title: Seasonal variation in pre-eclamptic rate and its association with the ambient temperature and humidity in early pregnancy.
abstract: OBJECTIVE
  To determine any relationship between ambient temperatures adjusted for humidity at conception and the occurrence of pre-eclampsia.
  
  
  METHODS
  The subjects were singleton primiparae delivered in a Teaching Hospital between 1995 and 2002. We studied the odds of developing pre-eclampsia across months and investigated the association between the pre-eclamptic rates based on the months of conception and the mean monthly heat index.
  
  
  RESULTS
  A total of 245 (1.6%) women were diagnosed pre-eclampsia and eclampsia during the study period. There was a significant association between the seasons of conception and rate of pre-eclampsia (logistic regression Wald chi(2) = 9.2, p = 0.03). Conceptions during summer had a higher risk of pre-eclampsia than those during autumn (2.3 vs. 1.6%, OR 1.7, 95% CI 1.2-2.5). Women who conceived in June had the highest risk of developing pre-eclampsia (OR 2.8, 95% CI 1.5-5.2) while women who conceived in October had the lowest after adjusting for age. A 2-month time lag was observed between the peak pre-eclamptic rate in women who conceived in June and the peak heat index in August.
  
  
  CONCLUSIONS
  Singleton primiparous women who conceived in summer and had a longer exposure to higher ambient temperature were at a greater risk of pre-eclampsia.
authors.affiliation: Department of Obstetrics and Gynecology, The Chinese University of Hong Kong, Hong Kong, SAR, China. tamwh@cuhk.edu.hk
authors.forename: Wing Hung
authors.initials: WH
authors.lastname: Tam
authors.forename: Daljit S
authors.initials: DS
authors.lastname: Sahota
authors.forename: Tze Kin
authors.initials: TK
authors.lastname: Lau
authors.forename: Chi Yin
authors.initials: CY
authors.lastname: Li
authors.forename: Tak Yuen
authors.initials: TY
authors.lastname: Fung
mesh_terms: D000328:Adult; D002681:China / Q000453:epidemiology; D005260:Female; D005306:Fertilization; D006801:Humans; D006813:Humidity; D015994:Incidence; D011225:Pre-Eclampsia / Q000453:epidemiology*; D011247:Pregnancy; D012307:Risk Factors; D012621:Seasons; D013696:Temperature; D013997:Time Factors