Cause of post-term pregnancy is usually unknown, but a previous post-term pregnancy increases the risk by 2-3 times. Post-term pregnancy can be caused by disorders affecting the fetal pituitary-adrenal system (e.g., anencephaly, adrenal hypoplasia, congenital adrenal hyperplasia) and X-linked ichthyosis associated with placental sulfatase deficiency. In most cases, fetal growth continues until birth. However, in some cases, placental involution (as pregnancy progresses) and multiple infarcts are observed, as well as villous degeneration, leading to placental insufficiency syndrome. As a result, the fetus receives inadequate nutrients and oxygen from the mother, resulting in a thin (due to soft tissue depletion), malnourished infant with depleted glycogen stores and reduced amniotic fluid volume. Such infants are considered premature and, depending on the onset of placental insufficiency and the severity of the condition, may be small for gestational age. Although, placental insufficiency with impaired maturation can occur at any gestational age, it most often occurs after 41-42 weeks of pregnancy.