MoonDragon's Pregnancy Information
PLACENTA ANATOMY & PHYSIOLOGY
(Includes Placenta Delivery Instructions)
For "Informational Use Only".
For more detailed information, contact your health care provider
about options that may be available for your specific situation.
As a midwife, I think the placenta is a really cool little "organ". It supports life throughout the gestational period of a developing fetus, supplying oxygen, hormones, fluids, and food while eliminating metabolic wastes. It is the only disposable organ of the mammalian body. It is also the only "meat" that is formed from life and can be consumed (eaten) by the female mammal without causing death of another organism. It is truly a fascinating little thing.
The Placenta [plusen´tu], commonly called the afterbirth, is an organ that develops in the uterus during pregnancy. It is a unique characteristic of the higher (or placental) mammals. In humans it is a thick mass, about 7 inches (18 cm) in diameter, liberally supplied with blood vessels. It usually weighs about 1 to 2 pounds (about 1/6 of the weight of the baby). The placenta is attached to the uterus, and the fetus is connected to the placenta by the umbilical cord. The placenta draws nourishment and oxygen, which it supplies to the fetus, from the maternal circulation. In turn, the placenta receives the wastes of fetal metabolism and discharges them into the maternal circulation for disposal. It also acts as an endocrine gland, producing estrogen, progesterone, and gonadotropin. Shortly after delivery of the fetus the placenta is forced out by contractions of the uterus. Severe hemorrhage may occur if the placenta does not emerge in its entirety or if the uterus fails to contract properly.
DEVELOPMENT OF THE FETAL MEMBRANES & PLACENTA
THE ALLANTOIS: The allantois arises as a tubular diverticulum of the posterior part of the yolk-sac; when the hind-gut is developed the allantois is carried backward with it and then opens into the cloaca or terminal part of the hind-gut: it grows out into the body-stalk, a mass of mesoderm which lies below and around the tail end of the embryo. The diverticulum is lined by entoderm and covered by mesoderm, and in the latter are carried the allantoic or umbilical vessels.
In reptiles, birds, and many mammals the allantois becomes expanded into a vesicle which projects into the extra-embryonic celom. If its further development be traced in the bird, it is seen to project to the right side of the embryo, and, gradually expanding, it spreads over its dorsal surface as a flattened sac between the amnion and the serosa, and extending in all directions, ultimately surrounds the yolk. Its outer wall becomes applied to and fuses with the serosa, which lies immediately inside the shell membrane. Blood is carried to the allantoic sac by the two allantoic or umbilical arteries, which are continuous with the primitive aorta, and after circulating through the allantoic capillaries, is returned to the primitive heart by the two umbilical veins. In this way the allantoic circulation, which is of the utmost importance in connection with the respiration and nutrition of the chick, is established. Oxygen is taken from, and carbonic acid is given up to the atmosphere through the egg-shell, while nutritive materials are at the same time absorbed by the blood from the yolk.
Diagram showing earliest observed stage of human ovum. Diagram illustrating early formation of allantois and differentiation of body-stalk. Diagram showing later stage of allantoic development with commencing constriction of the yolk-sac. Diagram showing the expansion of amnion and delimitation of the umbilicus.
In humans and other primates the nature of the allantois is entirely different from that just described. Here it exists merely as a narrow, tubular diverticulum of the hind-gut, and never assumes the form of a vesicle outside the embryo. With the formation of the amnion the embryo is, in most animals, entirely separated from the chorion, and is only again united to it when the allantoic mesoderm spreads over and becomes applied to its inner surface. The human embryo is never wholly separated from the chorion, its tail end being from the first connected with the chorion by means of a thick band of mesoderm, named the body-stalk (Bauchstiel); into this stalk the tube of the allantois extends.
THE AMNION: The amnion is a membranous sac which surrounds and protects the embryo. It is developed in reptiles, birds, and mammals, which are hence called "Amniota;" but not in amphibia and fishes, which are consequently termed "Anamnia."
