Table 2. Risk factors associated with increase in mean maternally-derived RSV IgG post-F antibody levels, England, 2008–2013 (n = 683 children)a .
| Risk factor | Distribution of children included in the analyses by each risk factor (n = 683)b | Adjusted ratios of geometric mean maternally-derived IgG post-F antibody levels (95% CI)c,d | |
|---|---|---|---|
| N | % | ||
| Gestational age (weeks) | |||
| < 35 | 29 | 4.2 | 0.65 (0.48–0.89) |
| 35–36 | 47 | 6.9 | 0.90 (0.70–1.16) |
| 37–40 (baseline) | 480 | 70.3 | 1 (baseline) |
| ≥ 41 | 127 | 18.6 | 1.19 (1.01–1.39) |
| Parity | |||
| 0 (baseline) | 227 | 33.2 | 1 (baseline) |
| 1 | 203 | 29.7 | 1.20 (1.03–1.40) |
| 2 | 124 | 18.2 | 1.18 (0.99–1.42) |
| ≥ 3 | 129 | 18.9 | 1.08 (0.90–1.30) |
| Time of birth | |||
| Jan–Mar | 186 | 27.2 | 1.19 (1.00–1.42) |
| Apr–Jun | 165 | 24.2 | 1.22 (1.02–1.46) |
| Jul–Sep | 159 | 23.3 | 1.22 (1.03–1.46) |
| Oct–Dec (baseline) | 173 | 25.3 | 1 (baseline) |
CI: confidence interval; IgG post-F: immunoglobulin G antibody against RSV postfusion protein F; RSV: respiratory syncytial virus.
a The cohort included 700 children with cord blood samples, of whom 683 had complete information on all risk factors included in the final analyses of maternally-derived antibody concentrations.
b The number and percentages of children, per risk factor category included in the final model, are presented.
c The exponentiated results from the loge-linear model (mutually adjusted for all variables in the table), reflecting proportional change in maternally-derived IgG post-F levels for each risk factor category relative to the baseline are shown.
d The mean maternally-derived RSV IgG post-F antibody concentration at baseline (gestational age of 37–40 weeks, parity of 0 and birth in October–December) was 268 arbitrary units/mL (95% CI: 229–314 arbitrary units/mL).