Table 2 Characteristics of study sample by influenza status
|  | 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 |