Objective-To determine the effects of maternal age, parity and fetal sex on amniotic fluid (AF) and maternal serum (MS) levels of CA 125, CA 19.9, CA 15.3 and carcinoembryonic antigen (CEA). Subjects and Setting-MS samples for CA 125, CA 19.9, CA 15.3 and CEA assay were obtained from 62 pregnant women at 16-20 weeks of gestation. AF was obtained from the same patients during genetic amniocentesis. Methods-Radioimmuno assay to determine tumor marker concentrations. Results-The following statistically significant differences were observed: (1) MS CA 19.9 and CA 15.3 values were elevated in the primigravida group. MS mean CA 19.9 value was also abnormally elevated. (2) MS mean CA 19.9 and CEA values and AF mean CA 19.9 value were elevated in the female fetus group. Conclusions-Parity and fetal sex were associated with AF and MS levels of some tumor markers. Therefore, to prevent misinterpretation of the tumor marker values during pregnancy further investigation is needed to find normal values for each trimester, paying particular attention to parity and fetal sex.