Mechanism and clinical significance of elevated CA 125 levels in the sera of pregnant women.

To clarify the mechanism of CA 125 elevation in maternal sera, serum levels of CA 125 and CA 19-9 were measured in 122 apparently healthy pregnant women (fifth to fortieth week of gestation) and 50 postpartum women (26 term deliveries and 24 second-trimester induced abortions). Serum levels of CA 125 showed an initial increase by the tenth week and then decreased to less than 35 U/ml, remaining below this level until delivery. However, within 1 hour after term delivery or second-trimester induced abortion, the CA 125 levels showed a second increase and decreased rapidly thereafter. In contrast, serum levels of CA 19-9 did not change significantly during these periods. Combined with our previous finding that the decidua contains abundant CA 125 but little CA 19-9, these results indicate that the elevated CA 125 levels in maternal sera originate from the decidual cells affected by chorionic invasion or the placental separation.