{{Short description|Ejection of the placenta from the uterus after childbirth}} {{Redirect|Afterbirth|the American Horror Story episode|Afterbirth (American Horror Story)|the video game|The Binding of Isaac: Afterbirth}} [[File:Placenta held.jpg|300px|thumb|Human placenta after expulsion]]'''Placental expulsion''' (also called '''afterbirth''') occurs when the [[placenta]] comes out of the [[birth canal]] after [[childbirth]]. The time between the expulsion of the baby and the expulsion of the placenta 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, with physiological management or passive management. The latter allows for the placenta to be expelled without medical assistance.
Although uncommon in some countries, the placenta is sometimes kept and consumed by the mother over the weeks following the birth. This practice is termed [[human placentophagy]] and can be harmful.<ref>{{Cite web |title=Eating the placenta: A good idea? |url=https://www.mayoclinic.org/healthy-lifestyle/labor-and-delivery/expert-answers/eating-the-placenta/faq-20380880 |access-date=2025-01-09 |website=Mayo Clinic |language=en}}</ref>
==Physiology==
=== Hormone induction of placental separation ===
As the fetal [[hypothalamus]] matures, the activation of the [[Hypothalamic–pituitary–adrenal axis|hypothalamic–pituitary–adrenal (HPA) axis]] initiates labor through two hormonal mechanisms. The end pathway of both mechanisms lead to contractions in the [[myometrium]], a mechanical cause of placental separation, which is due to the sheer force and contractile and involutive changes that occur within the [[uterus]], distorting the placentome.
==== Fetal adrenocorticotropic hormone (ACTH) ==== [[Adrenocorticotropic hormone|ACTH]] increases fetal [[cortisol]] which acts by two mechanisms:
* Increases [[Prostaglandin F2alpha|prostaglandin F<sub>2α</sub>]], which abolishes the progesterone block, lowers the [[oxytocin receptor]] threshold, and increases expression of [[relaxin]], stretching the pelvic ligaments * Increases expression of PTGS in the fetal [[trophoblast]]s
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., [[connexin]]s) * Placental shedding by physiological inflammation (note that 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 class I|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, [[Helper T Cells|T-helper 1 (Th1) cells]], and [[macrophage]]s 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 degradation 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 [[Placental cotyledon|cotyledonary]] villi with subsequent fetal membrane separation.<ref>Attupuram, N. M; Kumaresan, A; Narayanan, K; Kumar, H. Molecular Reproduction and Development Apr/2016, Volume 83, Issue 4, pp. 287 - 297</ref>
==Active management== Methods of active management include [[umbilical cord clamping]], stimulation of uterine contraction and cord traction.
===Umbilical cord clamping=== {{Main|Umbilical cord clamping}}
Active management routinely involves clamping of the [[umbilical cord]], often within seconds or minutes of birth.
===Uterine contraction=== [[Uterine contraction]] 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]], on the other hand, is associated with nausea or vomiting and hypertension.<ref name="Cochrane database"/>{{needs update|date=March 2025}}
[[Breastfeeding]] soon after birth stimulates oxytocin which increases uterine tone, and through physical mechanisms uterine massage (targeting the [[fundus (uterus)|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.<ref name="HofmeyrMshweshwe2015">{{cite journal|last1=Hofmeyr|first1=G Justus|last2=Mshweshwe|first2=Nolundi T|last3=Gülmezoglu|first3=A Metin|last4=Hofmeyr|first4=G Justus|title=Controlled cord traction for the third stage of labour|year=2015|doi=10.1002/14651858.CD008020.pub2|pmid=25631379|pmc=6464177|volume=1|journal=Cochrane Database Syst Rev|issue=5 |article-number=CD008020}}</ref> 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 [[umbilical cord]].
