Table 3. Interaction between maternal passive smoking during pregnancy and single genotype of CYP1A1 and GSTs on risk of spontaneous PTD.

Passivesmoking	Genotype	Case(n = 198)	Control(n = 524)	ORa(95%CI)	P-value
		N.(%)	N.(%)
	CYP1A1 Msp I
No	TT	41 (20.7)	151 (28.8)	1
No	TC/CC	60 (30.3)	218 (41.6)	0.96 (0.61–1.52)	0.876
Yes	TT	32 (16.2)	61 (11.6)	1.75 (1.00–3.07)*	0.052
Yes	TC/CC	65 (32.8)	94 (17.9)	2.42 (1.50–3.89)*	0.000
Interaction				1.44 (0.71–2.92)	0.319
	CYP1A1 BsrD I
No	AA	50 (25.3)	203 (38.7)	1
No	AG/GG	51 (23.5)	166 (31.7)	1.18 (0.75–1.85)	0.483
Yes	AA	45 (22.7)	87 (16.6)	1.98 (1.22–3.22)*	0.007
Yes	AG/GG	52 (26.3)	68 (13.0)	2.90 (1.78–4.72)*	0.000
Interaction				1.24 (0.62–2.47)	0.541
	GSTM1
No	Present	49 (24.7)	195 (37.2)	1
No	Null	52 (26.2)	174 (35.7)	1.15 (0.73–1.81)	0.519
Yes	Present	48 (24.2)	80 (15.3)	2.30 (1.41–3.74)	0.001
Yes	Null	49 (24.7)	75 (29.5)	2.43 (1.49–3.97)	0.000
Interaction				0.92 (0.46–1.83)	0.806
	GSTT1
No	Present	49 (24.7)	163 (31.1)	1
No	Null	52 (26.2)	206 (39.3)	0.84 (0.53–1.33)	0.454
Yes	Present	46 (23.2)	78 (14.9)	1.81 (1.10–2.98)	0.020
Yes	Null	51 (25.8)	77 (14.7)	2.22 (1.37–3.62)	0.002
Interaction				1.46 (0.73–2.91)	0.286
	GSTs
No	Present	73 (36.9)	267 (51.0)	1
No	Null	28 (14.1)	102 (19.5)	1.00 (0.60–1.66)	0.999
Yes	Present	64 (32.3)	119 (22.7)	1.86 (1.24–2.81)	0.003
Yes	Null	33 (16.7)	36 (6.9)	3.39 (1.95–5.91)	0.000
Interaction				1.83 (0.84–3.96)	0.126

^a.OR^a adjusted for family income, maternal age, education level and prepregnancy BMI.

^b.GSTs “null” if both GSTM1 and GSTT1 “null”, GSTs “present” if either GSTM1 or GSTT1 “present”.

^c.% for distribution within the case and control groups respectively.