Placental expulsion (also called afterbirth) occurs when the

placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...

comes out of the

birth canal In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hyme ...

after

childbirth Childbirth, also known as labour and delivery, is the ending of pregnancy where one or more babies exits the internal environment of the mother via vaginal delivery or caesarean section. In 2019, there were about 140.11 million births glob ...

. The period from just after the baby is expelled until just after the placenta is expelled is called the third stage of labor. The third stage of labor can be managed actively with several standard procedures, 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. 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, also known as placentophagia, is the act of consuming part or all of the afterbirth following parturition in mammals. Parturition involves the delivery of the neonate, as well as the placenta and fetal membranes. The placenta is ...

Physiology

Hormone induction of placental separation

As the fetal hypothalamus matures, activation of the HPA axis (hypothalamic-pituitary-adrenal axis) initiates labour though two hormonal mechanisms. The end pathway of both mechanisms leads to contractions in the myometrium, a mechanical cause of placental separation, which is due to the shear force and contractile & involution changes that occur within the uterus distorting the placentome.

Fetal ACTH

ACTH Adrenocorticotropic hormone (ACTH; also adrenocorticotropin, corticotropin) is a polypeptide tropic hormone produced by and secreted by the anterior pituitary gland. It is also used as a medication and diagnostic agent. ACTH is an important c ...

increases fetal cortisol, which acts by two mechanisms: * Increases Prostaglandin F2α, which both abolishes the progesterone block, and lowers the oxytocin receptor threshold; and increases expression of relaxin, stretching the pelvic ligaments * Increases expression of PTGS in the fetal trophoblast cells PTGS in turn produces prostaglandin E2, which is a catalyst for pregnenolone to C-19 steroids, such as estrogen. Estrogen increases: * Vaginal lubrication * Softening of collagen fibre structures in the cervix, vaginal, and associated tissues * Increases contraction associated proteins (i.e. connexins) * Placental shedding by physiological inflammation, note pathological inflammation often leads to retention of membranes (i.e. placentitis)

Fetal oxytocin

As the HPA axis activates, the posterior pituitary of the fetus begins to increase production of oxytocin, which stimulates the maternal myometrium to contract.

Cellular changes of placental separation

In the seventh month of pregnancy the MHC-I complexes increase in the interplacentomal arcade reduces the bi- and tri-nucleate cells, a source of immune suppression in pregnancy. By the ninth month the endometrial lining has thinned (due to loss of trophoblast giant cells) which exposes the endometrium directly to the fetal trophoblast epithelium. With this exposure and the increase in maternal MHC-I, T-helper 1 (Th1) cells, and macrophages induce apoptosis of trophoblast cells and endometrial epithelial cells, facilitating placental release. Th1 cells attract an influx of phagocytic leukocytes into the placentome at separation, allowing further degration of the extracellular matrix.

Vascular changes of placental separation

After delivery, loss of fetal blood return to the placenta allows for shrinkage and collapse of the cotyledonary villi with subsequent fetal membrane separation.

Active management

Methods of active management include umbilical cord clamping, stimulation of uterine contraction and cord traction.

Umbilical cord clamping

Active management routinely involves clamping of the

umbilical cord In placental mammals, the umbilical cord (also called the navel string, birth cord or ''funiculus umbilicalis'') is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord is physiologi ...

, often within seconds or minutes of birth.

Uterine contraction

Uterine contraction Uterine contractions are muscle contractions of the uterine smooth muscle that occur during the menstrual cycle and labour. Uterine contractions occur throughout the menstrual cycle in the non-pregnant state and throughout gestation. Throughout ...

assists in delivering the placenta. Uterine contraction reduces the placental surface area, often forming a temporary hematoma at their former interface. Myometrial contractions can be induced with medication, usually oxytocin via intramuscular injection. The use of

ergometrine Ergometrine, also known as ergonovine and sold under the brand names Ergotrate, Ergostat, and Syntometrine among others, is a medication used to cause contractions of the uterus to treat heavy vaginal bleeding after childbirth. It can be used ei ...

