title: Climate change is associated with male:female ratios of fetal deaths and newborn infants in Japan.
abstract: OBJECTIVE
  To evaluate whether climate change is associated with male:female ratios (sex ratios) of fetal deaths and births in Japan.
  
  
  METHODS
  A population-based cohort study.
  
  
  METHODS
  Not applicable.
  
  
  METHODS
  Newborn infants and fetuses spontaneously aborted after 12 weeks of gestation.
  
  
  METHODS
  None.
  
  
  METHODS
  Yearly sex ratios of fetal deaths and newborn infants and monthly fetal death rates and sex ratios of newborn infants.
  
  
  RESULTS
  A statistically significant positive association was found between yearly temperature differences and sex ratios of fetal deaths; a statistically significant negative association was found between temperature differences and sex ratios of newborn infants from 1968 to 2012, and between sex ratios of births and of fetal deaths. The sex ratios of fetal deaths have been increasing steadily along with temperature differences, whereas the sex ratios of newborn infants have been decreasing since the 1970s. Two climate extremes, a very hot summer in 2010 and a very cold winter in January 2011, showed not only statistically significant declines in sex ratios of newborn infants 9 months later in June 2011 and October 2011 but also statistically significant increases of fetal death rates immediately, in September 2010 and January 2011.
  
  
  CONCLUSIONS
  The recent temperature fluctuations in Japan seem to be linked to a lower male:female sex ratio of newborn infants, partly via increased male fetal deaths. Male concepti seem to be especially vulnerable to external stress factors, including climate changes.
authors.affiliation: M&K Health Institute, Ako, Hyogo, Japan. Electronic address: web@fukuda8767.com.
authors.forename: Misao
authors.initials: M
authors.lastname: Fukuda
authors.affiliation: M&K Health Institute, Ako, Hyogo, Japan.
authors.forename: Kiyomi
authors.initials: K
authors.lastname: Fukuda
authors.affiliation: Shimizu Women's Clinic, Minamiguchi, Takarazuka, Hyogo, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Shimizu
authors.affiliation: Shimizu Women's Clinic, Minamiguchi, Takarazuka, Hyogo, Japan.
authors.forename: Miho
authors.initials: M
authors.lastname: Nobunaga
authors.affiliation: Laboratory of Reproductive Biology, Juliane Marie Center for Children, Women and Reproduction, Rigshospitalet, University Hospital of Copenhagen, Copenhagen, Denmark.
authors.forename: Linn Salto
authors.initials: LS
authors.lastname: Mamsen
authors.affiliation: Laboratory of Reproductive Biology, Juliane Marie Center for Children, Women and Reproduction, Rigshospitalet, University Hospital of Copenhagen, Copenhagen, Denmark.
authors.forename: Claus
authors.initials: C
authors.lastname: Yding Andersen
mesh_terms: D000022:Abortion, Spontaneous / Q000401:mortality*; D057231:Climate Change / Q000401:mortality* / Q000706:statistics & numerical data*; D015331:Cohort Studies; D005260:Female; D046689:Fetal Mortality; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D007564:Japan / Q000453:epidemiology; D008297:Male; D054238:Perinatal Mortality; D011247:Pregnancy; D012307:Risk Factors; D012744:Sex Ratio
keywords: Climate change; climate extreme; sex ratio of fetal deaths; sex ratio of newborn infants; temperature difference