Table 1 Characteristics of the mothers and pregnancies

Age at delivery

Years, mean (SD)

31.1 (± 5.6)

29.3 (± 5.3)

< 0.001*

< 20

20–24

25–29

30–34

35–40

40–44

≥ 45

107 (1.6%)

700 (10.6%)

1,800 (27.3%)

2,124 (32.2%)

1,345 (20.4%)

469 (7.5%)

25 (0.4%)

1,288 (2.5%)

8,548 (16.4%)

16,917 (32.5%)

16,732 (32.2%)

6,888 (13.3%)

1,556 (3.0%)

52 (0.1%)

Pre-pregnancy BMI

kg/m², mean (SD)

28.4 (± 6.1)

23.7 (± 4.3)

< 0.001*

< 18.5

18.5–24.9

25–30

30–34.9

≥ 35

Missing

84 (1.3%)

2,001 (30.3%)

2,086 (31.6%)

1,389 (21.1%)

889 (13.5%)

148 (2.2%)

2016 (3.9%)

33,781 (65.0%)

10,222 (19.7%)

3,105 (6.0%)

1,213 (2.3%)

1644 (3.2%)

Parity

Mean (SD)

1.25 (± 1.6)

1.02 (± 1.4)

< 0.001*

First

Second or more

2,394 (36.3%)

4,203 (63.7%)

22,363 (43.0%)

29,618 (57.0%)

Smoking

< 0.001**

Yes

No

Missing

1,177 (17.8%)

5,278 (80.0%)

142 (2.2%)

7,802 (15.0%)

42,816 (82.4%)

1,363 (2.6%)

Gestational age at delivery

Weeks, mean (SD)

39.6 (± 1.7)

39.9 (± 1.8)

< 0.001*

Preterm birth < 37 weeks

Term birth ≥ 37 weeks

Missing

333 (5.1%)

6,258 (94.9%)

6 (0.1%)

2,145 (4.1%)

51,095 (95.7%)

76 (0.1%)

Perinatal mortality

0.436**

Yes

No

25 (0.4%)

6572 (96.6%)

232 (0.4%)

51,749 (96.6%)