Page 46 - Sample Moderate prematurity, socioeconomic status, and neurodevelopment in early childhood

Chapter 4
METHODS
Study design
This study is part of the Longitudinal Preterm Outcome Project (LOLLIPOP), a Dutch prospective cohort study designed to investigate growth, development, and general health of preterm-born children, with particular attention to MP children born at 320 to 356 weeks of gestation.17 LOLLIPOP consists of a community-based sample of preterm children and a matched random sample of term-born controls (380 to 416 weeks of gestation). The 4-year-old participants were recruited from 13 randomly selected preventive child health care (PCH) centres across the Netherlands, covering urban and rural areas. Together these centres covered the care for 45,446 children, representing 25% of all 4-year-olds monitored by Dutch PCH centres. In the Netherlands, 90% to 95% of children are seen regularly and free of charge by PCH professionals for well-child care from birth up to 4 years of age.18 PCH professionals, i.e. doctors and nurses, monitor mental and physical development through structured interviews with parents, general physical examinations, and standardised screening procedures, all of which are documented in PCH files. The study was approved by the review board of the University Medical Center Groningen, and written informed consent was obtained from the parents of study participants.
Sampling procedure
MP children were sampled from a community-based cohort of 45,455 children born in 2002 and 2003. We based the size of the sample on estimates of the numbers needed to compile growth curves for Dutch preterm-born children, because for that part of the LOLLIPOP study we needed the largest number of children. Each of the 13 PCH centres provided a sample of preterm children and term-born controls of the same age-range, based on their card files. After the file of each second preterm child had been selected, the file of the next term-born child served as a control. Children were excluded if they had congenital malformations or syndromes, if the gestational age could not be verified or was beyond of the set range, or if families had moved between sampling and inclusion. An overview of the sampling procedure of LOLLIPOP was previously provided.17 In short, out of 1145 eligible MP children, 995 parents (86.9%) agreed to participate in the long- term follow-up part of the study, and of the 674 eligible term-born children, 577 (85.6%) parents agreed to participate. Response rates among parents of the fully
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