Table 5. The confounding effect of smoking on the association between maternal age and adverse pregnancy outcome.
| Maternal age 30–34 years | Maternal age 35–39 years | Maternal age 40+ years | ||||
| Outcomes | AdjustedaRR(95% CI) | AdjustedaRR(95% CI) +smoking | AdjustedaRR (95% CI) | AdjustedaRR (95% CI) +smoking | AdjustedaRR(95% CI) | AdjustedaRR (95% CI) +smoking |
| VSGA (5th percentile) | 0.89(0.82, 0.96) | 0.98(0.90, 1.06) | 0.99(0.90, 1.10) | 1.11(1.00, 1.22) | 1.20 (1.01, 1.43) | 1.33(1.11, 1.58) |
| VLGA (95th percentile) | 1.25(1.16, 1.34) | 1.17(1.08, 1.26) | 1.35(1.24, 1.47) | 1.26(1.16, 1.37) | 1.49(1.29, 1.72) | 1.39(1.21, 1.61) |
| Macrosomia | 1.25(1.11, 1.41) | 1.16(1.03, 1.31) | 1.20(1.04, 1.37) | 1.10(0.96, 1.27) | 1.36(1.07, 1.71) | 1.26(1.00, 1.59) |
| Emergency Caesarean deliveries | 1.27(1.21, 1.33) | 1.26(1.20, 1.33) | 1.40(1.32, 1.48) | 1.39(1.31, 1.48) | 1.77(1.61, 1.95) | 1.76(1.60, 1.94) |
| Elective Caesarean deliveries | 1.42(1.37, 1.48) | 1.40(1.35, 1.46) | 1.70(1.63, 1.78) | 1.68(1.61, 1.75) | 1.89(1.77, 2.02) | 1.86(1.74, 2.00) |
| Preterm delivery (<37 weeks) | 1.03(0.96, 1.10) | 1.08(1.01, 1.16) | 1.25(1.16, 1.36) | 1.32(1.22, 1.44) | 1.20(1.03, 1.39) | 1.26(1.08, 1.46) |
| Stillbirth | 1.32(1.04, 1.69) | 1.39(1.09, 1.78) | 1.41(1.05, 1.89) | 1.49(1.11, 2.00) | 2.03(1.28, 3.20) | 2.13(1.35, 3.37) |
aAdjusted for , parity, maternal BMI, social deprivation score and ethnicity; Highlighted estimates indicate a significant interaction test with p<0.05. VSGA (Very small-for-gestational age, <5th percentile); VLGA (Very-large-for-gestational age, >95th percentile).