A [[Cochrane review]] 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.<ref name="HofmeyrMshweshwe2015"/>
===Manual placenta removal=== Manual placenta removal is the evacuation of the placenta from the uterus by hand.<ref name="pmid15207663">{{cite journal |vauthors=Dehbashi S, Honarvar M, Fardi FH |title=Manual removal or spontaneous placental delivery and postcesarean endometritis and bleeding |journal=Int J Gynaecol Obstet |volume=86 |issue=1 |pages=12–5 |date=July 2004 |pmid=15207663 |doi=10.1016/j.ijgo.2003.11.001 |s2cid=42420108 }}</ref> It is usually carried out under [[anesthesia]] or more rarely, under [[sedation]] and [[analgesia]]. A hand is inserted through the [[vagina]] and [[cervix]] 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]].
===Efficacy of active management=== A [[Cochrane database]] study<ref name="Cochrane database">{{cite journal|last1=Prendiville|first1=Walter JP|journal=Cochrane Database of Systematic Reviews|last2=Elbourne|first2=Diana|last3=McDonald|first3=Susan J|last4=Begley|first4=Cecily M|editor1-first=Cecily M|editor1-last=Begley|title=Active versus expectant management in the third stage of labour|year=2000|doi=10.1002/14651858.CD000007|pmid=10908457|issue=3|article-number=CD000007|s2cid=25741121 }} {{Retracted |doi=10.1002/14651858.cd000007.pub2|intentional=yes}}</ref>{{needs update|date=March 2025}} suggests that blood loss and the risk of [[postpartum bleeding]] will be reduced in women offered active management of the third stage of labour. A summary<ref name=Chelmow/> 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. It also reduced later morbidities including profuse 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.<ref name=Chelmow>''[[British Medical Journal|BMJ]]'' summary of the Cochrane group metanalysis, at [http://clinicalevidence.bmj.com/ceweb/conditions/pac/1410/1410_I1.jsp Postpartum Hemorrhage: prevention] {{Webarchive|url=https://web.archive.org/web/20081011220226/http://clinicalevidence.bmj.com/ceweb/conditions/pac/1410/1410_I1.jsp |date=2008-10-11 }} by David Chelmow.</ref>
==Retained placenta== A [[retained placenta]] is a placenta that does not 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. Very rarely, a [[curettage]] is necessary to ensure that no remnants of the placenta remain (in 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.<ref>{{Cite journal |last1=Kirz |first1=D. S. |last2=Haag |first2=M. K. |date=February 1989 |title=Management of the third stage of labor in pregnancies terminated by prostaglandin E2 |journal=American Journal of Obstetrics and Gynecology |volume=160 |issue=2 |pages=412–414 |doi=10.1016/0002-9378(89)90460-2 |issn=0002-9378 |pmid=2916627}}</ref>
==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.{{Citation needed|date=November 2024}} This is known as [[placentophagy]]. 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 likely [[Polyphyly|polyphyletic]], having arisen separately in evolution rather than being inherited from one distant common ancestor.<ref>{{Cite journal |last1=Wildman |first1=Derek E. |last2=Chen |first2=Caoyi |last3=Erez |first3=Offer |last4=Grossman |first4=Lawrence I. |last5=Goodman |first5=Morris |last6=Romero |first6=Roberto |date=2006-02-28 |title=Evolution of the mammalian placenta revealed by phylogenetic analysis |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=103 |issue=9 |pages=3203–3208 |doi=10.1073/pnas.0511344103 |doi-access=free |issn=0027-8424 |pmc=1413940 |pmid=16492730}}</ref>
Studies on pigs indicate that the duration of placenta expulsion increases significantly with increased duration of [[farrowing]].<ref>{{Cite journal | doi = 10.1016/j.theriogenology.2003.10.008 | last1 = Rens | first1 = B. | last2 = Van Der Lende | first2 = T. | title = Parturition in gilts: duration of farrowing, birth intervals and placenta expulsion in relation to maternal, piglet and placental traits | journal = Theriogenology | volume = 62 | issue = 1–2 | pages = 331–352 | year = 2004 | pmid = 15159125}}</ref>
==References== {{Reflist}}
{{Pregnancy}} {{Authority control}}
[[Category:Placenta]] [[Category:Obstetrics]] [[Category:Midwifery]]