Looking back in time: outcome of a national cohort of very preterm infants born in The Netherlands in 1983
Section snippets
Project on preterm and small for gestational age infants (POPS)
POPS was initiated in the early 1980s as a collaborative effort of the members of the Perinatal Section of the Dutch Pediatric Association. The primary goals of the project were to obtain information on the national incidence of prematurity, possible causative factors of preterm birth, location and type of neonatal care provided, and outcome of very preterm infants at 2 years of age. The study protocol was approved by the Medical Ethics Committees of the participating hospitals and parents gave
Organization of perinatal care
Centralization of perinatal care in the Netherlands was still in its infancy in 1983 [1]. Only 36% of all POPS infants were born in a level 3 hospital, of whom 50% following intrauterine transport. Of the 857 infants born in a level 1 or 2 hospital, 40% was transported to a level 3 hospital after birth. Overall, 61% of the very preterm infants were treated in a perinatal center and 39% were fully taken care of in level 1 or 2 hospitals. Subsequent regionalization of high risk perinatal care has
Neonatal morbidity
The incidence of liveborn infants <32 weeks gestation was 0.63% and of infants <1500 g 0.68% in 1983 [3]. Multiple pregnancy was an important cause of prematurity as 23% of these infants were part of a multiple pregnancy.
The birthweight and gestational age distribution of liveborn infants is shown in Fig. 1. The distribution of infants over birthweight was: 292 (21.8%) infants <1000 g, 805 (60.2%) 1000–1499 g, and 241 (18.0%) ≥1500 g; and the distribution over gestational age: 75 (5.6%) infants
Mortality
In the first year of life, 363 of the 1338 study infants (27.1%) died, but later mortality was also higher than expected (Table 1). Fig. 2 shows the mortality during the first 2 years in relation to gestational age. No infants under 25 weeks of gestation survived and mortality decreased to less than 50% after 26 weeks of gestation. Mortality in infants <26 weeks of gestation was 93 vs. 28% for infants of 26–32 weeks of gestation and gestational age was a better predictor of neonatal mortality
Outcome
The study population has now been followed up for 14 years with a participation rate of 89%. A routine neurological examination was performed in the neonatal period by the attending pediatrician throughout all levels of care. At 2 years of age, corrected for preterm birth, they were examined by their pediatricians [6], [9], [10], [11]. During a home visit 2–6 weeks after their fifth birthday they were assessed extensively by three specially trained pediatricians [12], [13], [14], [15]. At 9–14
Specific groups
Within the POPS cohort subgroups, such as boys [15], children from multiple pregnancy, and children born with severe intrauterine growth retardation (small for gestational age, SGA) [20], experienced more problems during the neonatal period and in later life. The outcome of extremely preterm infants with a birthweight <1000 g was similar to studies conducted in Canada [34] and Switzerland [35].
The male disadvantage was confirmed at the 5-year assessment, when the prevalence of handicaps was
Discussion
One of the major challenges in follow-up studies is the definition of handicap and disability, especially if children are assessed at multiple timepoints by different groups of researchers using various measurements. The reality of the POPS study is that at 2 years of age we asked the 200 pediatricians if the children had no, a mild, or a severe handicap without providing a definition. At 5 years of age the children were investigated by three specially trained pediatricians who used the WHO
Acknowledgements
We thank all participating children and parents and their pediatricians for their enthusiastic cooperation. This work was partially supported by grant R01 HS08385-02 from the National Institutes of Health.
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