Table 2.
Associations of mean gestational age at birth and mean birth weight with pregnancy, parental and environmental factors from adjusted linear mixed-effects model (model 3)
| Gestational age (days) absolute differences (95% CI) |
Birth weight (g) * relative differences (95% CI) |
|||
| Eligible population | Complete case population | Eligible population | Complete case population | |
| Intercept | 277.3 (277.2 to 277.5) | 277.9 (277.7 to 278.2) | 3278 (3218 to 3339)† | 3298 (3180 to 3420)† |
| Sex | ||||
| Female | 0 | 0 | 1 | 1 |
| Male | −0.56 (-0.65 to -0.48) | −0.63 (-0.79 to -0.47) | 1.045 (1.044 to 1.046) | 1.048 (1.046, 1.049) |
| Birth rank | ||||
| 1‡ | 0 | 0 | 1 | 1 |
| 2 | −0.39 (-0.49 to -0.29) | −0.34 (-0.52 to -0.16) | 1.038 (1.037 to 1.039) | 1.039 (1.037, 1.041) |
| 3 | −0.37 (-0.52 to -0.22) | −0.16 (-0.44 to 0.11) | 1.050 (1.048 to 1.051) | 1.054 (1.051, 1.057) |
| ≥4 | −0.24 (-0.50 to 0.02) | 0.24 (-0.25 to 0.72) | 1.058 (1.056 to 1.061) | 1.065 (1.059, 1.070) |
| Age mother (years)§ | ||||
| <20 (per 5 years decr.) | −4.10 (-5.59 to -2.61) | – | 1.002 (0.987 to 1.017) | – |
| ≥20–30‡ | 0 | 0 | 1 | 1 |
| ≥30–40 (per 5 years) | −0.99 (-1.06 to -0.91) | −0.93 (-1.07 to -0.78) | 1.000 (1.000 to 1.001) | 0.998 (0.997, 1.000) |
| ≥40 (per 5 years) | −2.93 (-3.36 to -2.50) | −3.46 (-4.29 to -2.63) | 0.998 (0.994 to 1.003) | 0.998 (0.990, 1.006) |
| Civil status¶ | ||||
| Married | 0 | 0 | 1 | 1 |
| Not married | −0.01 (-0.13 to 0.10) | 0.15 (-0.08 to 0.38) | 0.990 (0.989 to 0.991) | 0.993 (0.99, 0.995) |
| Nationality mother | ||||
| Switzerland‡ | 0 | 0 | 1 | 1 |
| S Europe | 0.20 (-0.01 to 0.40) | 0.39 (00 to 0.78) | 0.994 (0.992 to 0.996) | 0.995 (0.991, 0.999) |
| W Europe | 0.20 (0.02 to 0.38) | −0.08 (-0.43 to 0.26) | 1.008 (1.006 to 1.010) | 1.007 (1.004, 1.011) |
| N Europe | 0.37 (-0.07 to 0.81) | 0.30 (-0.57 to 1.17) | 1.025 (1.020 to 1.029) | 1.022 (1.013, 1.031) |
| E Europe | 0.21 (0.04 to 0.38) | 0.33 (-0.01 to 0.68) | 1.013 (1.011 to 1.014) | 1.017 (1.014, 1.021) |
| Other | −0.32 (-0.49 to -0.14) | −0.67 (-1.05 to -0.30) | 1.007 (1.005 to 1.008) | 1.012 (1.008, 1.016) |
| Nationality father | ||||
| Switzerland‡ | 0 | 0 | 1 | 1 |
| S Europe | −0.46 (-0.64 to -0.28) | −0.28 (-0.62 to 0.06) | 0.991 (0.990 to 0.993) | 0.993 (0.989, 0.996) |
| W Europe | 0.07 (-0.11 to 0.25) | 0.30 (-0.04 to 0.63) | 1.008 (1.006 to 1.009) | 1.006 (1.003, 1.010) |
| N Europe | 0.51 (0.08 to 0.94) | −0.24 (-1.09 to 0.62) | 1.013 (1.009 to 1.017) | 1.011 (1.003, 1.020) |
| E Europe | −0.46 (-0.64 to -0.28) | −0.01 (-0.38 to 0.36) | 1.009 (1.007 to 1.010) | 1.011 (1.008, 1.015) |
| Other | −0.02 (-0.22 to 0.18) | 0.48 (0.05 to 0.90) | 0.992 (0.991 to 0.994) | 0.992 (0.987, 0.996) |
| Missing | −3.87 (-4.24 to -3.50) | – | 0.989 (0.985 to 0.992) | – |
| Education mother | ||||
| Tertiary‡ | 0 | 1 | ||
| Secondary | −0.55 (-0.74 to -0.36) | 0.996 (0.995, 0.998) | ||
| Compulsory | −0.90 (-1.22 to -0.58) | 0.993 (0.990, 0.996) | ||
| Education father | ||||
| Tertiary‡ | 0 | 1 | ||
| Secondary | −0.16 (-0.35 to 0.03) | 0.996 (0.994, 0.998) | ||
| Compulsory | −0.25 (-0.58 to 0.07) | 0.997 (0.994, 1.000) | ||
| Altitude (m) | ||||
| 500‡ | 0 | 0 | 1 | 1 |
| per 500 m increase | 0.07 (-0.09 to 0.23) | 0.03 (-0.24 to 0.30) | 0.989 (0.988 to 0.991) | 0.989 (0.987, 0.992) |
| Urbanisation | ||||
| Urban‡ | 0 | 0 | 1 | 1 |
| Peri-urban | −0.43 (-0.57 to -0.28) | −0.59 (-0.82 to -0.36) | 1.001 (1.000 to 1.002) | 1.003 (1.000, 1.005) |
| Rural | −0.15 (-0.32 to 0.02) | −0.29 (-0.55 to -0.02) | 1.000 (0.998 to 1.001) | 1.003 (1.001, 1.006) |
| Language region | ||||
| German‡ | 0 | 0 | 1 | 1 |
| French | −0.62 (-0.77 to -0.47) | −0.66 (-0.88 to -0.44) | 0.989 (0.987 to 0.990) | 0.988 (0.985, 0.990) |
| Italian | −0.94 (-1.26 to -0.63) | −1.11 (-1.55 to -0.68) | 0.982 (0.980 to 0.985) | 0.983 (0.979, 0.987) |
| Percent of spatial variance explained** | 31% | 39% | 87% | 88% |
*Birth weight was modelled on a log scale, which results in multiplicative effects. The model for birth weight was additionally adjusted for gestational age by a cubic spline function with knots at weeks 25, 30 and 35.
†In the model for BW, the intercept corresponds to an estimated mean birth weight (g) for a singleton girl born at gestational age 40 weeks as the first child (rank 1) in a German-speaking, urban region of elevation 500m, whose mother is 20-30 years old at birth and married, and both parents have Swiss nationality and tertiary education.
‡Reference category.
§Age modelled by a piece-wise linear function: constant at reference range ≥20-30, and separate slopes for age <20, ≥30-40, and ≥40.
¶Married or in registered partnership / Not married: Single, widow, divorced or in dissolved partnership.
**Percentage of regional variance explained by model predictors, i.e. percent reduction in variance of random effects (σ2) when compared to model with no predictors (model 0).