title: Use of specified critical periods of different congenital abnormalities instead of the first trimester concept.
abstract: BACKGROUND
  Previously the first trimester, later the 2nd and/or 3rd gestational months were evaluated at the analysis of different exposures in different congenital abnormalities. However, different congenital abnormalities have different critical periods. The objective of this study was to check the feasibility of a new approach to consider the specified critical periods of different congenital abnormalities separately.
  
  
  METHODS
  The potential teratogenic effect of oral ampicillin treatment and maternal influenza/fever during the study pregnancy regarding any time in pregnancy, during the first trimester, in the 2nd and/or 3rd gestational months, and finally in the specified critical periods of given congenital abnormalities were evaluated in the population-based large data set of the Hungarian Case-Control Surveillance System of Congenital Abnormalities.
  
  
  RESULTS
  Of 22,843 cases, 1644 (7.2%) and 1328 (5.8%) were born to mothers who had oral ampicillin treatment or were affected with influenza/fever during the study pregnancy, while of 38,151 control newborns without any defect, 2631 (6.9 %) and 1838 (4.8%) had mothers with ampicillin treatment or influenza/fever, respectively. The analysis of different exposure time windows showed some difference in the risk for congenital abnormalities. The use of specified critical periods of different congenital abnormalities was feasible.
  
  
  CONCLUSIONS
  The use of specified critical periods of different congenital abnormalities seems to be more scientific-based than the previously accepted methods for the evaluation of different exposure time windows. Thus this new and feasible approach is recommended for the controlled epidemiological studies in the future after an international consensus in the specified critical periods of different congenital abnormalities and other methodological issues.
authors.affiliation: Foundation for the Community Control of Hereditary Diseases, Budapest, Hungary. czeizel@interware.hu
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Czeizel
authors.forename: Erzsébet H
authors.initials: EH
authors.lastname: Puhó
authors.forename: Nándor
authors.initials: N
authors.lastname: Acs
authors.forename: Ferenc
authors.initials: F
authors.lastname: Bánhidy
mesh_terms: D000013:Congenital Abnormalities; D005260:Female; D006801:Humans; D011247:Pregnancy; D011261:Pregnancy Trimester, First