Pre-term labor and placental abnormalities (such as placental abruption, in which the placenta separates from the uterus) are increased roughly twofold among women who undergo assisted-reproductive procedures than those who get pregnant naturally, and children conceived using these technologies are about twice as likely to be born prematurely and to be underweight at birth. To reduce the likelihood of multiple pregnancies, the Society of Assisted Reproductive Technology and the American Society for Reproductive Medicine have established guidelines for the number of fertilized embryos to be transferred to the uterus during a cycle of infertility treatment.