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

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)

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)

^ ORs are unadjusted for covariates, but adjusted for offspring born to the same mother or father
* Maternal enrollment BMI restricted to mothers' ages ≥ 16 years and fathers' ages ≥ 19 years
** 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)

ISSN: 1476-069X