In the human embryo the earliest stages of the formation of the amnion have not been observed; in the youngest embryo which has been studied the amnion was already present as a closed sac and appears in the inner cell-mass as a cavity. This cavity is roofed in by a single stratum of flattened, ectodermal cells, the amniotic ectoderm, and its floor consists of the prismatic ectoderm of the embryonic disk - the continuity between the roof and floor being established at the margin of the embryonic disk. Outside the amniotic ectoderm is a thin layer of mesoderm, which is continuous with that of the somatopleure and is connected by the body-stalk with the mesodermal lining of the chorion.
Diagram illustrating a later stage in the development of the umbilical cord.
When first formed the amnion is in contact with the body of the embryo, but about the fourth or fifth week fluid (liquor amnii) begins to accumulate within it. This fluid increases in quantity and causes the amnion to expand and ultimately to adhere to the inner surface of the chorion, so that the extra-embryonic part of the celom is obliterated. The liquor amnii increases in quantity up to the sixth or seventh month of pregnancy, after which it diminishes somewhat; at the end of pregnancy it amounts to about 1 liter. It allows of the free movements of the fetus during the later stages of pregnancy, and also protects it by diminishing the risk of injury from without. It contains less than 2 per cent. of solids, consisting of urea and other extractives, inorganic salts, a small amount of protein, and frequently a trace of sugar. That some of the liquor amnii is swallowed by the fetus is proved by the fact that epidermal debris and hairs have been found among the contents of the fetal alimentary canal.
In reptiles, birds, and many mammals the amnion is developed in the following manner: At the point of constriction where the primitive digestive tube of the embryo joins the yolk-sac a reflection or folding upward of the somatopleure takes place. This, the amniotic fold, first makes its appearance at the cephalic extremity, and subsequently at the caudal end and sides of the embryo, and gradually rising more and more, its different parts meet and fuse over the dorsal aspect of the embryo, and enclose a cavity, the amniotic cavity. After the fusion of the edges of the amniotic fold, the two layers of the fold become completely separated, the inner forming the amnion, the outer the false amnion or serosa. The space between the amnion and the serosa constitutes the extra-embryonic celom, and for a time communicates with the embryonic celom.
Diagram of a transverse section, showing the mode of formation of the amnion in the chick. The amniotic folds have nearly united in the middle line. (From Quain's Anatomy.) Ectoderm, blue; mesoderm, red; entoderm and notochord, black. Fetus of about eight weeks, enclosed in the amnion. Magnified a little over two diameters. (Drawn from stereoscopic photographs lent by Professor A. Thomson, Oxford.)
THE UMBILICAL CORD & BODY-STALK: The umbilical cord attaches the fetus to the placenta; its length at full time, as a rule, is about equal to the length of the fetus, i.e., about 50 cm., but it may be greatly diminished or increased. The rudiment of the umbilical cord is represented by the tissue which connects the rapidly growing embryo with the extra-embryonic area of the ovum. Included in this tissue are the body-stalk and the vitelline duct - the former containing the allantoic diverticulum and the umbilical vessels, the latter forming the communication between the digestive tube and the yolk-sac. The body-stalk is the posterior segment of the embryonic area, and is attached to the chorion. It consists of a plate of mesoderm covered by thickened ectoderm on which a trace of the neural groove can be seen, indicating its continuity with the embryo. Running through its mesoderm are the two umbilical arteries and the two umbilical veins, together with the canal of the allantois - the last being lined by entoderm. Its dorsal surface is covered by the amnion, while its ventral surface is bounded by the extra-embryonic celom, and is in contact with the vitelline duct and yolk-sac. With the rapid elongation of the embryo and the formation of the tail fold, the body stalk comes to lie on the ventral surface of the embryo, where its mesoderm blends with that of the yolk-sac and the vitelline duct. The lateral leaves of somatopleure then grow round on each side, and, meeting on the ventral aspect of the allantois, enclose the vitelline duct and vessels, together with a part of the extra-embryonic celom; the latter is ultimately obliterated. The cord is covered by a layer of ectoderm which is continuous with that of the amnion, and its various constituents are enveloped by embryonic gelatinous tissue, jelly of Wharton. The vitelline vessels and duct, together with the right umbilical vein, undergo atrophy and disappear; and thus the cord, at birth, contains a pair of umbilical arteries and one (the left) umbilical vein.
