Table 2

Univariate logistic regression analyses of the effects of individual characteristics on time to pregnancy (>6 months), preterm birth (<37 weeks) and decreased birth weight (<3000 g) among women in a birth cohort study

Variables	Prolonged time to pregnancy (n=3719), OR (95% CI)	Preterm birth (n=6302), OR (95% CI)	Decreased birth weight (n=6201), OR (95% CI)
Individual characteristics
Age at enrolment in study
<25 years	1.00	1.00	1.00
25–30 years	0.94 (0.71 to 1.23)	1.02 (0.74 to 1.41)	0.72 (0.60 to 0.87)^*
30–35 years	1.06 (0.82 to 1.37)	0.88 (0.65 to 1.21)	0.61 (0.51 to 0.72)^*
≥35 years	1.72 (1.30 to 2.29)^*	0.89 (0.61 to 1.30)	0.65 (0.52 to 0.80)^*

Educational level
Low	1.00	1.00	1.00
Mid-low	0.83 (0.67 to 1.02)	0.81 (0.61 to 1.08)	0.80 (0.68 to 0.94)^*
Mid-high	0.56 (0.44 to 0.71)^*	0.63 (0.45 to 0.89)^*	0.58 (0.47 to 0.70)^*
High	0.57 (0.46 to 0.71)^*	0.71 (0.52 to 0.96)^*	0.51 (0.43 to 0.62)^*

Country of origin
Netherlands	1.00	1.00	1.00
Surinam and Dutch Antilles	1.26 (0.94 to 1.68)	1.50 (1.08 to 2.10)^*	2.85 (2.37 to 3.43)^*
Morocco and Turkey	1.00 (0.79 to 1.27)	1.04 (0.73 to 1.49)	1.05 (0.85 to 1.30)
Other	1.04 (0.85 to 1.26)	1.18 (0.89 to 1.57)	1.29 (1.10 to 1.53)^*

Parity
First child	1.00	1.00	1.00
Second child and higher	0.66 (0.57 to 0.78)^*	0.63 (0.50 to 0.80)^*	0.51 (0.45 to 0.59)^*

Smoker during mid-pregnancy	1.65 (1.32 to 2.06)^*	1.10 (0.80 to 1.50)	1.77 (1.49 to 2.09)^*
Alcohol use during mid-pregnancy	0.78 (0.65 to 0.90)^*	0.85 (0.67 to 1.08)	0.80 (0.70 to 0.92)^*

Occupational characteristics
Paid employment	0.94 (0.78 to 1.13)	0.76 (0.60 to 0.95)^*	0.78 (0.68 to 0.89)^*
Job skill level
Elementary education	1.00	1.00	1.00
Lower secondary education	0.74 (0.42 to 1.31)	2.36 (0.85 to 6.58)	0.85 (0.57 to 1.28)
Higher secondary education	0.69 (0.40 to 1.21)	1.74 (0.63 to 4.84)	0.59 (0.39 to 0.89)^*
Tertiary education	0.52 (0.29 to 0.90)^*	1.37 (0.49 to 3.86)	0.49 (0.32 to 0.73)^*
Academic education	0.57 (0.32 to 1.03)	1.65 (0.57 to 4.74)	0.48 (0.31 to 0.74)^*

↵* p<0.05.