Objective To establish the adjusted value for multiple of the median (MOM) of a disintegrin and metalloprotease 12-secreting-type (ADAM12-S) in prenatal serum screening for Down′s syndrome. Methods The parturients, who were voluntary participants of prenatal screening program for Down′s syndrome during 2008 and were confirmed to labor healthy newborn by followup visit, were randomly enrolled in this study. Totally 577 serum samples of the first trimester (from 8 to 13 weeks) were collected and the concentration of ADAM12-S was determined by timeresolved fluorimmunoassay (TRFIA). The regressive relationship between concentration of ADAM12-S and gestational age was analyzed with SPSS 15.0 software and then the optimal model was selected for the calculation of MOM value of ADAM12-S. The MOM value was adjusted on the basis of the body weight of parturients. The curve fitting of ADAM12-S concentration and the adjusted MOM value were conducted and the model was optimized for the equation by eliminating the influence of gestational age and body weight. Results A positive correlation between the MOM value of ADAM12-S (Y) and gestational age (t) was shown, and the equation was Y=e^{8.412-24.534/t}, while a negative correlation between MOM value of ADAM12-S (Y) and body weight of parturients (z) was found, and the equation was Y=1.603*e^-0.009*z. The equation of concentration of ADAM12-S (Y) and the adjusted MOM value (X) was Y=0.036*X^0.552. Conclusions The equation between the initial concentration of ADAM12-S and the adjusted MOM value was established. It should be considerably important for the screening program of Down′s syndrome in primary clinical hospital for newborn.