Skip to main content

Table 1 Characteristics of Michigan births and unadjusted odds ratios for a male birth from parents in the Michigan Long-Term PBB Study (n = 865 offspring born 1975–1988)

From: A cohort study of the association between secondary sex ratio and parental exposure to polybrominated biphenyl (PBB) and polychlorinated biphenyl (PCB)

Characteristic N%
Offspring
Unadjusted
OR^ (95% CI)
Maternal age at offspring's birth (years)   
   < 30 735 (85) 1.00
   ≥ 30 130 (15) 1.29 (0.89, 1.86)
Paternal age at offspring's birth (years)   
   < 35 740 (89) 1.00
   ≥ 35 89 (11) 0.95 (0.64, 1.39)
Maternal education at offspring's birth   
   ≤ HS 543 (63) 1.00
   > HS 320 (37) 1.09 (0.83, 1.42)
Paternal education at offspring's birth   
   ≤ HS 524 (63) 1.00
   > HS 304 (37) 1.06 (0.81, 1.38)
Maternal BMI at enrollment (kg/m2)*   
   < 18.5 60 (9) 0.93 (0.55, 1.58)
   18.5–24.9 466 (67) 1.00
   ≥ 25 171 (24) 0.96 (0.72, 1.29)
Paternal BMI at enrollment (kg/m2)*   
   < 18.5 4 (1) 0.77 (0.27, 2.23)
   18.5–24.9 173 (57) 1.00
   ≥ 25 129 (42) 1.43 (0.98, 2.09)
Months unprotected intercourse to achieve pregnancy **   
   1–3 months 300 (59) 1.00
   >3 months 210 (41) 0.94 (0.67, 1.31)
Birth order   
   First-born 325 (38) 1.00
   Non first-born 540 (62) 1.08 (0.81, 1.42)
Offspring gestation (weeks)   
   < 37 30 (4) 1.78 (0.86, 3.67)
   37 to <42 664 (77) 1.00
   ≥ 42 165 (19) 0.99 (0.71, 1.37)
  1. ^ ORs are unadjusted for covariates, but adjusted for offspring born to the same mother or father
  2. * Maternal enrollment BMI restricted to mothers' ages ≥ 16 years and fathers' ages ≥ 19 years
  3. ** Mothers who reported "doing something to prevent the pregnancy" were not asked the follow-up question of how many months of unprotected intercourse it took to achieve pregnancy (for n = 112 offspring)