Objective To determine the values and variation tendency of a disintegrin and metalloprotease 12-S(ADAM12-S)of early pregnancy, and discuss the value of ADAM12-S to the ectopic pregnancy in the first trimester.Methods 150 early pregnancy cases (from the 5th to 10th week of pregnancy)were selected in Huanggang Women &Children's Healthcare Hospital.There were 102 cases of normal pregnancy,48 cases of ectopic pregnancy.The AutoDELFIA immunoassay platform was used to measure the value of ADAM12-S in the serum.Results Of the 102 normal pregnancies, the values of ADAM12-S in 5th-10th week of pregnancy linearly increase with gestationalage.The correlation coefficient was 0.9217 (P<0.05).While the values of ADAM12-S in the ectopic pregnancy group were significantly lower than the normal pregnancy group and not linearly increased with gestationalage.The correlation coefficient was 0.2817.There was statistically significant difference between the two groups (P<0.05).Conclusion The values of ADAM12-S is stable in the first trimester of normal pregnancy,while it is much more lower in abnormal pregnancy.ADAM12-S has great significance in the diagnosis of ectopic pregnancy of the first trimester.