Table 2 Hierarchical linear regression predicting birthweight (grams) of term newborns for the period 1999–2008 and 2008–2018

Model 0

 Intercept

3300

0.98

3298–3302

< 0.0001

3291

1.06

3289–3293

< 0.0001

 Calendar year (year)

4.14

0.17

3.80–4.47

< 0.0001

-2.48

0.15

-2.77-(-2.19)

< 0.0001

 Boy

136.1

0.99

134.1–138.0

< 0.0001

140.4

0.94

138.6-142.3

< 0.0001

Model 1

 Intercept

3297

1.00

3295–3299

< 0.0001

3288

1.06

3286–3290

< 0.0001

 Calendar year (year)

5.41

0.16

5.10–5.73

< 0.0001

-1.42

0.14

-1.68-(-1.15)

< 0.0001

 Boy

141.5

0.92

139.7-143.3

< 0.0001

144.8

0.87

143.1-146.5

< 0.0001

 Week of delivery (week)

145.0

0.89

143.3-146.8

< 0.0001

144.8

0.85

143.2-146.5

< 0.0001

 (week of delivery)²

-19.85

0.34

-20.51-(-19.18)

< 0.0001

-18.46

0.33

-19.10-(-17.82)

< 0.0001

 (week of delivery)³

1.78

0.28

1.22–2.33

< 0.0001

2.50

0.27

1.97–3.04

< 0.0001

Model 2

 Intercept

3319

1.04

3317–3321

< 0.0001

3304

1.08

3301–3306

< 0.0001

 Calendar year (year)

2.36

0.16

2.05–2.68

< 0.0001

-1.81

0.14

-2.08-(-1.55)

< 0.0001

 Boy

141.2

0.91

139.4–143.0

< 0.0001

144.9

0.86

143.2-146.6

< 0.0001

 Week of delivery (week)

143.3

0.42

141.6-145.1

< 0.0001

145.3

0.83

143.7–147.0

< 0.0001

 (week of delivery)²

-18.91

0.33

-19.57-(-18.25)

< 0.0001

-17.14

0.32

-17.77-(-16.51)

< 0.0001

 (week of delivery)³

1.80

0.28

1.25–2.34

< 0.0001

1.95

0.27

1.42–2.48

< 0.0001

 Maternal age (year)

9.41

0.09

9.30–9.65

< 0.0001

11.64

0.07

11.50-11.79

< 0.0001

 (maternal age)²

-0.91

0.01

-0.94-(-0.89)

< 0.0001

-0.71

0.01

-0.73-(-0.69)

< 0.0001

Model 3

 Intercept

3296

1.21

3294–3298

< 0.0001

3274

1.22

3271–3276

< 0.0001

 Calendar year (year)

2.62

0.16

2.30–2.93

< 0.0001

-1.82

0.14

-2.09-(-1.56)

< 0.0001

 Boy

141.0

0.91

139.3-142.8

< 0.0001

144.8

0.86

143.1-146.5

< 0.0001

 Week of delivery (week)

144.2

0.88

142.5–146.0

< 0.0001

148.0

0.84

146.4-149.6

< 0.0001

 (week of delivery)²

-18.62

0.34

-19.28-(-17.97)

< 0.0001

-16.49

0.32

-16.13-(-15.86)

< 0.0001

 (week of delivery)³

1.81

0.28

1.26–2.36

< 0.0001

1.68

0.27

1.15–2.21

< 0.0001

 Maternal age (year)

8.30

0.09

8.12–8.48

< 0.0001

10.43

0.08

10.28–10.59

< 0.0001

 (maternal age)²

-0.90

0.01

-0.92-(-0.88)

< 0.0001

-0.71

0.01

-0.73-(-0.69)

< 0.0001

 Multiparous

35.97

0.96

34.09–37.85

< 0.0001

47.81

0.90

46.04–49.57

< 0.0001

 Induced delivery

0.25

1.49

-2.67-3.17

NS

10.52

1.27

8.04–10.01

< 0.0001

 Caesarean section.

13.99

1.25

11.54–16.43

< 0.0001

11.57

1.08

9.45–13.69

< 0.0001