Table 1.

Characteristics of study population.

	Maternal smoking status
	All (n = 291)	Never-smokers (n = 124)	Stopped smokers before pregnancy (n = 44)	Stopped smokers after confirming pregnancy (n = 77)	Sustained smokers during pregnancy (n = 46)	P value (among 4 groups)	P-value (Never-smokers vs sustained-smokers)
Mothers
Maternal Age (years)	30.1 ± 5.0	30.7 ± 4.9	31.1 ± 4.0	29.0 ± 5.0	29.1 ± 5.5	0.033*	0.076
Maternal BMI before pregnancy (kg/m2)	20.9 ± 2.9	20.8 ± 2.9	20.7 ± 1.6	21.1 ± 3.3	20.9 ± 3.2	0.835	0.865
Parity
0	150 (51.5)	66 (53.2)	15 (34.1)	47 (61.0)	22 (47.8)	0.036*	0.531
≥1	141 (48.5)	56 (46.8)	29 (65.9)	30 (39.0)	24 (52.2)
Maternal Educational level (years)
≤12	131 (45.0)	54 (36.3)	20 (45.5)	37 (48.1)	29 (63.0)	0.017*	0.002**
>12	160 (55.0)	79 (63.7)	24 (54.5)	40 (51.9)	17 (37.0)
Partner’s smoking status
Mothers with partners of never smokers	44 (15.1)	27 (21.8)	8 (18.2)	7 (9.1)	2 (4.3)	0.001**	0.003**
Mothers with partners of stopped smoking before pregnancy	35 (12.0)	21 (16.9)	8 (18.2)	3 (3.9)	3 (6.5)
Mothers with partners of stopped smoking after confirming pregnancy	4 (1.4)	3 (2.4)	0 (0.0)	1 (1.3)	0 (0.0)
Mothers with partners of sustained smoking during pregnancy	207 (71.1)	73 (58.9)	28 (63.6)	66 (85.7)	40 (87.0)
Unknown	1 (0.3)	0 (0.0)	0 (0.0)	0 (0.0)	1 (2.2)
Infants
Sex
Male	131 (45.0)	52 (41.9)	27 (61.4)	36 (46.8)	16 (34.8)	0.064	0.398
Female	160 (55.0)	72 (58.1)	17 (38.6)	41 (53.2)	30 (65.2)
Gestational age (weeks)	39.4 ± 1.0	39.3 ± 1.1	39.3 ± 1.2	39.5 ± 0.9	39.5 ± 1.0	0.225	0.221
Birth weight (g)	3129.2 ± 332.7	3111.3 ± 324.8	3099.9 ± 382.3	3176.8 ± 339.3	3130.2 ± 292.2	0.519	0.729

n (%) or mean ± standard deviation. ANOVA, independent t-test and chi-squared test.

*P < 0.05; **P < 0.01; ***P < 0.001.