Lyrenäs , Sven, Fred Nyberg, Gunilla Willdeck-Lund, Leif Lindström, Bo Lindberg, and Lars Terenius. 1987. “Endorphin Activity in Cerebrospinal Fluid Prior to Elective Cesarean Section and in Early Puerperium”. Upsala Journal of Medical Sciences 92 (1):37-45. https://doi.org/10.3109/03009738709178676.