Background
Methods
Study population and definitions
Birth year | Number of unique children entering into study | Follow-up in 2008-2010 | ||||
---|---|---|---|---|---|---|
2001 | 650 | |||||
Age interval | 6/7 | 7/8 | 8/9 | 9/10 | ||
Person-years | 318 | 648 | 648 | 327 | ||
2002 | 634 | |||||
Age interval | 5/6 | 6/7 | 7/8 | 8/9 | ||
Person-years | 313 | 630 | 629 | 318 | ||
2003 | 645 | |||||
Age interval | 4/5 | 5/6 | 6/7 | 7/8 | ||
Person-years | 323 | 643 | 641 | 317 | ||
2004 | 609 | |||||
Age interval | 3/4 | 4/5 | 5/6 | 6/7 | ||
Person-years | 302 | 607 | 606 | 302 | ||
2005 | 606 | |||||
Age interval | 2/3 | 3/4 | 4/5 | 5/6 | ||
Person-years | 292 | 606 | 604 | 312 | ||
2006 | 575 | |||||
Age interval | 1/2 | 2/3 | 3/4 | 4/5 | ||
Person-years | 285 | 571 | 568 | 284 | ||
2007 | 650 | |||||
Age interval | 1/2 | 2/3 | 3/4 | |||
Person-years | 651 | 643 | 314 | |||
2008 | 611 | |||||
Age interval | 1/2 | 2/3 | ||||
Person-years | 612 | 303 | ||||
2009 | 607 | |||||
Age interval | 1/2 | |||||
Person-years | 297 |
Data
Statistical analysis
Missing data
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 |
Results
Descriptive statistics of study cohort
General population comparison
Age- and GA-specific rates
Regression results
Age 1–4 | Age 5–9 | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
(n = 4301) | (n = 3137) | |||||||||
Hospital admissions | IRR | S.E. | P** | z | 95%CI | IRR | S.E. | P** | z | 95%CI |
Boy (vs girl) |
1.22
|
0.10
|
0.014
|
2.47
|
1.04–1.44
|
1.38
|
0.19
|
0.017
|
2.38
|
1.06–1.80
|
22–24 weeks GA (vs 31+) |
2.60
|
0.58
|
<0.001
|
4.28
|
1.68–4.03
|
2.34
|
0.75
|
0.008
|
2.67
|
1.25–4.37
|
25–26 weeks GA (vs 31+) |
1.79
|
0.25
|
<0.001
|
4.22
|
1.37–2.35
|
1.52
|
0.35
|
0.070
|
1.81
|
0.97–2.39
|
27–28 weeks GA (vs 31+) |
1.38
|
0.16
|
0.007
|
2.69
|
1.09–1.74
|
1.51
|
0.31
|
0.046
|
1.99
|
1.01–2.27
|
29–30 weeks GA (vs 31+) |
1.41
|
0.15
|
0.002
|
3.15
|
1.14–1.74
| 1.04 | 0.21 | 0.836 | 0.21 | 0.70–1.54 |
Small weight for GA (vs non-SWGA) |
1.87
|
0.17
|
<0.001
|
6.84
|
1.56–2.24
| 1.15 | 0.18 | 0.384 | 0.87 | 0.84–1.57 |
Malformation at birth (vs absence) |
2.16
|
0.19
|
<0.001
|
8.52
|
1.81–2.57
|
1.55
|
0.22
|
0.002
|
3.04
|
1.17–2.05
|
Apgar score at 5 min (difference from score 9)* |
0.93
|
0.02
|
0.001
|
−3.40
|
0.89–0.97
| 0.94 | 0.05 | 0.187 | −1.32 | 0.85–1.03 |
Parous (vs non-parous) | 1.18 | 0.10 | 0.056 | 1.91 | 1.00–1.40 | 0.76 | 0.11 | 0.053 | −1.93 | 0.58–1.00 |
Age of mother at birth (per 5 years from avg.)* |
0.91
|
0.03
|
0.010
|
−2.56
|
0.85–0.98
| 1.03 | 0.06 | 0.579 | 0.55 | 0.92–1.16 |
Bleeding any time in pregnancy (vs none) |
1.31
|
0.14
|
0.012
|
2.51
|
1.06–1.63
| 1.11 | 0.21 | 0.581 | 0.55 | 0.76–1.62 |
Any previous abortion up to 23rd week (vs none) |
1.27
|
0.12
|
0.010
|
2.58
|
1.06–1.52
| 1.12 | 0.17 | 0.450 | 0.75 | 0.83–1.51 |
University education grandparents (vs < university) | 1.12 | 0.11 | 0.259 | 1.13 | 0.92–1.36 |
0.72
|
0.12
|
0.042
|
−2.03
|
0.53–0.99
|
Mother is immigrant (vs native) | 0.99 | 0.11 | 0.907 | −0.12 | 0.79–1.23 | 0.97 | 0.18 | 0.882 | −0.15 | 0.68–1.40 |
Single/separated/divorced (vs cohabiting/married) | 0.84 | 0.11 | 0.176 | −1.35 | 0.66–1.08 | 0.54 | 0.21 | 0.103 | −1.63 | 0.25–1.13 |
