01/26/2025
The birth of the placenta is part of a complex process that begins before the baby is born. Oxytocin is released by the posterior pituitary gland during labor to regulate contractions. It is a key birthing/bonding hormone and plays a significant role in facilitating effective contractions. As the birth of the baby nears, high levels of oxytocin circulate in the mother’s blood which create strong uterine contractions. After the birth of the baby, the contraction pattern is interrupted because the uterus is suddenly emptied and must contract down to its pre-pregnancy size. The placenta drains its full blood volume to the baby which reduces its overall volume.
After a resting phase of about two minutes, contractions should resume and come every three to four minutes.[1] Anne Frye has observed, “The uterus generally has resting-phase contractions for about twice as long as the length of time between the final pushing contractions before birth. For example, if the last several pushing contractions were about five minutes apart, expect the first noticeable ‘placental’ contraction to occur about ten minutes after birth.”[2] The post birth contractions allow the uterus to further contract to expel the placenta, and after that, to reposition and reconstitute the uterus to its pre-pregnancy size. The first of these contractions will dislodge the placenta from its attachment site in the uterine wall. This happens as the eight- to ten-inch surface area of the uterine-placental attachment reduces in size by creating multiple folds, while the size of the placenta stays the same.[3] As the placenta sheers away from the uterus, the blood vessels of this highly vascular organ are exposed. The mother will bleed between the time that the placental attachment site is exposed and when contractions have shrunk the surface area of the uterus enough to suture off the exposed vessels. This is the only point in birth when blood is a part of the normal physiology and not an indication of complication.
Instinctive mother-baby interactions stimulate further oxytocin release and thus resulting in additional contractions.
These interactions involve smell, touch (skin-to-skin), taste, and sound. Breastfeeding immediately after the baby is born also increases oxytocin. If allowed to, the baby ‘crawls’ on the mother’s abdomen in order to nurse; his feet will stimulate her uterus to contract. The placenta is thus compressed, and the blood in the intervillious spaces (the interface between mother’s blood system and the placenta/baby’s blood system) is forced back into the spongy layer of the decidua (uterine lining). Retraction of the uterine muscle fibers constrict the blood vessels supplying the placenta, preventing blood from draining back through the maternal vascular tree. This congestion results in the veins rupturing and the villi shearing off the uterine wall. A clot forms behind the placenta. The non-elastic placenta is unable to remain attached and peels away, usually starting from the middle. At this point, you may notice a small gush of blood as the placenta separates and the umbilical cord lengthens as the placenta moves downwards and is birthed.
[1] Dunn P. “The Placental Venous Pressure During and After the Third Stage Of Labor Following Early Cord Ligation.” Journal of Obstetrics and Gynecology of The British Commonwealth, 73(5); 747-756, 1966
[2] Frye, Anne. Holistic Midwifery: A Comprehensive Textbook for Midwives In Homebirth Practice. Vol II. Labrys Press, 2006, pp 509
[3] Yao Ac, Et Al. “Placental Transfusion-Rate and Uterine Contraction.” Lancet, 1(7539) 1968, pp 380-3.