Table 2.

Birth order and number of siblings in relationship to leukemia risk (unadjusted data)

Childhood ALLChildhood AMLAdult ALLAdult AML
CasesControlsOR (95% CI)CasesControlsOR (95% CI)CasesControlsOR (95% CI)CasesControlsOR (95% CI)
Birth order
 First8943,4281a (—)1687221a (—)5632,1501a (—)2,0788,0701a (—)
 Second7092,9880.91 (0.82–1.02)1666051.18 (0.93–1.50)2681,1890.85 (0.72–1.01)7793,2480.92 (0.84–1.01)
 Third3671,4650.96 (0.84–1.10)783211.05 (0.78–1.41)1295430.90 (0.73–1.12)3151,2580.96 (0.84–1.10)
 ≥Fourth2299150.96 (0.82–1.13)491961.07 (0.75–1.54)903181.07 (0.83–1.39)1908720.83b (0.70–0.99)
 For each increase by 10.99 (0.95–1.03)1.01 (0.93–1.09)1.02 (0.96–1.08)0.96b (0.92–1.00)
Birth order
 First8943,4281a (—)1687221a (—)5632,1501a (—)2,0788,0701a (—)
 Later1,3055,3680.93 (0.85–1.03)2931,1221.12 (0.91–1.39)4872,0500.90 (0.78–1.04)1,2845,3780.92b (0.84–1.00)
Number of younger siblings
 01,3355,3271a (—)3091,1811a (—)4891,9221a (—)1,7386,5221a (—)
 16812,7680.98 (0.88–1.09)1084690.86 (0.66–1.11)2751,2240.88 (0.75–1.04)8153,4250.89b (0.81–0.98)
 21475531.06 (0.87–1.30)321410.84 (0.55–1.27)1495831.00 (0.82–1.23)4541,8310.93 (0.83–1.05)
 ≥3361480.97 (0.67–1.42)12530.83 (0.43–1.58)1374711.15 (0.92–1.42)3551,6700.80c (0.70–0.90)
 For each increase by 11.00 (0.94–1.08)0.93 (0.80–1.07)1.02 (0.97–1.07)0.95c (0.93–0.98)
  • aReference category.

  • bP < 0.05.

  • cP < 0.001.