Placental expulsion
Encyclopedia
Placental expulsion occurs when the placenta
comes out of the birth canal after childbirth
. The period from just after the fetus is expelled until just after the placenta is expelled is called the third stage of labor.
Maternal blood loss is limited by contraction
of the uterus following birth of the placenta. Normal blood loss is less than 600 mL.
Active management routinely involves clamping of the umbilical cord
, often within seconds or minutes of birth. It may also involve giving oxytocin
via intramuscular injection, followed by cord traction to assist in delivering the placenta. The oxytocic agents augment uterine muscular contraction and the cord traction assists with rapid birth of the placenta. However, premature cord traction can pull the placenta before it has naturally detached from the uterine wall, resulting in hemorrhage.
A Cochrane database study suggests that blood loss and the risk of postpartum bleeding will be reduced in women offered active management of the third stage of labour. However, the use of ergometrine for active management was associated with nausea or vomiting and hypertension, and controlled cord traction requires the immediate clamping of the umbilical cord
.
A summary of the Cochrane study came to the results that active management of the third stage of labour, consisting of controlled cord traction, early cord clamping plus drainage, and a prophylactic oxytocic agent, reduced postpartum haemorrhage by 500 or 1000 mL or greater, as well as related morbidities including mean blood loss, incidences of postpartum haemoglobin becoming less than 9 g/dL, blood transfusion, need for supplemental iron postpartum, and length of third stage of labour. Although active management increased adverse effects such as nausea, vomiting, and headache, women were less likely to be dissatisfied.
Breastfeeding
soon after birth and massaging of the top of the uterus (the fundus
) causes uterine contractions that encourage birth of the placenta.
Although uncommon, in some cultures the placenta is kept and consumed by the mother over the weeks following the birth. This practice is termed placentophagy
.
is a placenta that doesn't undergo expulsion within a normal time limit. Risks of retained placenta include hemorrhage and infection. If the placenta fails to deliver in 30 minutes in a hospital environment, manual extraction may be required if heavy ongoing bleeding occurs, and very rarely a curettage
is necessary to ensure that no remnants of the placenta remain (in rare conditions with very adherent placenta, 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.
on the uterus after birth. This is known as placentophagy
. However, it has been observed in zoology that chimpanzees, with which humans share 94%–99% of genetic material, apply themselves to nurturing their offspring, and keep the fetus, cord, and placenta intact until the cord dries and detaches the next day.
The placenta exists in most mammals and some reptiles. It is probably polyphyletic
.
Studies on pigs indicate that the duration of placenta expulsion increases significantly with increased duration of farrowing.
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
comes out of the birth canal after childbirth
Childbirth
Childbirth is the culmination of a human pregnancy or gestation period with the birth of one or more newborn infants from a woman's uterus...
. The period from just after the fetus is expelled until just after the placenta is expelled is called the third stage of labor.
Physiology
It begins as a physiological separation from the wall of the uterus. The placenta is usually expelled within 15–30 minutes of the baby being born.Maternal blood loss is limited by contraction
Contraction (childbirth)
-Throughout menstrual cycle:The uterus frequently contracts throughout the entire menstrual cycle, and these contractions have been termed endometrial waves or contractile waves. These appear to involve only the sub-endometrial layer of the myometrium...
of the uterus following birth of the placenta. Normal blood loss is less than 600 mL.
Management
The third stage of labor can be managed actively, or it can be managed expectantly (also known as physiological management or passive management), the latter allowing the placenta to be expelled without medical assistance.Active management routinely involves clamping of the umbilical cord
Umbilical cord
In placental mammals, the umbilical cord is the connecting cord from the developing embryo or fetus to the placenta...
, often within seconds or minutes of birth. It may also involve giving oxytocin
Oxytocin
Oxytocin is a mammalian hormone that acts primarily as a neuromodulator in the brain.Oxytocin is best known for its roles in sexual reproduction, in particular during and after childbirth...
via intramuscular injection, followed by cord traction to assist in delivering the placenta. The oxytocic agents augment uterine muscular contraction and the cord traction assists with rapid birth of the placenta. However, premature cord traction can pull the placenta before it has naturally detached from the uterine wall, resulting in hemorrhage.
