environment and Children’s Study Group