Most cases affect preterm birth infants and result from placental insufficiency and/or fetal hypoxia. Another important vertebrate syncytium is in the placenta of placental mammals. The risk of placental abruption increases sixfold after severe maternal trauma. However, bandicoots also have a rudimentary chorioallantoic placenta, similar to those of placental mammals. This is produced in the trophoblast cells of the placental tissue. Marsupial reproductive organs differ from the placental mammals. The cause of placental abruption is not entirely clear. It is used in ultrasound testing of umbilical artery for placental insufficiency. Both methods offer the option of fetal and placental testing. Marsupials' reproductive systems differ markedly from those of placental mammals. Many hormones can induce insulin resistance including cortisol, growth hormone, and human placental lactogen. The spermatozoa of marsupials are usually longer than those of placental mammals. In marsupial and placental mammals, copulation occurs through the vagina. Pre-natal development differs between marsupials and placental mammals. AS can be the cause of menstrual disturbances, infertility, and placental abnormalities.