A Cochrane database study suggests that blood loss and the risk of postpartum bleeding will be reduced in women offered active management of the third stage of labour. However, the use of ergometrine for active management was associated with nausea or vomiting and hypertension, and controlled cord traction requires the immediate clamping of the umbilical cord
Umbilical cord
In placental mammals, the umbilical cord is the connecting cord from the developing embryo or fetus to the placenta...
.
A summary of the Cochrane study came to the results that active management of the third stage of labour, consisting of controlled cord traction, early cord clamping plus drainage, and a prophylactic oxytocic agent, reduced postpartum haemorrhage by 500 or 1000 mL or greater, as well as related morbidities including mean blood loss, incidences of postpartum haemoglobin becoming less than 9 g/dL, blood transfusion, need for supplemental iron postpartum, and length of third stage of labour. Although active management increased adverse effects such as nausea, vomiting, and headache, women were less likely to be dissatisfied.
Breastfeeding
Breastfeeding
Breastfeeding is the feeding of an infant or young child with breast milk directly from female human breasts rather than from a baby bottle or other container. Babies have a sucking reflex that enables them to suck and swallow milk. It is recommended that mothers breastfeed for six months or...
soon after birth and massaging of the top of the uterus (the fundus
Fundus (uterus)
The fundus of the uterus is the top portion, opposite from the cervix.Fundal height, measured from the top of the pubic bone, is routinely measured in pregnancy to determine growth rates...
) causes uterine contractions that encourage birth of the placenta.
Although uncommon, in some cultures the placenta is kept and consumed by the mother over the weeks following the birth. This practice is termed placentophagy
Placentophagy
Placentophagy is the act of mammals eating the placenta of their young after childbirth.The placenta contains high levels of prostaglandin which stimulates involution of the uterus, in effect cleaning the uterus out...
.
Retained placenta
A retained placentaRetained placenta
Retained placenta is a condition where all or part of the placenta or membranes are left behind in the uterus during the third stage of labour.-In humans:...
is a placenta that doesn't undergo expulsion within a normal time limit. Risks of retained placenta include hemorrhage and infection. If the placenta fails to deliver in 30 minutes in a hospital environment, manual extraction may be required if heavy ongoing bleeding occurs, and very rarely a curettage
Curettage
Curettage, in medical procedures, is the use of a curette to remove tissue by scraping or scooping.Curettages are also a declining method of abortion. It has been replaced by vacuum aspiration over the last decade....
is necessary to ensure that no remnants of the placenta remain (in rare conditions with very adherent placenta, placenta accreta
Placenta accreta
Placenta accreta is a severe obstetric complication involving an abnormally deep attachment of the placenta, through the endometrium and into the myometrium...
. 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.
Non-humans
In most mammalian species, the mother bites through the cord and consumes the placenta, primarily for the benefit of prostaglandinProstaglandin
A prostaglandin is any member of a group of lipid compounds that are derived enzymatically from fatty acids and have important functions in the animal body. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring....
on the uterus after birth. This is known as placentophagy
Placentophagy
Placentophagy is the act of mammals eating the placenta of their young after childbirth.The placenta contains high levels of prostaglandin which stimulates involution of the uterus, in effect cleaning the uterus out...
. However, it has been observed in zoology that chimpanzees, with which humans share 94%–99% of genetic material, apply themselves to nurturing their offspring, and keep the fetus, cord, and placenta intact until the cord dries and detaches the next day.
The placenta exists in most mammals and some reptiles. It is probably polyphyletic
Polyphyly
A polyphyletic group is one whose members' last common ancestor is not a member of the group.For example, the group consisting of warm-blooded animals is polyphyletic, because it contains both mammals and birds, but the most recent common ancestor of mammals and birds was cold-blooded...
.
Studies on pigs indicate that the duration of placenta expulsion increases significantly with increased duration of farrowing.