, on the other hand, is associated with nausea or vomiting and hypertension.

Breastfeeding Breastfeeding, or nursing, is the process by which human breast milk is fed to a child. Breast milk may be from the breast, or may be expressed by hand or pumped and fed to the infant. The World Health Organization (WHO) recommends that br ...

soon after birth stimulates oxytocin which increases uterine tone, and through physical mechanisms uterine massage (the fundus) also causes uterine contractions.

Cord traction

Controlled cord traction (CCT) consists of pulling on the umbilical cord while applying counter pressure to help deliver the placenta. It may be uncomfortable for the mother. Its performance requires specific training. Premature cord traction can pull the placenta before it has naturally detached from the uterine wall, resulting in hemorrhage. Controlled cord traction requires the immediate clamping of the

. A

Cochrane review Cochrane (previously known as the Cochrane Collaboration) is a British international charitable organisation formed to organise medical research findings to facilitate evidence-based choices about health interventions involving health profes ...

came to the results that controlled cord traction does not clearly reduce severe postpartum hemorrhage (defined as blood loss >1000 mL) but overall resulted in a small reduction in postpartum hemorrhage (defined as blood loss >500 mL) and mean blood loss. It did reduce the risk of manual placenta removal. The review concluded that use of controlled cord traction should be recommended if the care provider has the skills to administer it safely.

Manual placenta removal

Manual placenta removal is the evacuation of the placenta from the uterus by hand. It is usually carried out under anesthesia or more rarely, under sedation and

analgesia Pain management is an aspect of medicine and health care involving relief of pain (pain relief, analgesia, pain control) in various dimensions, from acute and simple to chronic and challenging. Most physicians and other health professional ...

. A hand is inserted through the

vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...

into the uterine cavity and the placenta is detached from the uterine wall and then removed manually. A placenta that does not separate easily from the uterine surface indicates the presence of

placenta accreta Placenta accreta occurs when all or part of the placenta attaches abnormally to the '' myometrium'' (the muscular layer of the uterine wall). Three grades of abnormal placental attachment are defined according to the depth of attachment and invas ...

Efficacy of active management

Cochrane database Cochrane (previously known as the Cochrane Collaboration) is a British international charitable organisation formed to organise medical research findings to facilitate evidence-based choices about health interventions involving health profess ...

study suggests that blood loss and the risk of

postpartum bleeding Postpartum bleeding or postpartum hemorrhage (PPH) is often defined as the loss of more than 500 ml or 1,000 ml of blood following childbirth. Some have added the requirement that there also be signs or symptoms of low blood volume fo ...

will be reduced in women offered active management of the third stage of labour. 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.'' BMJ'' summary of the Cochrane group metanalysis, a
Postpartum Hemorrhage: prevention
by David Chelmow.

Retained placenta

retained placenta Retained placenta is a condition in which all or part of the placenta or membranes remain in the uterus during the third stage of labour. Retained placenta can be broadly divided into: * failed separation of the placenta from the uterine lining * p ...

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 ( or ), in medical procedures, is the use of a curette (French, meaning scoop Mosby's Medical, Nursing & Allied Health Dictionary, Fourth Edition, Mosby-Year Book 1994, p. 422) to remove tissue by scraping or scooping. Curettages are ...

is necessary to ensure that no remnants of the placenta remain (in conditions with very adherent placenta,

). 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 prostaglandin on the uterus after birth. This is known as

. However, it has been observed in zoology that chimpanzees 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 A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

, having arisen separately in evolution rather than being inherited from one distant common ancestor. Studies on pigs indicate that the duration of placenta expulsion increases significantly with increased duration of

farrowing Pig farming or pork farming or hog farming is the raising and breeding of domestic pigs as livestock, and is a branch of animal husbandry. Pigs are farmed principally for food (e.g. pork: bacon, ham, gammon) and skins. Pigs are amenable to ...

References

{{Authority control Obstetrics Midwifery