Table 1.

Distributions of selected characteristics in participants with normal birth weight (NBW) and low birth weight (LBW).

Characteristics	NBW (n = 8581)		LBW (n = 650)		P -value
	n	%	n	%
Maternal age
<25	1919	22.36	195	30.00	<0.001
25 29	3630	42.31	196	30.15
≥30	3032	35.33	259	39.85
Monthly income per capita(RMB)
<3000	4233	54.56	436	73.90	<0.001
≥ 3000	3525	45.44	154	26.10
Missing	823		60
Maternal education level
< College	5131	60.89	516	81.52	<0.001
≥ College	3295	39.11	117	18.48
Missing	155		17
Smoking (passive and active)
No	6923	80.68	489	75.23	<0.001
Yes	1658	19.32	161	24.77
Drink during pregnancy
No	8564	99.80	648	99.69	0.391*
Yes	17	0.20	2	0.31
Maternal employ
No	4050	47.20	409	62.92	<0.001
Yes	4531	52.80	241	37.08
Pre-pregnancy BMI (kg/m2)
<18.5	1821	21.92	135	22.13	0.078
18.5 23.9	5644	67.93	396	64.92
≥24.0	843	10.15	79	12.95
Missing	273		40
Weight gain during pregnancy (kg)
<15	2542	30.75	346	59.04	<0.001
15 18.5	2753	33.30	132	22.53
> 18.5	2972	35.95	108	18.43
Missing	314		64
Preeclampsia
No	8382	97.68	535	82.31	<0.001
Yes	199	2.32	115	17.69
Parity
Primipara	6310	73.53	374	57.54	<0.001
Multipara	2271	26.47	276	42.46
Cesarean section
No	5428	63.98	290	47.08	<0.001
Yes	3056	36.02	326	52.92
Missing	97		34
Gender of live birth
Male	4427	51.69	326	50.31	0.498
Female	4138	48.31	322	49.69
Missing	16		2
Preterm
No	8177	95.29	153	23.54	<0.001
Yes	404	4.71	497	76.46

Calculated by χ² analysis without accounting for missing data.

^*Fisher's exact test.