Factors which was concerned to low birth weight: interdelivery interval < 24 months (OR= 0, 01; [0, 0 to 0, 1]); a previous history of low birth weight (OR= 8, 9; [4, 1 to 19, 4]); weight of mothers before pregnancy < 40 kg (OR= 0, 2; [0, 1 to 0, 5]); weight of prenancy < 9 kg (OR= 0, 3; [0, 2 to 0, 8]; mothers are sick in time of prenancy (OR= 0, 1; [0, 2 to 1, 0]; prenatal visits < 3 times (OR= 0, 6; [0, 5 to 3].