Table 3

Associations between maternal smoking during pregnancy and infant birthweight by maternal GSTT1 and GSTM1 genotype assessed by the crude and adjusted coefficient ß in linear regression
Genotype Smoking status during pregnancy Birthweight, g Birthweight, g β+crude (SE) P Birthweight, g β++adjusted (SE) P Birthweight, g β++adjusted (SE) P
Total sample Non-smoking (n = 456) 3390.3 Referent Referent Referent
Smoking (n = 83) 3284.1 −86.5 (57.5) 0.066 −83.4 (57.1) 0.073 −83.4 (57.1) 0.073
GSTT1
Present Non-smoking (n = 385) 3401.4 Referent Referent Referent
Present Smoking (n = 61) 3320.7 −70.4 (65.7) 0.143 −72.3 (65.1) 0.134 −38.8 (57.6) 0.250
Null Non-smoking (n = 71) 3330.0 Referent Referent −22.6 (57.6) 0.345
Null Smoking (n = 22) 3182.9 −115.9 (129) 0.186 −123.7 (131) 0.175 −162.9 (93.0) 0.041
*Interaction: smoking × GSTT1-null −111.9 (123.1) 0.182 −96.8 (122.5) 0.215
GSTM1
Present Non-smoking (n = 242) 3413.6 Referent Referent Referent
Present Smoking (n = 49) 3255.9 −87.2 (73.9) 0.119 −85.1 (74.2) 0.126 −58.8 (66.1) 0.187
Null Non-smoking (n = 214) 3363.9 Referent Referent −32.4 (41.2) 0.216
Null Smoking (n = 34) 3324.8 −97.1 (92.0) 0.146 −100.6 (90.2) 0.133 −118.7 (79.6) 0.069
*Interaction: smoking ×GSTM1-null −17.0 (106.1) 0.437 −26.6 (105.6) 0.400
GSTT1 & GSTM1
Present Non-smoking n = 207) 3429.4 Referent Referent Referent
Present Smoking (n = 38) 3251.2 −137.9 (82.3) 0.048 −135.5 (82.6) 0.051 −84.7 (71.2) 0.118
Null Non-smoking (n = 36) 3339.7 Referent Referent 10.1 (76.1) 0.447
Null Smoking (n = 11) 3093.5 −318.0 (198) 0.058 −320.8 (203) 0.061 −311.2 (128) 0.008
*Interaction: smoking ×GSTT1–null ×GSTM1–null - 240.3 (164) 0.072 −234.5 (164.3) 0.078

ß represent the difference in mean birth weight for cigarette smoking between the variant genotype.

+ ß crude.

++ ß after adjustment for the covariates: gestational age, body mass index, education, family status, parity and blood pressure.

*Test of interaction: a P value is presented for testing the null hypothesis, ß = 0 in multiple linear regression models for the product term, smoking x genotypes.

Danileviciute et al.

Danileviciute et al. BMC Pregnancy and Childbirth 2012 12:161   doi:10.1186/1471-2393-12-161

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