Diagrams schematically represent the porcine uteri of the nine dams included in the study. Fetuses were numbered starting with the fetus located next to the ovarian tip of the left uterine horn. L and R: left and right uterine horn, respectively. Each circle represents an individual fetus. F: female and M: male fetuses. "+" and "-" within the circles represent PRRSV-positive and -negative fetuses. Filled circles are female fetuses that were tested for the presence of male sex-determining region Y (SRY) in serum via PCR. Red and green circles are SRY-positive or -negative fetuses, respectively. Female fetuses with non-filled circles were not tested due to the lack of serum ▲: in these fetuses microchimeric cells were found. na: not available; due to mummification the determination of fetal gender and PRRSV infection status was not possible.