Dear Editor,rnFetuses develop antibodies when they are infected with porcine circovirus type 2 (PCV2).At abortion or birth,both PCV2 and/or anti-PCV2 antibodies can then be detected.Finding anti-PCV2 antibodies in aborted fetuses or stillb piglets is generally used as evidence of an intra-uterine PCV2 infection.However,a recent analysis of fetuses sent in for PCV2 diagnosis and caesarean-derived,colostrum-deprived pigs revealed that low anti-PCV2 antibody titers (10-640) were found without detecting PCV2 itself.These findings suggest that small amounts of anti-PCV2 antibodies are able to cross the placenta.To provide further evidence for this hypothesis,anti-PCV2 antibody status was measured in piglets b from sows with high antibody titers (40,960-655,360) before colostrum uptake.We found that 60％,27％,and 12％ of the piglets from sows with titers of 655,360,163,840,and 40,960,respectively,had low anti-PCV2 antibody titers (10-160).An intra-uterine PCV2 infection was excluded by the absence of PCV2 in the sera of both piglets and sows.These results indicated that antibody leakage occurred and correlated with the antibody titer of the sow.Our findings demonstrate that care needs to be taken when diagnosing an intra-uterine PCV2 infection based on antibody detection.