Model of human embryo 1.3 mm. long.
IMPLANTATION or IMBEDDING OR THE OVUM: Fertilization of the ovum occurs in the lateral or ampullary end of the uterine tube and is immediately followed by segmentation. On reaching the cavity of the uterus the segmented ovum adheres like a parasite to the uterine mucous membrane, destroys the epithelium over the area of contact, and excavates for itself a cavity in the mucous membrane in which it becomes imbedded. In the ovum described by Bryce and Teacher 7 the point of entrance was visible as a small gap closed by a mass of fibrin and leukocytes; in the ovum described by Peters, the opening was covered by a mushroom-shaped mass of fibrin and blood-clot, the narrow stalk of which plugged the aperture in the mucous membrane. Soon, however, all trace of the opening is lost and the ovum is then completely surrounded by the uterine mucous membrane.
The structure actively concerned in the process of excavation is the trophoblast of the ovum, which possesses the power of dissolving and absorbing the uterine tissues. The trophoblast proliferates rapidly and forms a network of branching processes which cover the entire ovum and invade and destroy the maternal tissues and open into the maternal blood vessels, with the result that the spaces in the trophoblastic network are filled with maternal blood; these spaces communicate freely with one another and become greatly distended and form the intervillous space.
Section through ovum imbedded in the uterine decidua. Semi-diagrammatic. (After Peters.) am. Amniotic cavity. b.c. Blood-clot. b.s. Body-stalk. etc. Embryonic ectoderm. ent. Entoderm. mes. Mesoderm. m.v. Maternal vessels. tr. Trophoblast. u.e. Uterine epithelium. u.g. Uterine glands. y.s. Yolk-sac.
THE DECIDUA: Before the fertilized ovum reaches the uterus, the mucous membrane of the body of the uterus undergoes important changes and is then known as the decidua. The thickness and vascularity of the mucous membrane are greatly increased; its glands are elongated and open on its free surface by funnel-shaped orifices, while their deeper portions are tortuous and dilated into irregular spaces. The interglandular tissue is also increased in quantity, and is crowded with large round, oval, or polygonal cells, termed decidual cells. These changes are well advanced by the second month of pregnancy, when the mucous membrane consists of the following strata:
1. Stratum compactum, next the free surface; in this the uterine glands are only slightly expanded, and are lined by columnar cells.
2. Stratum spongiosum, in which the gland tubes are greatly dilated and very tortuous, and are ultimately separated from one another by only a small amount of interglandular tissue, while their lining cells are flattened or cubical.
3. A thin unaltered or boundary layer, next the uterine muscular fibers, containing the deepest parts of the uterine glands, which are not dilated, and are lined with columnar epithelium; it is from this epithelium that the epithelial lining of the uterus is regenerated after pregnancy.
Distinctive names are applied to different portions of the decidua. The part which covers in the ovum is named the decidua capsularis; the portion which intervenes between the ovum and the uterine wall is named the decidua basalis or decidua placentalis; it is here that the placenta is subsequently developed. The part of the decidua which lines the remainder of the body of the uterus is known as the decidua vera or decidua parietalis.
Coincidently with the growth of the embryo, the decidua capsularis is thinned and extended and the space between it and the decidua vera is gradually obliterated, so that by the third month of pregnancy the two are in contact. By the fifth month of pregnancy the decidua capsularis has practically disappeared, while during the succeeding months the decidua vera also undergoes atrophy, owing to the increased pressure. The glands of the stratum compactum are obliterated, and their epithelium is lost. In the stratum spongiosum the glands are compressed and appear as slit-like fissures, while their epithelium undergoes degeneration. In the unaltered or boundary layer, however, the glandular epithelium retains a columnar or cubical form.
