Cohort Profile: the Etude Epidémiologique sur les Petits Ages Gestationnels-2 (EPIPAGE-2) preterm birth cohort

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Prematurity has shown an upward trend since 1990, accounting for about 10% of births worldwide, representing almost 15 million babies born every year before 37 weeks’ gestation.1,2 In France, the preterm birth rate was 7.4% in 2010, with about 60 000 babies born preterm every year.3 The burden of preterm birth is substantial: it remains a major cause of child mortality during both the neonatal period and childhood before the age of 5 years.4 Among survivors, the frequency of prematurity-related health problems and developmental deficiencies is substantial, in the short and in the long term after birth.2,5 With prematurity and survival rates both increasing, these ‘individuals born preterm’ represent a growing share of the population, displaying specific health care and support needs. Population-based cohort studies are the methodology of reference for assessing the longitudinal evolution of these fragile infants. Several European and international cohorts have been conducted since the late 1990s, mainly focusing on children born extremely preterm, between 22 and 26 weeks’ gestation.6–9 Only a few studies included infants born very (27–31 weeks) or moderately (32–34 weeks) preterm, although they are more numerous and with a greater impact on public health indicators.10,11 The first EPIPAGE (Etude Épidémiologique sur les Petits Âges Gestationnels) cohort study was launched in 1997 in nine French regions, including births occurring at 22–32 weeks’ gestation, with follow-up steps until age 8 years.12 The cohort provided estimates of mortality, morbidity and disability and health care needs and greatly contributed to changing practices in the neonatal period and after hospital discharge.13,14 Medical practices and the organization of care vary widely across countries and have markedly evolved over the past two decades.15–17 The prognosis of very preterm infants has changed accordingly, raising new questions and requiring new assessments.17 We therefore set up the EPIPAGE-2 cohort, a new longitudinal study of preterm infants, with the following objectives: to provide actualized estimates of short- and long-term outcomes for extremely, very and moderately preterm babies and their families; to study changes in practices at both individual and organizational levels and their impact on child health and development; and to explore aetiologies of preterm birth and identify early predictors of adverse outcomes.17 EPIPAGE-2 is a population-based cohort study, set up in 2011 in 25 regions in France (21 of the 22 metropolitan regions and four overseas regions). Only one region (Poitou-Charentes), accounting for 2.2% of all births in France in 2011, did not participate because of organizational issues. All maternity units and neonatology departments participated in the recruitment (Figure 1). Number of maternity units in the French regions involved in the EPIPAGE-2 cohort study. III, type III maternity unit; II, type II maternity unit. *Including maternity units from Corsica The establishment of the cohort required a close collaboration between the EPOPé research team [National Institute of Health and Medical Research (Inserm U1153), Université de Paris] on the one hand, and a national group of participants from 555 French maternity units, 281 neonatology departments and 39 perinatal networks and parent associations, on the other hand. At a national level, a steering committee, including epidemiologists, paediatricians and obstetricians, was in charge of designing the scientific project and the overall study organization. In each region, a coordinating committee was responsible for implementing the study at the regional level. Local clinical teams from maternity and neonatal units were involved in inclusions and data collection, with the help of regional coordinators. The study relies on several sources of funding, including support from the French National Institute of Public Health Research (IRESP TGIR 2009–01 programme)/Institute of Public Health and its partners [the French Health Ministry, the National Institute of Health and Medical Research (INSERM), the National Institute of Cancer, the National Solidarity Fund for Autonomy (CNSA)], the National Research Agency through the French EQUIPEX program of investments for the future (grant no. ANR-11-EQPX-0038) and the PremUp Foundation. Additional funding was obtained from the Fondation pour la Recherche Medicale (SPF 20160936356) and Fondation de France (00050329 and R18202KK [Grand Prix]). As required by French law and regulations, recruitment and follow-ups were approved by the national data protection authority (Commission Nationale de l’Informatique et des Libertés, CNIL DR-2011–089, DR-2012–246, DR-2013–406, DR-2016–290) and by the appropriate ethics committees, i.e. the advisory committee on the treatment of personal health data for research purposes (Comité Consultatif sur le Traitement de l'Information en matière de Recherche, CCTIRS, reference nos. 10–626, 12–109 and 16–263) and the committee for the protection of people participating in biomedical research (Comité de Protection des Personnes, CPP, reference nos. 2011-A00159-32 and 2016-A0033-48). Recruitment took place in all maternity units of the 25 participating regions during an 8-month period for extremely preterm births (22–26 weeks) and during a 6-month period for very preterm births (27–31 weeks) (Figure 1). A sample of moderately preterm births (32–34 weeks) was recruited during a 5-week period. Further details can be found in the study protocol.17 Eligibility was based on gestational age at birth. Participation in the study was proposed to the parents of all eligible children after they received appropriate information, in the maternity or neonatal unit. During recruitment, regional coordinators visited all maternity units to ensure the identification of all eligible children. Only families who orally agreed to participate were included. The only exclusion criterion was refusal to participate. During the recruitment period, 8400 births were eligible, including terminations of pregnancy, stillbirths and live births, among whom 7804 (93%) were enrolled in the study. Refusal rate at baseline was 7% (n = 596). With ethics committee approval, a small number of basic perinatal data were collected from birth certificates for all eligible births, in order to characterize non-participants. Neonates whose parents refused participation were more frequently born at 32–34 weeks’ gestation and to younger mothers of lower socioeconomic position (SEP) (Table 1). Comparison of participants and non-participants at recruitment and at follow-up invitation ns, non significant. Weighted percentages. Defined as the highest occupational status between current (or former) occupations of the mother and the father, or mother only if living alone, and based on the Classification of Professions and Socioprofessional Categories, developed by the French National Institute of Statistics and Economic Studies. Intermediate socioeconomic position includes employees from administration and public service, self-employed and students. Comparison of participants and non-participants at recruitment and at follow-up invitation ns, non significant. Weighted percentages. Defined as the highest occupational status between current (or former) occupations of the mother and the father, or mother only if living alone, and based on the Classification of Professions and Socioprofessional Categories, developed by the French National Institute of Statistics and Economic Studies. Intermediate socioeconomic position includes employees from administration and public service, self-employed and students. The follow-up was proposed to all families of children discharged alive from hospital (i.e. 4467 children). The families of 155 children (3%) had agreed to participate at baseline but secondarily refused to take part in the follow-up. Thus, 4312 children were eligible for the follow-up. Families who

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