Illustration of a female abdomen with a hand inserted through the vagina (birth canal) to the uterus (womb) to extract a retained placenta (red) caused by an hour-glass contraction of the uterus. The placenta is a temporary organ that connects a developing foetus to its mother. The placenta carries oxygen and nutrients to the foetus and removes waste products. A retained placenta is one that has not been delivered 30 minutes after childbirth. If not removed it can cause life-threatening blood loss or severe infection. From An Improved System of Midwifery, by Wooster Beach (1794-1868), published in 1851.