title: A cohort study of the association between secondary sex ratio and parental exposure to polybrominated biphenyl (PBB) and polychlorinated biphenyl (PCB).
abstract: 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.
authors.affiliation: Department of Epidemiology, Rollins School of Public Health, Emory University, 1518 Clifton Rd, Atlanta, Georgia 30322, USA. mterrel@emory.edu
authors.forename: Metrecia L
authors.initials: ML
authors.lastname: Terrell
authors.forename: Alissa K
authors.initials: AK
authors.lastname: Berzen
authors.forename: Chanley M
authors.initials: CM
authors.lastname: Small
authors.forename: Lorraine L
authors.initials: LL
authors.lastname: Cameron
authors.forename: Julie J
authors.initials: JJ
authors.lastname: Wirth
authors.forename: Michele
authors.initials: M
authors.lastname: Marcus
mesh_terms: 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
chemical_list: D004785:Environmental Pollutants; D011075:Polybrominated Biphenyls; D011078:Polychlorinated Biphenyls
references.citation: Fertil Steril. 1998 Aug;70(2):270-3
references.pmid: 9696219
references.citation: Environ Health Perspect. 2001 Nov;109(11):1127-32
references.pmid: 11712997
references.citation: Toxicology. 2001 Feb 14;158(3):141-53
references.pmid: 11275356
references.citation: J Expo Sci Environ Epidemiol. 2008 Jul;18(4):410-20
references.pmid: 18183045
references.citation: Arch Environ Health. 1982 May-Jun;37(3):141-7
references.pmid: 6284069
references.citation: Lancet. 1996 Sep 21;348(9030):828-9
references.pmid: 8814010
references.citation: Hum Reprod. 2004 Feb;19(2):442-4
references.pmid: 14747194
references.citation: Ann Epidemiol. 2007 Jul;17(7):503-10
references.pmid: 17448678
references.citation: Environ Res. 2007 Jan;103(1):99-105
references.pmid: 16780830
references.citation: Environ Res. 2006 Jan;100(1):77-85
references.pmid: 15922323
references.citation: Environ Health Perspect. 1995 Mar;103(3):272-4
references.pmid: 7768229
references.citation: Crit Rev Toxicol. 1985;16(2):105-56
references.pmid: 3002722
references.citation: Environ Health Perspect. 2000 Feb;108(2):147-52
references.pmid: 10656855
references.citation: Hum Reprod. 2005 Jul;20(7):1903-9
references.pmid: 15860497
references.citation: Environ Res. 2007 Oct;105(2):247-55
references.pmid: 17239850
references.citation: Environ Health. 2003 Mar 12;2(1):2
references.pmid: 12694628
references.citation: Environ Health Perspect. 2002 Nov;110(11):A699-701
references.pmid: 12417498
references.citation: Arch Environ Health. 1983 Jan-Feb;38(1):47-53
references.pmid: 6299210
references.citation: Lancet. 2002 Jul 13;360(9327):143-4
references.pmid: 12126828
references.citation: Am J Public Health. 1984 Apr;74(4):378-9
references.pmid: 6322600
references.citation: Lancet. 2000 May 27;355(9218):1858-63
references.pmid: 10866441
references.citation: Ann N Y Acad Sci. 1979 May 31;320:284-94
references.pmid: 222186
references.citation: Environ Health Perspect. 2005 Oct;113(10):1295-8
references.pmid: 16203237
references.citation: Environ Res. 1977 Feb;13(1):74-93
references.pmid: 191251
references.citation: Epidemiology. 1998 Jul;9(4):474-5
references.pmid: 9647916
references.citation: J Anal Toxicol. 1980 Jan-Feb;4(1):22-6
references.pmid: 6098783
references.citation: Environ Health Perspect. 1985 May;60:193-9
references.pmid: 3928345
references.citation: Environ Health. 2005 Aug 09;4:15
references.pmid: 16091135
references.citation: Occup Environ Med. 2001 Aug;58(8):540-1
references.pmid: 11452050
references.citation: Chemosphere. 2007 Oct;69(8):1295-304
references.pmid: 17617441
references.citation: Environ Res. 2007 Nov;105(3):370-9
references.pmid: 17485077
references.citation: J Occup Environ Med. 2002 Jan;44(1):8-13
references.pmid: 11802470
references.citation: Environ Health Perspect. 1985 May;60:399-403
references.pmid: 2992925
references.citation: J Assoc Off Anal Chem. 1981 Sep;64(5):1131-7
references.pmid: 6270054
references.citation: Natl Vital Stat Rep. 2005 Jun 14;53(20):1-17
references.pmid: 15974501
references.citation: Basic Clin Pharmacol Toxicol. 2008 Feb;102(2):176-81
references.pmid: 18226072
references.citation: Epidemiology. 2000 Nov;11(6):641-7
references.pmid: 11055623
references.citation: J Theor Biol. 1996 Jun 21;180(4):271-86
references.pmid: 8776463
references.citation: Environ Health Perspect. 2006 May;114(5):718-24
references.pmid: 16675426
references.citation: Sci Total Environ. 1996 Sep 9;187(3):199-210
references.pmid: 8711465
references.citation: Aquat Toxicol. 2005 Sep 10;74(3):272-9
references.pmid: 16024102
references.citation: CMAJ. 1997 Jan 1;156(1):37-41
references.pmid: 9006562
references.citation: Environ Health. 2008 Jul 15;7:37
references.pmid: 18627595