Lyrenäs Sven, Nyberg Fred, Willdeck-Lund Gunilla, Lindström Leif, Lindberg Bo, and Terenius Lars. 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.