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Table 2 Characteristics of study sample by influenza status

From: Risk of pregnancy complications and adverse birth outcomes after maternal A(H1N1)pdm09 influenza: a Norwegian population-based cohort study

  Without influenza, n = 1032 With influenza, n = 226
Influenza risk group (%) 5.6 13.3
Age of mother, years (mean) 32.0 31.6
No previous births, (%) 46.7 37.6
Use of folic acid during pregnancy (%) 69.6 71.2
Smoking during pregnancy (%) 4.5 1.3
Date of pregnancy start (median) Oct 02, 2009 Sept 12, 2009
Second or third trimester at start of pandemic (%)a 5.6 8.4
Days between end of pandemic and birth (mean)b 186 170
Date of birth (median) July 11, 2010 June 21, 2010
Recruited from the Norwegian Mother and Child Cohort Study (%) 15.1 14.2
Blood sample collected at birth (%) 61.3 68.6
  1. aStart of pandemic defined as October 1, 2009
  2. bEnd of pandemic defined as December 31, 2009