Table 4.

Results of the combined exposure of weekly working hours and physical work load on iatrogenic PTB in employed women only (N=4865)

		N	Iatrogenic PTB	Adjusted*
			OR (95% CI)
			Crude
	Physical work load
Weekly working hours	Low (ref)	824	1.0	1.0
8–31	Moderate	784	1.27 (0.25–3.59)	1.16 (0.22–4.87)
	High	262	2.58 (0.90–7.35)	2.24 (0.87–6.50)
Weekly working hours	Low	1790	1.29 (0.46–3.60)	0.97 (0.34–2.76)
≥32	Moderate	919	2.01 (0.69–5.80)	1.25 (0.42–3.72)
	High	242	4.92 (1.55–13.96)	3.42 (1.04–8.21)

Goodness of fit tests showed no evidence of lack of fit (p>0.40 for the adjusted logistic model).

Bold values indicate statistically significance at the level of p<0.05.

*Model adjusted for: parity, smoking, previous PTB, ethnicity, maternal educational level, maternal age and maternal pre-pregnancy BMI.

BMI, body mass index; PTB, preterm birth.