In humans
In humans, retained placenta is generally defined as a placenta that has not undergone placental expulsion within 30 minutes of the baby’s birth where the third stage of labor has been managed actively.
Risks of retained placenta include hemorrhage and infection. After the placenta is delivered, the uterus should contract down to close off all the blood vessels inside the uterus. If the placenta only partially separates, the uterus cannot contract properly, so the blood vessels inside will continue to bleed. A retained placenta thereby leads to hemorrhage.
Management
There is no effective pharmacological treatment for retained placenta. It is useful ensuring the bladder is empty. However, ergometrine should not be given as it causes tonic uterine contractions which may delay placental expulsion. Controlled cord traction has been recommended as a second alternative after more than 30 minutes have passed after stimulation of uterine contractions, provided the uterus is contracted. Manual extraction may be required if cord traction also fails, or if heavy ongoing bleeding occurs. Very rarely a curettage is necessary to ensure that no remnants of the placenta remain (in rare conditions with very adherent placenta such as a placenta accreta).
However, in birth centers and attended home birth environments, it is common for licensed care providers to wait for the placenta's birth up to 2 hours in some instances.
In cattle
Retention of fetal membranes (afterbirth) is observed more frequently in cattle than in other animals. In a normal condition, a cow’s placenta is expelled within a 12-hour period after calving.