Table 1.
Demographic characteristics of the Norwegian population born at term (39–41 weeks) in 1967–2015 according to their birth weighta
| Birth weight (in grams) | |||||||
|---|---|---|---|---|---|---|---|
| <2000 | 2000-<3000 | 3000-<3500 | 3500-<4000 | 4000-<5000 | ≥5000 | Any birth weight | |
|
|
|||||||
| N=1,010 (0.1%) | N=146,096 (8.0%) | N=582,523 (31.8%) | N=723,729 (39.5%) | N=372,734 (20.3%) | N=7,410 (0.4%) | N=1,833,502 (100%) | |
| Female | 57% | 61% | 55% | 47% | 39% | 29% | 49% |
| Weeks of gestation, mean | 39.7 | 39.7 | 39.9 | 40.0 | 40.2 | 40.4 | 40.0 |
| Birth year, mean | 1982 | 1989 | 1991 | 1992 | 1992 | 1993 | 1991 |
| Maternal age, years, mean | 26.7 | 26.9 | 27.4 | 28.0 | 28.7 | 29.8 | 27.9 |
| Maternal age ≥38 years | 6% | 4% | 4% | 4% | 5% | 8% | 4% |
| Nulliparous mothersb | 54% | 54% | 47% | 39% | 29% | 19% | 40% |
| Single mothers | 18% | 13% | 10% | 8% | 6% | 5% | 9% |
| Maternal educationc, mean | 3.5 | 3.9 | 4.1 | 4.3 | 4.4 | 4.3 | 4.2 |
| Paternal educationc, mean | 3.7 | 3.9 | 4.1 | 4.3 | 4.3 | 4.2 | 4.2 |
| Immigrant parents | 4% | 8% | 7% | 5% | 4% | 4% | 5% |
Abbreviations: N, number; SD, standard deviation;
a
Excluded are babies without registered birth weight, as well as stillbirths and multiple births.
b
Mothers that were nulliparous prior to birth of interest compared to parous.
c
Level of highest education on a national level scale of 0 (no formal education) to 8 (highest university degree, corresponding to a doctoral degree). Level 3 corresponds to 11–12 years and level 4 to 13 years of schooling.