Table 2.
Effect of letter type on survey completion by maternal characteristics
| Maternal characteristic | Odds ratio | 95 % confidence interval | p-value |
|---|---|---|---|
| Maternal age (years) | |||
| ≤24 | 2.20 | 1.22–3.96 | |
| 25–29 | 1.30 | 0.91–1.86 | 0.04 |
| 30–34 | 0.99 | 0.74–1.31 | |
| ≥35 | 0.88 | 0.62–1.24 | |
| Country of birth | |||
| Australia | 1.06 | 0.84–1.33 | 0.54 |
| Other | 1.19 | 0.90–1.57 | |
| Socio-economic index | |||
| 1 (lowest) | 1.1 | 0.5–2.5 | 0.06 |
| 2 | 1.9 | 1.2–2.9 | |
| 3 | 0.7 | 0.4–1.3 | |
| 4 | 1 | 0.7–1.4 | |
| 5 (highest) | 1.1 | 0.8–1.4 | |
| Maternity unit | 1.5 | 0.4–5.7 | |
| 1 | 1.33 | 0.97–1.82 | 0.11 |
| 2 | 0.99 | 0.71–1.36 | |
| 3 | 0.30 | 0.06–1.50 | |
| 4 | 1.85 | 1.11–3.09 | |
| 5 | 1.14 | 0.60–2.17 | |
| 6 | 0.78 | 0.48–1.26 | |
| 7 | 1.52 | 0.40–5.71 | |
| Parity | |||
| Nulliparous | 1.15 | 0.89–1.49 | |
| Multiparous | 1.07 | 0.84–1.37 | 0.69 |
| Maternal smoking in pregnancy | |||
| No | 1.11 | 0.93–1.33 | 0.59 |
| Yes | 1.42 | 0.59–3.43 | |
| Maternal BMI | |||
| ≤25 | 1.20 | 0.96–1.49 | |
| >25, ≤ 30 | 0.62 | 0.42–0.90 | <0.001 |
| >30 | 2.05 | 1.25–3.35 | |
| Multiple pregnancy | |||
| No | 1.11 | 0.93–1.33 | |
| Yes | 1.02 | 0.23–4.53 | 0.91 |
| Mode of birth | |||
| Vaginal | 1.02 | 0.81–1.28 | 0.67 |
| Instrumental | 1.26 | 0.76–2.09 | |
| Pre-labour caesarean | 1.29 | 0.82–2.05 | |
| Intrapartum caesarean | 1.27 | 0.80–2.02 | |
| Gestational age at birth (completed weeks) | |||
| <37 | 1.26 | 0.64–2.48 | |
| ≥37 | 1.10 | 0.92–1.32 | 0.70 |
| Infant gender | |||
| Male | 1.05 | 0.81–1.34 | |
| Female | 1.17 | 0.91–1.52 | 0.52 |
| Infant admission to intensive care or special care nursery | |||
| No | 1.11 | 0.92–1.35 | 0.83 |
| Yes | 1.06 | 0.68–1.65 |