PROS1 and Abnormality of the uterus: The following were the incidences of risk factors for 462 women with RPL: uterine malformation, 5.4%; thyroid dysfunction, 14.8%; chromosomal abnormality in women with RPL and their spouses, 3.0%; aPL positivity, 14.7%; low factor XII activity, 8.5%; low protein C activity, 2.2%; low protein S activity, 13.4%; and unexplained, 53.0%.