Table 2.

The characteristics of the participates and the excluded.

Variables	Participants（n=605）	Excluded （n=195）	χ2	P
Age (years)			1.253	0.535
<30	289	93
30-34	226	67
≥35	90	35
Weeks of gestation (week)			0.304	0.323
<28	199	60
≥28	406	135
Chronic diseases			1.569	0.136
No	560	175
Yes	45	20