We welcome the comments of Scopelitis and colleagues and apologize for misquoting their abstract [1]. Although both studies [2, 3] reach similar conclusions regarding the association of elevated IgG anticardiolipin antibodies and fetal loss, they differ in the choice of study population, timing of anticardiolipin antibody determination, and the quantitative measure of these antibodies associated with fetal loss. Perez and colleagues [2] studied the prevalence of the antibodies in 1200 unselected, pregnant, African-American women. An elevated antibody level was found in 1.25%. In contrast, we prospectively studied a low-risk, predominantly white population [3]. We found an elevated antibody level in 4.64% of patients based on samples drawn at the first prenatal visit. It is interesting that, despite the difference in racial composition, both studies showed that an elevated IgG anticardiolipin antibody level confers an increased risk for fetal loss.

The timing of the anticardiolipin antibody sample may explain the difference in the percentage of patients positive for the antibody. The mean gestational age of our prenatal sample was 13.5 weeks compared with 18.9 weeks (overall mean) for patients in the New Orleans study. We have shown that the number of patients positive for the anticardiolipin antibody can change between the first prenatal visit and delivery. Although 4.64% of our patients were positive for IgG anticardiolipin antibody at the first prenatal visit (< 25 weeks gestation), only 2.14% of patients had an elevated antibody level at the time of delivery.

Perez and colleagues compared the case records of the 15 women who were positive for IgG anticardiolipin antibody with the case records of 393 women from their original cohort who were negative for the antibody. They found the greatest prevalence of fetal loss in the 6 women who had moderate to high antibody levels. In contrast, the fetal losses in our patients who were positive for the antibody were all in patients with antibody levels in the low-positive range, and most fetuses had not reached 20 weeks gestation. It is possible that Perez and colleagues may have unintentionally excluded women with early fetal loss and lower antibody levels, given that almost 70% of the antibody determinations in their group were done after the first trimester.