title: A study on the factors affecting the follow-up participation in birth cohorts.
abstract: OBJECTIVE
  A stable follow-up participation rate is a very important factor for validity in a cohort study. This study analyzed the factors that affect the participation rate at one hospital-based birth cohort in South Korean.
  
  
  METHODS
  The participants were recruited from the Mothers' and Children's Environmental Health study between 2006 and 2010. The analysis targeted 1751 mothers who participated in a birth cohort. We conducted analyses of general characteristics during pregnancy and those of infants at birth that affect the participation rate of the 6-month follow-up survey.
  
  
  RESULTS
  The participation rate for the 6-month follow-up survey was 60.4%. The participation rate in the follow-up of the subsequent period decreased within a 5% to 10% range compared to the number of subjects. The participation rate of premature infants was 16.9% lower than that of a full-term infant (52.6% vs. 69.5%). Analysis showed a 16.7% difference between the participation rate of low-birthweight infants in follow-ups (53.7%) and the participation rate of infants with normal weight (70.4%). The participation rate of mothers who were employed during pregnancy was significantly lower for the 6-month follow-up compared to the participation rate of mothers who were unemployed during pregnancy.
  
  
  CONCLUSIONS
  In this study, factors such as premature birth, low-birthweight, and the employment status of the mother during pregnancy affected the participation rate of the follow-up survey for the birth cohort at six months. A specific strategy is needed to encourage survey participation for the high risk groups in the follow-ups.
authors.affiliation: Department of Preventive Medicine, Ewha Womans University School of Medicine, Seoul, Korea.
authors.forename: Bohyun
authors.identifier: 0000-0002-8538-9662
authors.initials: B
authors.lastname: Park
authors.affiliation: Department of Preventive Medicine, Ewha Womans University School of Medicine, Seoul, Korea.
authors.forename: Eun Jeung
authors.identifier: 0000-0002-7698-3424
authors.initials: EJ
authors.lastname: Choi
authors.affiliation: Department of Preventive Medicine, Ewha Womans University School of Medicine, Seoul, Korea.
authors.forename: Eunhee
authors.identifier: 0000-0002-4224-3858
authors.initials: E
authors.lastname: Ha
authors.affiliation: Department of Preventive Medicine, Dankook University College of Medicine, Cheonan, Korea.
authors.forename: Jong Hyuk
authors.identifier: 0000-0002-8661-493X
authors.initials: JH
authors.lastname: Choi
authors.affiliation: Department Occupational and Environmental Medicine, Ulsan University Hospital, Ulsan, Korea.
authors.forename: Yangho
authors.identifier: 0000-0002-6462-0829
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Department of Preventive Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Yun-Chul
authors.identifier: 0000-0001-9010-7271
authors.initials: YC
authors.lastname: Hong
authors.affiliation: Department of Preventive Medicine, Dankook University College of Medicine, Cheonan, Korea.
authors.forename: Mina
authors.identifier: 0000-0003-1011-9446
authors.initials: M
authors.lastname: Ha
authors.affiliation: Department of Preventive Medicine, Ewha Womans University School of Medicine, Seoul, Korea.
authors.forename: Hyesook
authors.identifier: 0000-0002-9359-6522
authors.initials: H
authors.lastname: Park
keywords: Birth cohort; Loss to follow-up; Participation rate