Maternal serum CA 125 levels in pregnancies with chromosomally-normal and -abnormal fetuses

We measured the maternal serum cancer antigen 125 (MS‐CA 125) levels in 98 nonpregnant women, 765 first‐ and second‐trimester pregnancies with chromosomally‐normal fetuses, and 54 chromosomally‐abnormal pregnancies. To determine the MS‐CA 125 concentration, we used a new automated microparticle enzyme immunoassay with low inter‐assay variability. The median MS‐CA 125 level decreased from the first to the second trimester of pregnancy and was higher than that in non‐pregnant women. We found no difference between normal and Down's syndrome (n = 29) pregnancies ( t‐test: t = 0·57, p >0·5). The MS‐CA 125 levels in pregnancies with other chromosomal abnormalities showed no difference either, compared with the normals. We conclude that MS‐CA 125 is not a useful marker for fetal Down's syndrome, nor for other chromosomal disorders in pregnancy.