Estimates of effects of quitting smoking on log (birth weight)*
| Variable | Mean (g) | 95% CI | Pr(>|t|) |
| Intercept: baseline (40 weeks) | 3233.1 | 3206.7 to 3259.8 | <0.001 |
| Gestational age at birth, centred at 40 weeks | |||
| Each additional week past 40 | 156.8 | 151.0 to 162.7 | <0.001 |
| Squared | −12.6 | −13.2 to −12.4 | <0.001 |
| Smoking status at delivery compared with smoker throughout | |||
| Non-smoker | 259.6 | 241.8 to 277.7 | <0.001 |
| Quitter | 210.2 | 186.3 to 235.0 | <0.001 |
| Parity compared with second child | |||
| First child | −104.4 | −115.4 to −92.9 | <0.001 |
| Third or more | 22.3 | 7.7 to 37.2 | <0.005 |
| Ethnicity compared with white | |||
| Caucasian | −141.6 | −159.4 to −123.5 | <0.001 |
| SEP (based on IMD score) compared with middle three-fifths | |||
| Least deprived fifth | 27.8 | 14.4 to 41.1 | <0.001 |
| Most deprived fifth | −15.5 | −40.4 to 10.1 | 0.232 |
| BMI compared with recommended | |||
| Underweight (<20) | −116.7 | −146.5 to −86.4 | <0.001 |
| Overweight (25–29.9) | 79.5 | 65.7 to 93.2 | <0.001 |
| Obese (30+) | 134.5 | 119.3 to 150.3 | <0.001 |
| Sex of baby compared with female | |||
| Male | 129.0 | 117.0 to 141.5 | <0.001 |
22 826 valid cases included in model (39.5% cases with missing data excluded).
*Estimates are backtransformed to represent the actual change in birth weight of babies with 95% CI and statistical significance.
BMI, boy mass index; SEP, socioeconomic position (categories defined by fifths of Index of Multiple Deprivation (IMD) score).