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Table 1 The proportion of preterm deliveries in Sweden, 1995–2004, presented according to gestational age groups, selected risk factors and the rate and absolute number of the reference population.

From: Reference population for international comparisons and time trend surveillance of preterm delivery proportions in three countries

Sweden

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

p-value for trend4

Deliveries (n)

100319

93104

87451

84243

84473

87710

88634

92041

95740

98512

 

22–27 w

0.22

0.24

0.22

0.28

0.29

0.21

0.26

0.27

0.29

0.26

0.012 (I)5

28–31 w

0.56

0.63

0.57

0.58

0.61

0.58

0.60

0.62

0.58

0.57

0.63

32–36 w

4.9

4.8

4.8

4.8

4.9

4.9

4.8

4.8

4.8

5.0

0.91

< 37 w

5.6

5.7

5.6

5.7

5.8

5.7

5.6

5.7

5.7

5.8

0.41

Women not born in Sweden

17.5

17.7

18.0

18.3

18.2

18.2

18.5

18.8

19.0

19.8

< 0.001 (I)

IVF or ICSI

0.6

1.4

1.8

1.6

1.8

1.6

1.8

2.0

2.2

2.2

< 0.001 (I)

Multiples

1.5

1.5

1.6

1.6

1.6

1.5

1.6

1.5

1.7

1.4

0.48

Primiparous 1

40.2

41.3

41.4

41.5

42.3

44.0

44.7

45.5

45.2

45.0

< 0.001 (I)

Iatrogenic delivery 2

14.1

14.0

14.9

15.9

17.0

16.9

18.1

18.5

19.0

19.5

< 0.001 (I)

Age < 20

2.1

2.0

2.0

1.9

2.0

2.0

1.9

1.9

1.7

1.6

< 0.001(R)6

Age ≥35

13.3

13.8

14.1

15.4

16.0

16.8

17.9

18.3

19.3

19.9

< 0.001 (I)

Reference population 3 (% of all births)

29.6

29.9

30.0

29.6

29.9

31.2

31.3

31.7

31.1

30.3

< 0.001 (I)

Reference population 3 (n)

29685

27875

26249

24926

25232

27354

27762

29133

29775

29825

 
  1. P-values for trend are presented.
  2. 1 Primiparous: the index pregnancy resulted in delivery for the first time.
  3. 2 Induced delivery or caesarean section.
  4. 3 Reference population: 20 – 35-years-old primiparas, born in Sweden, with singleton, spontaneously conceived pregnancies.
  5. 4 p-values obtained from simple logistic regression analyses with the dichotomized variables specified as outcome variables, and year of birth as the only independent variable.
  6. 5(I) = Increase
  7. 6(R) = Reduction