NGF and spontaneous abortion: The ratio of proNGF to mature NGF may also play a similar role to that in neurodegenerative disorders as outlined above, but likely is responsible for the breakdown of uterine sympathetic nerves during gestation, and the re-innervation of uterine nerves during postpartum recovery44,45, and unbalanced NGF distribution in placental tissue is associated with miscarriages in humans46.