Table 3.

Combined score and associated risk for prematurity

Risk Scorea	Total Number	Controls (N = 343)	Cases (N = 342)	OR (95% CI)	P-value
0	259	172	87	–	–
1	330	150	180	2.37 (1.69–3.32)	< 0.001
2	82	20	62	6.13 (3.48–10.80)	< 0.001
3	14	1	13	25.70 (3.31–199.70)	0.002

^aThe cumulative individual risk score for each mother was calculated as the sum of values (0 for negative or 1 for positive) for each significant risk factor (long working hours, stress and maternal age). Maternal age was classified as 1 for values ≥30 years old and as 0 for values < 30 years old (30 years was the median value for mother age at childbirth in our dataset)