A cohort study of the association between secondary sex ratio and parental exposure to polybrominated biphenyl (PBB) and polychlorinated biphenyl (PCB).
BACKGROUND
Polybrominated biphenyl (PBB), a brominated flame retardant, was accidently mixed into animal feed in Michigan (1973-1974) resulting in human exposure through consumption of contaminated meat, milk and eggs. Beginning in 1976 individuals who consumed contaminated products were enrolled in the Michigan Long-Term PBB Study. This cohort presents a unique opportunity to study the association between parental exposures to PBB and offspring sex ratio.


METHODS
We identified offspring of female PBB cohort participants (born 1975-1988) and obtained electronic birth records for those born in the state of Michigan. We linked this information to parental serum PBB and PCB concentrations collected at enrollment into the cohort. We modeled the odds of a male birth with generalized estimating equations accounting for the non-independence of siblings born to the same parents. We explored potential confounders: parental age and education at offspring's birth, parental body mass index at cohort enrollment, birth order, gestational age and year of offspring's birth.


RESULTS
The overall proportion of male offspring among 865 live births to cohort mothers was 0.542. This was higher than the national male proportion of 0.514 (binomial test: p = 0.10). When both parents were in the cohort (n = 300), we found increased odds of a male birth with combined parents' enrollment PBB exposure > or = the median concentrations (3 microg/L for mothers; 6 microg/L for fathers) compared to combined parents' PBB exposure < the median concentrations (AOR = 1.43, 95% CI: 0.89-2.29), although this did not reach statistical significance. In addition, there was a suggestion of increased odds of a male birth for combined parents' enrollment PCB exposure > or = the median concentrations (6 microg/L for mothers; 8 microg/L for fathers) compared to combined parents' enrollment PCB exposure < the median concentrations (AOR = 1.53, 95% CI: 0.93-2.52).


CONCLUSIONS
This study adds to the body of literature on secondary sex ratio and exposure to environmental contaminants. In this population, combined parental exposure to PBBs or PCBs increased the odds of a male birth. Further research is needed to corroborate these findings and shed light on the biological mechanisms by which these types of chemicals may influence the secondary sex ratio.
Terrell
Metrecia L
ML
Department of Epidemiology, Rollins School of Public Health, Emory University, 1518 Clifton Rd, Atlanta, Georgia 30322, USA. mterrel@emory.edu
Berzen
Alissa K
AK
Small
Chanley M
CM
Cameron
Lorraine L
LL
Wirth
Julie J
JJ
Marcus
Michele
M
D015331:Cohort Studies; D003710:Demography; D004785:Environmental Pollutants / Q000097:blood*; D005260:Female; D005506:Food Contamination; D005865:Gestational Age; D006801:Humans; D008297:Male; D018811:Maternal Exposure / Q000009:adverse effects* / Q000706:statistics & numerical data; D008824:Michigan / Q000453:epidemiology; D016017:Odds Ratio; D018812:Paternal Exposure; D011075:Polybrominated Biphenyls / Q000097:blood* / Q000633:toxicity; D011078:Polychlorinated Biphenyls / Q000097:blood* / Q000633:toxicity; D011247:Pregnancy; D011256:Pregnancy Outcome; D011297:Prenatal Exposure Delayed Effects; D017678:Sex Distribution; D012744:Sex Ratio
D004785:Environmental Pollutants; D011075:Polybrominated Biphenyls; D011078:Polychlorinated Biphenyls
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