Table 4.

Joint association of maternal cigarette smoking during pregnancy, CYP1A1 and GSTT1 gene polymorphisms with preterm subgroups

Smoking	CYP1A1	GSTT1	Total subjects	%	OR (95% CI)	P	Adjusted P
Spontaneous PTD
Never	AA	Present	506	22.3a	Ref
Never	AA	Absent	166	21.1a	0.9 (0.6–1.4)	0.71	0.90
Never	Aa/aa	Present	412	22.8a	1.1 (0.8–1.5)	0.62	0.86
Never	Aa/aa	Absent	125	27.2a	1.4 (0.9–2.2)	0.15	0.35
Persistent	AA	Present	104	37.5a	1.7 (1.0–2.8)	0.04	0.15
Persistent	AA	Absent	40	32.5a	1.2 (0.6–2.5)	0.65	0.88
Persistent	Aa/aa	Present	63	41.3a	2.0 (1.1–3.5)	0.02	0.10
Persistent	Aa/aa	Absent	18	72.2a	8.3 (2.7–30.6)	4 × 10−4 *	0.01
Interaction					4.4 (0.9–21.8)	0.07	0.21
Very PTD (<32 weeks)
Never	AA	Present	438	10.3b	Ref
Never	AA	Absent	138	5.1b	0.4 (0.2–0.9)	0.05	0.17
Never	Aa/aa	Present	347	8.4b	0.8 (0.5–1.4)	0.52	0.81
Never	Aa/aa	Absent	106	11.7b	1.3 (0.6–2.5)	0.48	0.77
Persistent	AA	Present	79	17.7b	1.6 (0.7–3.3)	0.27	0.55
Persistent	AA	Absent	30	10.0b	0.7 (0.2–2.4)	0.65	0.88
Persistent	Aa/aa	Present	43	14.0b	1.1 (0.4–3.0)	0.82	0.95
Persistent	Aa/aa	Absent	12	58.3b	11.1 (2.9–47.7)	6 × 10−4 *	0.01
Interaction					10.8 (2.5–51.4)	2 × 10−3 *	0.03
PTD accompanied by histologic chorioamnionitis
Never	AA	Present	413	10.9c	Ref
Never	AA	Absent	129	10.1c	0.9 (0.5–1.8)	0.87	0.96
Never	Aa/aa	Present	328	10.7c	1.0 (0.6–1.6)	0.99	0.99
Never	Aa/aa	Absent	97	10.3c	0.9 (0.4–1.9)	0.81	0.95
Persistent	AA	Present	77	23.4c	2.2 (1.1–4.3)	0.03	0.12
Persistent	AA	Absent	35	22.9c	1.9 (0.7–4.7)	0.16	0.36
Persistent	Aa/aa	Present	40	12.5c	1.1 (0.3–2.8)	0.92	0.97
Persistent	Aa/aa	Absent	12	66.7c	15.6 (4.1–76.7)	2 × 10−4 *	0.01
Interaction					18.6 (2.1–162.7)	8 × 10−3	0.06

Logistic regression was performed with adjusting covariates: maternal age, ethnicity, education, parity, marital status, maternal pre-pregnant BMI, alcohol use, passive smoke exposure, illicit drug use and infant sex

^*P values with asterisk sign are the ones retaining statistical significance after multiple-testing correction

^aPercentage of subjects with spontaneous PTD

^bPercentage of subjects with very PTD

^cPercentage of subjects with PTD and histologic chorioamnionitis