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Table 2 Descriptive statistics

From: Use of hospital-based health care services among children aged 1 through 9 years who were born very preterm - a population-based study

Measure   Statistics Person- years of observation
  Number of VPT Children 5587 13,915
  Mean (sd) Birth year 2005 (2.6) 13,915
Sex # (%) Boy 2881 (51.6%) 7136
Gestational age # (%) 22–24 weeks GA 198 (3.7%) 495
  # (%) 25–26 weeks GA 533 (9.9%) 1335
  # (%) 27–28 weeks GA 1029 (19.1%) 2565
  # (%) 29–30 weeks GA 1716 (31.8%) 4298
  # (%) 31+ weeks GA 1922 (35.6%) 4725
  # (%) Missing GAa 189 (3.4%) 498
Birth weight Mean (sd) Birth weight 1275.6 (378.8) 13,592
  # (%) Missing birth weigha 115 (2.1%) 323
  # (%) Small weight for GA 1575 (29.2%) 3875
  # (%) Missing weight for GAa 201 (3.6%) 534
Malformation at birth # (%) Has Q-diagnosis 1183 (21.2%) 2903
Apgar score at 5 min Mean (sd) Apgar score 5 min 8.3 (1.7) 13,592
  # (%) Missing Apgar score 5 mina 80 (1.4%) 323
Multiple birth # (%) Multiple birth 1658 (29.7%) 4151
  # (%) First in multiple birth 4718 (84.4%) 11,726
Parity # (%) No previous children 2972 (55.3%) 7268
  # (%) 1 previous child 2405 (44.7%) 6042
  # (%) Missing parity 210 (3.8%) 605
Age of mother Mean (sd) 30.5 (5.5) 13,915
Health status of mother # (%) Chronic hypertension 124 (2.2%) 302
  # (%) Bleeding any time in pregnancy 798 (14.3%) 1937
  # (%) Hellp syndrome 197 (3.5%) 500
  # (%) Any previous abortion 1323 (23.7%) 3296
Highest education # (%) Primary school 851 (17.9%) 2199
among maternal grandparents # (%) Secondary education 2765 (58.1%) 6937
  # (%) University education 1139 (24.0%) 2824
  # (%) Missing grandparents education levela 832 (14.9%) 1955
Immigration status # (%) Non-Norwegian native 935 (16.7%) 2184
Civil status (at birth) # (%) Single/separated/divorced 525 (9.5%) 1218
  # (%) Married/Cohabiting 4994 (90.5%) 12,521
  # (%) Missing civil statusa 68 (1.2%) 175
Mothers’ education # (%) Primary school 1265 (24.7%) 3159
(2 years before birth) # (%) Secondary education 1949 (38.1%) 4982
  # (%) University education 1908 (37.3%) 4678
  # (%) Missing educationa 465 (8.3%) 1096
Income (1 year before birth) Mean (sd) in thousands 290.4 (205.7) 13,424
  # (%) Missing incomea 206 (3.7%) 491
Age of father (at birth) Mean (sd) 33.5 (6.7) 13,703
  # (%) Missing age of fathera 92 (1.6%) 212
Geography (at birth) Mean (sd) Travel time to hospital 24.9 (32.5) 13,915
Hospital region (at birth) # (%) South-Eastern health authority 3059 (54.8%) 7581
  # (%) Western health authority 1254 (22.4%) 3098
  # (%) Central health authority 754 (13.5%) 1930
  # (%) Northern health authority 520 (9.3%) 1307
  1. VPT very preterm, sd standard deviation, GA gestational age
  2. Numbers in column ‘Statistics’ shows means and standard deviations (sd) for continuous variables, and the number of observations (#) and percentages (%) for categorical variables and non-missing observations
  3. aFor variables with missing values the number # and percentages (%) out of 5587 VPT children is shown. Person-years of observation is in the period 2008-2010