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Table 1 Characteristics of the study population presented as count (sample size), median (5th-95th percentile: pregnancy duration, birth weight), or percentage (gender, season at birth, age at heel prick, laboratory)

From: Neonatal heel prick screening TSH concentration in the Netherlands as indicator of iodine status

N   total population nTSH subpopulation
1,435,600   264,407  
Gender (%) male 51 χ2 = 1017, 1 d.f., p < 0.0001 59 χ2 = 9074, 1 d.f., p < 0.0001
Season at birth (%) spring 24 χ2 = 2850, 3 d.f., p < 0.0001 24 χ2 = 826, 3 d.f., p < 0.0001
summer 24 24
autumn 27 27
winter 25 25
Age at heel prick (%) day 3 8 χ2 = 1,007,684, 4 d.f., p < 0.0001 7 χ2 = 148,329, 4 d.f., p < 0.0001
day 4 50 46
day 5 24 24
day 6 15 19
day 7 3 4
Laboratory (%) Amsterdam 20 χ2 = 34,673, 4 d.f., p < 0.0001 20 χ2 = 6307, 4 d.f., p < 0.0001
Bilthoven 21 21
Capelle 25 25
Tilburg 17 17
Zwolle 17 17
Pregnancy duration (days)   280 (262-292)   277 (260-291)  
Birth weight (kg)   3.5 (2.8-4.3)   3.4 (2.7-4.2)