title: Perfluoroalkyl acids and time to pregnancy revisited: An update from the Danish National Birth Cohort.
abstract: BACKGROUND
  We previously demonstrated an association between plasma perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) and longer time to pregnancy (TTP) in a sample from the Danish National Birth Cohort (DNBC, 1996-2002). In this study we investigated this association in a new sample from the same cohort.
  
  
  METHODS
  Sample 1 consisted of 440 women, and Sample 2 consisted of 1161 women from whom we previously published the associations between PFOS or PFOA and TTP. We performed sample-specific and pooled analyses using discrete-time survival analyses to estimate fecundability ratios according to PFOS and PFOA quartiles, adjusted for potential confounders chosen guided by a directed acyclic graph. We also estimated odds ratios for infertility (TTP > 12 months or infertility treatment) according to PFOS and PFOA by multivariable logistic regression.
  
  
  RESULTS
  In Sample 1 PFOS was not associated with lower fecundability ratios or infertility, and there was a tendency towards longer TTP with increasing PFOA only in parous women. In Sample 2 previously reported associations were again seen. In the pooled analyses including both parous and nulliparous women fecundability ratios were 13-22 % lower for the three higher quartiles of PFOS or PFOA compared to the reference quartile.
  
  
  CONCLUSIONS
  The pooled analyses were driven by the larger old sample, but we did not corroborate our previous finding of an association between high PFOS and longer TTP in the new sample. The tendency towards an association for PFOA and TTP in parous women may be due to reverse causation. Results from the new sample are more in line with the recent literature.
authors.affiliation: Perinatal Epidemiology Research Unit, Aarhus University Hospital, Skejby, Denmark. ccbach@clin.au.dk.
authors.forename: Cathrine Carlsen
authors.initials: CC
authors.lastname: Bach
authors.affiliation: Department of Epidemiology, Fielding School of Public Health, University of California, Los Angeles, USA. zeyanliew@gmail.com.
authors.forename: Zeyan
authors.initials: Z
authors.lastname: Liew
authors.affiliation: Section for Epidemiology, Department of Public Health, Aarhus University, Aarhus, Denmark. bhb@ph.au.dk.
authors.forename: Bodil Hammer
authors.initials: BH
authors.lastname: Bech
authors.affiliation: Institute of Clinical Research, University of Southern Denmark, Odense, Denmark. eanohr@health.sdu.dk.
authors.forename: Ellen Aagaard
authors.initials: EA
authors.lastname: Nohr
authors.affiliation: Department of Global Surveillance & Pharmacoepidemiology, AbbVie Inc, North Chicago, USA. chunyuanfei@gmail.com.
authors.forename: Chunyuan
authors.initials: C
authors.lastname: Fei
authors.affiliation: Centre for Arctic Health & Unit for Cellular and Molecular Toxicology, Department of Public Health, Aarhus University, Aarhus, Denmark. ebj@ph.au.dk.
authors.forename: Eva Cecilie
authors.initials: EC
authors.lastname: Bonefeld-Jorgensen
authors.affiliation: Perinatal Epidemiology Research Unit, Aarhus University Hospital, Skejby, Denmark. tbh@dadlnet.dk.|Department of Paediatrics, Aarhus University Hospital, Skejby, Denmark. tbh@dadlnet.dk.
authors.forename: Tine Brink
authors.initials: TB
authors.lastname: Henriksen
authors.affiliation: Department of Epidemiology, Fielding School of Public Health, University of California, Los Angeles, USA. jo@ph.au.dk.|Section for Epidemiology, Department of Public Health, Aarhus University, Aarhus, Denmark. jo@ph.au.dk.
authors.forename: Jørn
authors.initials: J
authors.lastname: Olsen
mesh_terms: D000328:Adult; D017738:Alkanesulfonic Acids / Q000097:blood*; D002210:Caprylates / Q000097:blood*; D015331:Cohort Studies; D003718:Denmark; D004785:Environmental Pollutants / Q000097:blood*; D005260:Female; D005298:Fertility / Q000187:drug effects*; D005466:Fluorocarbons / Q000097:blood*; D006801:Humans; D016015:Logistic Models; D016017:Odds Ratio; D011247:Pregnancy; D061685:Time-to-Pregnancy / Q000187:drug effects*
chemical_list: D017738:Alkanesulfonic Acids; D002210:Caprylates; D004785:Environmental Pollutants; D005466:Fluorocarbons