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.
Denmark
 1995
 1996
 1997
 1998
 1999
 2000
 2001
 2002
 2003
 2004
 p-value for trend4
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)
Primiparous1
 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 delivery2
 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 population3 (% 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 population3 (n)
 22699
 21977
 20000
 19732
 19460
 19843
 19338
 18522
 18856
 19322

P-values for trend are presented.

1 Primiparous: the index pregnancy resulted in delivery for the first time.

2 Induced delivery or caesarean section.

3 Reference population: 20 – 35-years-old primiparas, born in Denmark, with singleton, spontaneously conceived pregnancies.

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.

5(I) = Increase

6(R) = Reduction

Morken et al. BMC Women's Health 2008 8:16   doi:10.1186/1472-6874-8-16