Trend of low birth weight risk according to maternal and infant characteristics: results of multivariate regression analysis
| Prevalence ratio (PR) and 95% CIs | p interaction* | |||
|---|---|---|---|---|
| 1995–1999 | 2000–2006 PR (95% CI) | 2007–2014 PR (95% CI) | ||
| Crude | 1 | 1.083 (1.068 to 1.098) | 1.166 (1.150 to 1.182) | |
| Adjusted† | 1 | 1.119 (1.103 to 1.135) | 1.229 (1.103 to 1.235) | |
| Maternal‡ | ||||
| Portuguese | 1 | 1.128 (1.112 to 1.144) | 1.256 (1.236 to 1.274) | <0.001 |
| Non-Portuguese | 1 | 0.863 (0.809 to 0.921) | 0.833 (0.782 to 0.888) | |
| Maternal age (years)‡ | ||||
| ≤19 | 1 | 0. 958 (0.914 to 1.003) | 0.937 (0.889 to 0.989) | <0.001 |
| 20–34 | 1 | 1.151 (1.132 to 1.170) | 1.269 (1.248 to 1.291) | |
| ≥35 | 1 | 1.066 (1.026 to 1.106) | 1.199 (1.156 to 1.244) | |
| Parity‡ | ||||
| Primiparous | 1 | 1.130 (1.110 to 1.151) | 1.243 (1.219 to 1.267) | <0.001 |
| Multiparous | 1 | 1.098 (1.073 to 1.123) | 1.200 (1.172 to 1.228) | |
| Maternal education (years)‡ | ||||
| Primary | 1 | 1.114 (1.094 to 1.133) | 1.209 (1.186 to 1.232) | 0.034 |
| Secondary | 1 | 1.142 (1.105 to 1.181) | 1.230 (1.190 to 1.271) | |
| Tertiary | 1 | 1.102 (1.058 to 1.147) | 1.260 (1.213 to 1.310) | |
| Maternal employment status‡ | ||||
| Employed | 1 | 1.121 (1.100 to 1.141) | 1.248 (1.225 to 1.272) | <0.001 |
| Unemployed | 1 | 1.131 (1.066 to 1.200) | 1.209 (1.144 to 1.278) | |
| Others | 1 | 1.122 (1.094 to 1.150) | 1.190 (1.157 to 1.224) | |
| Infant sex‡ | ||||
| Male | 1 | 1.114 (1.091 to 1.138) | 1.209 (1.183 to 1.236) | 0.878 |
| Female | 1 | 1.122 (1.101 to 1.145) | 1.245 (1.221 to 1.271) | |
*p Value for the comparison of a model with and without the interaction term between the variable and time.
†Adjusted for maternal nationality, maternal age (years), parity, maternal education, maternal employment status and infant sex.
‡Adjusted for all other variables and an interaction term between the variable and time.