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Table 3 Relationship between paternal smoking and preterm birth

From: Paternal smoking and preterm birth: a population-based retrospective cohort study among non-smoking women aged 20–49 years in rural China

Smoking amounts No. (%) HR (95% CI)
Model Ib Model IIc
Paternal smoking  
 No 3,760,013 (7.46) 1 [Reference] 1 [Reference]
 Yes 1,538,030 (8.12) 1.09 (1.08–1.10) 1.07 (1.06–1.07)
 1–4 208,098 (8.26) 1.11 (1.09–1.12) 1.05 (1.03–1.06)
 5–9 360,518 (7.99) 1.07 (1.06–1.09) 1.04 (1.03–1.05)
 10–14 537,788 (8.00) 1.07 (1.06–1.09) 1.05 (1.04–1.07)
 15–19 101,598 (7.97) 1.07 (1.05–1.09) 1.07 (1.05–1.10)
 ≥ 20 317,154 (8.45) 1.14 (1.12–1.15) 1.13 (1.12–1.14)
 P linear 0.140 0.007
Preconception paternal smokinga
 No 3,760,013 (7.46) 1 [Reference] 1 [Reference]
 Yes 190,529 (8.12) 1.08 (1.06–1.10) 1.07 (1.06–1.09)
 1–4 25,601 (8.16) 1.09 (1.04–1.13) 1.04 (0.99–1.08)
 5–9 43,887 (8.02) 1.07 (1.04–1.11) 1.05 (1.01–1.08)
 10–14 66,285 (7.91) 1.05 (1.02–1.08) 1.06 (1.03–1.09)
 15–19 12,020 (8.34) 1.12 (1.05–1.19) 1.14 (1.07–1.21)
 ≥ 20 40,882 (8.37) 1.12 (1.08–1.16) 1.15 (1.11–1.19)
 P linear 0.054 0.003
  1. CI confidence interval, OR odds ratio
  2. aParticipants whose husband still smoked during early-pregnancy or did not provide such information were excluded
  3. bORs were adjusted by maternal age at last menstrual period
  4. cORs were adjusted by maternal and paternal age at last menstrual period, maternal higher education, Han ethnic, preconception body mass index and alcohol drinking