Travel time hospital at birth (per 30 min from avg.)* | 1.02 | 0.05 | 0.713 | 0.37 | 0.93–1.11 | 1.02 | 0.06 | 0.723 | 0.36 | 0.91–1.14 |
Western health authority (vs South-Eastern) |
0.73
|
0.08
|
0.002
|
−3.08
|
0.59–0.89
| 0.95 | 0.19 | 0.807 | −0.24 | 0.64–1.41 |
Central health authority (vs South-Eastern) | 0.94 | 0.10 | 0.603 | −0.52 | 0.76–1.17 | 1.10 | 0.22 | 0.642 | 0.46 | 0.74–1.62 |
Northern health authority (vs South-Eastern) | 0.82 | 0.11 | 0.157 | −1.42 | 0.62–1.08 |
1.72
|
0.37
|
0.011
|
2.54
|
1.13–2.62
|
Reference* rate per 1000 children per year |
181
|
44
|
<0.001
|
21
|
112–293
|
60
|
22
|
<0.001
|
11
|
29–123
|
Outpatient visits | IRR | S.E. | P** | z | 95%CI | IRR | S.E | P** | z | 95%CI |
Boy (vs girl) |
1.15
|
0.06
|
0.015
|
2.43
|
1.03–1.28
|
1.28
|
0.10
|
0.001
|
3.34
|
1.11–1.48
|
22–24 weeks GA (vs 31+) |
3.12
|
0.44
|
<0.001
|
8.16
|
2.37–4.10
|
3.13
|
0.52
|
<0.001
|
6.82
|
2.26–4.35
|
25–26 weeks GA (vs 31+) |
1.89
|
0.18
|
<0.001
|
6.72
|
1.57–2.27
|
2.05
|
0.27
|
<0.001
|
5.52
|
1.59–2.65
|
27–28 weeks GA (vs 31+) |
1.68
|
0.14
|
<0.001
|
6.16
|
1.42–1.98
|
1.79
|
0.19
|
<0.001
|
5.43
|
1.45–2.20
|
29–30 weeks GA (vs 31+) |
1.34
|
0.11
|
<0.001
|
3.65
|
1.15–1.57
|
1.31
|
0.14
|
0.011
|
2.54
|
1.06–1.62
|
Small weight for GA (vs non-SWGA) |
1.50
|
0.09
|
<0.001
|
6.59
|
1.33–1.69
|
1.28
|
0.10
|
0.002
|
3.08
|
1.09–1.50
|
Malformation at birth (vs absence) |
1.57
|
0.10
|
<0.001
|
7.18
|
1.39–1.77
|
1.53
|
0.13
|
<0.001
|
5.03
|
1.30–1.81
|
Apgar score at 5 min (difference from score 9)* |
0.93
|
0.01
|
<0.001
|
−4.28
|
0.91–0.96
|
0.94
|
0.03
|
0.018
|
−2.36
|
0.89–0.99
|
Parous (vs non-parous) | 1.02 | 0.06 | 0.793 | 0.26 | 0.90–1.15 | 0.93 | 0.08 | 0.348 | −0.94 | 0.79–1.09 |
Age of mother at birth (per 5 years from avg.)* | 1.00 | 0.02 | 0.946 | −0.07 | 0.95–1.05 | 1.05 | 0.04 | 0.131 | 1.51 | 0.98–1.13 |
Bleeding any time in pregnancy (vs none) | 1.04 | 0.08 | 0.598 | 0.53 | 0.89–1.22 | 1.01 | 0.12 | 0.924 | 0.10 | 0.80–1.27 |
Any previous abortion up to 23rd week (vs none) |
1.17
|
0.08
|
0.025
|
2.25
|
1.02–1.34
| 1.00 | 0.09 | 0.955 | 0.06 | 0.85–1.19 |
University education grandparents (vs < university) | 1.09 | 0.08 | 0.211 | 1.25 | 0.95–1.25 |
0.82
|
0.07
|
0.022
|
−2.28
|
0.69–0.97
|
Mother is immigrant (vs native) | 0.89 | 0.07 | 0.111 | −1.59 | 0.76–1.03 | 0.94 | 0.11 | 0.587 | −0.54 | 0.74–1.18 |
Single/separated/divorced (vs cohabiting/married) | 0.98 | 0.10 | 0.873 | −0.16 | 0.81–1.20 |
0.76
|
0.10
|
0.042
|
−2.03
|
0.58–0.99
|
Travel time hospital at birth (per 30 min from avg.)* | 0.97 | 0.02 | 0.160 | −1.40 | 0.92–1.01 | 0.95 | 0.03 | 0.079 | −1.75 | 0.89–1.01 |
Western health authority (vs South-Eastern) | 0.92 | 0.06 | 0.227 | −1.21 | 0.80–1.05 | 1.15 | 0.11 | 0.153 | 1.43 | 0.95–1.38 |
Central health authority (vs South-Eastern) | 1.04 | 0.08 | 0.624 | 0.49 | 0.89–1.21 |
1.32
|
0.12
|
0.003
|
3.00
|
1.10–1.59
|
Northern health authority (vs South-Eastern) | 0.96 | 0.10 | 0.719 | −0.36 | 0.79–1.18 |
1.39
|
0.23
|
0.046
|
1.99
|
1.01–1.93
|
Reference rate per 1000 children per year |
1133
|
192
|
<0.001
|
41
|
812–1579
|
502
|
115
|
<0.001
|
27
|
320–786
|