Longitudinal measurement of anticardiolipin antibodies during normal pregnancy: a prospective study.

We have previously shown that elevation of anticardiolipin antibodies (aCL) at the first prenatal visit is associated with increased fetal loss in normal pregnancy. The variation in aCL levels during normal pregnancy has not been established. To examine this question we measured IgG, IgM and IgA aCL levels five times during pregnancy at weeks 5-15, 16-25, 26-35, 36-37 and at delivery. Data were analyzed to determine: (a) the within and between subject variability of aCL during pregnancy; (2) the temporal trend of aCL; and (3) the relation of serial measures of aCL with maternal complications of pregnancy. We divided our cohort of 354 subjects into two groups. Group A included those subjects with consistently normal levels of aCL and group B those subjects with at least one elevated level of aCL. In group A the within subject variability was relatively low (28-34%). In group B we found wide fluctuations in aCL levels and a within subject variability of 88-91%. Subjects in group B had no increase in maternal complications of pregnancy. The present data suggest that aCL may fluctuate significantly during normal pregnancy and there is little clinical value in measuring aCL on a serial basis during pregnancy.