Table 2.
Demographic and maternal characteristics of study population
| Age at index date (N = 11,086 pregnancies)a | Mean ± SD |
| Maternal age, years | 29.5 ± 5.8 |
| Gestational age, weeks | 20.3 ± 11.6 |
| Ethnic category (N = 10,145 women) | Number (%) |
| Hispanic | 1113 (11.0) |
| Not Hispanic | 3559 (35.1) |
| Unknown | 5473 (53.9) |
| Racial categories (N = 10,145 women) | Number (%) |
| White | 7406 (73.0) |
| Asian/Pacific Islander | 917 (9.1) |
| Black or African American | 387 (3.8) |
| American Indian, Aleutian, or Eskimo | 75 (0.7) |
| Unknown | 1360 (13.4) |
| Gravidity (N = 11,086 pregnancies)a | Number (%) |
| 1 | 3208 (28.9) |
| 2 | 3021 (27.2) |
| 3 | 1965 (17.7) |
| 4 | 1071 (9.7) |
| ≥ 5 | 1069 (9.6) |
| Unknown | 752 (6.8) |
| Influenza risk status (N = 11,086 pregnancies)a | Number (%) |
| High risk | 1563 (14.1) |
| Normal risk | 9523 (85.9) |
a
Maternal age, gravidity, and influenza risk status were assessed for each pregnancy episode. Individual women were counted more than once if pregnant in multiple seasons.
SD = standard deviation.