Causes of prolonged pregnancy

There are some well-established, albeit fairly uncommon, causes of prolonged pregnancy. Pregnancies with abnormalities in the fetal hypothalamic-pituitary axis, such as anencephaly (4), and pregnan­cies complicated by the X-linked disease placental steroid sulphatase deficiency (5) are often prolonged. Also, those few extrauterine preg­nancies which succeed in obtaining a vascular supply from some­where in the pelvis and become an advanced abdominal pregnancy also typically fail to go into spontaneous labour.