Six hundreds and thirty six women with normal pregnancy from 7th to 12th week were selected into controls. Results: Risk factors for hydatidiform mole included: 1) maternal age ≤ 20 (OR * =2; 95% CI=1.2 - 3.4 p=0.01); 2) maternal age ≥ 40 (OR * =3; 95% CI=1.5 - 6.1 p=0.002); 3) Low income (OR * =2; 95% CI=1.3 - 3.1 p=0.001); 4) Never used any contraceptive methods (OR * =2.4; 95% CI=1.6 - 3.5 p=0.000); 5) Unwanted pregnancy (OR * =3; 95% CI=1.9 - 4.9 p=0.000).