Table 2. ROP's circumstances with different birth weight.

ROP	≤1000g	1001-1500g	1501-2000g	2001-2500g
Non-ROP	9(36.0)	70(76.1)	185(92.0)	243(97.2)
ROP1	8(32.0)	8(8.7)	8(4.0)	4(1.6)
ROP2	4(16.0)	6(6.5)	6(3.0)	3(1.2)
ROP3	3(12.0)	5(5.4)	2(1.0)	0(0.0)
ROP4	1(4.0)	1(1.1)	0(0.0)	0(0.0)
ROP5	0(0.0)	2(2.2)	0(0.0)	0(0.0)
Total	25(100)	92(100)	201(100)	250(100)

P<0.05

n(%)