Table 2 The proportion of preterm deliveries in Denmark, 1995–2004, presented according to gestational age groups, selected risk factors and the rate and absolute number of the reference population.

Deliveries (n)

68081

65891

66041

64816

64769

65699

64014

62648

63203

63226

22–27 w

0.22

0.26

0.22

0.20

0.23

0.21

0.26

0.23

0.29

0.25

< 0.001(I)⁵

28–31 w

0.60

0.68

0.63

0.65

0.64

0.65

0.63

0.65

0.67

0.67

0.11

32–36 w

4.5

4.9

4.5

4.7

4.6

4.8

5.2

5.2

5.2

5.2

< 0.001(I)

< 37 w

5.3

5.9

5.3

5.5

5.5

5.7

6.0

6.1

6.2

6.1

< 0.001(I)

Women not born in Denmark

17.0

18.3

19.2

19.6

20.4

20.8

20.9

21.2

20.8

20.2

< 0.001(I)

IVF or ICSI

1.2

1.5

1.9

2.0

2.4

2.8

3.0

3.0

3.4

2.5

< 0.001 (I)

Multiples

1.7

1.9

1.9

2.0

2.0

2.0

2.2

2.2

2.2

2.3

< 0.001(I)

Primiparous ¹

44.9

45.7

43.0

43.0

43.3

43.8

43.9

43.5

43.7

43.9

< 0.001(R)⁶

Iatrogenic delivery ²

15.0

15.3

10.0

11.5

13.7

15.6

17.3

19.4

19.8

20.7

< 0.001(I)

Age < 20

2.0

1.9

1.9

1.8

1.7

1.6

1.6

1.4

1.3

1.3

< 0.001(R)

Age ≥35

11.4

11.9

12.7

13.3

14.2

14.7

15.7

16.9

17.3

17.3

< 0.001(I)

Reference population ³ (% of all births)

33.3

33.4

30.3

30.4

30.1

30.2

30.2

29.6

29.8

30.6

< 0.001(R)

Reference population ³ (n)

22699

21977

20000

19732

19460

19843

19338

18522

18856

19322