Diagrammatic sections of the uterine mucous membrane:
A. The non-pregnant uterus.
B. The pregnant uterus, showing the thickened mucous membrane and the altered condition of the uterine glands.
(Kundrat and Engelmann.)
Sectional plan of the gravid uterus in the third and fourth month. (Modified from Wagner.)
THE CHORION: The chorion consists of two layers: an outer formed by the primitive ectoderm or trophoblast, and an inner by the somatic mesoderm; with this latter the amnion is in contact. The trophoblast is made up of an internal layer of cubical or prismatic cells, the cytotrophoblast or layer of Langhans, and an external layer of richly nucleated protoplasm devoid of cell boundaries, the syncytiotrophoblast. It undergoes rapid proliferation and forms numerous processes, the chorionic villi, which invade and destroy the uterine decidua and at the same time absorb from it nutritive materials for the growth of the embryo. The chorionic villi are at first small and non-vascular, and consist of trophoblast only, but they increase in size and ramify, while the mesoderm, carrying branches of the umbilical vessels, grows into them, and in this way they are vascularized. Blood is carried to the villi by the branches of the umbilical arteries, and after circulating through the capillaries of the villi, is returned to the embryo by the umbilical veins. Until about the end of the second month of pregnancy the villi cover the entire chorion, and are almost uniform in size, but after this they develop unequally. The greater part of the chorion is in contact with the decidua capsularis, and over this portion the villi, with their contained vessels, undergo atrophy, so that by the fourth month scarcely a trace of them is left, and hence this part of the chorion becomes smooth, and is named the chorion læve; as it takes no share in the formation of the placenta, it is also named the non-placental part of the chorion. On the other hand, the villi on that part of the chorion which is in contact with the decidua placentalis increase greatly in size and complexity, and hence this part is named the chorion frondosum.
Transverse section of a chorionic villus. Primary chorionic villi. Diagrammatic.
(Modified from Bryce.)
THE PLACENTA: The placenta connects the fetus to the uterine wall, and is the organ by means of which the nutritive, respiratory, and excretory functions of the fetus are carried on. It is composed of fetal and maternal portions.
Secondary chorionic villi. Diagrammatic. (Modified from Bryce.)
FETAL PORTION: The fetal portion of the placenta consists of the villi of the chorion frondosum; these branch repeatedly, and increase enormously in size. These greatly ramified villi are suspended in the intervillous space, and are bathed in maternal blood, which is conveyed to the space by the uterine arteries and carried away by the uterine veins. A branch of an umbilical artery enters each villus and ends in a capillary plexus from which the blood is drained by a tributary of the umbilical vein. The vessels of the villus are surrounded by a thin layer of mesoderm consisting of gelatinous connective tissue, which is covered by two strata of ectodermal cells derived from the trophoblast: the deeper stratum, next the mesodermic tissue, represents the cytotrophoblast or layer of Langhans; the superficial, in contact with the maternal blood, the syncytiotrophoblast. After the fifth month the two strata of cells are replaced by a single layer of somewhat flattened cells.
MATERNAL PORTION: The maternal portion of the placenta is formed by the decidua placentalis containing the intervillous space. As already explained, this space is produced by the enlargement and intercommunication of the spaces in the trophoblastic network. The changes involve the disappearance of the greater portion of the stratum compactum, but the deeper part of this layer persists and is condensed to form what is known as the basal plate. Between this plate and the uterine muscular fibers are the stratum spongiosum and the boundary layer; through these and the basal plate the uterine arteries and veins pass to and from the intervillous space. The endothelial lining of the uterine vessels ceases at the point where they terminate in the intervillous space which is lined by the syncytiotrophoblast. Portions of the stratum compactum persist and are condensed to form a series of septa, which extend from the basal plate through the thickness of the placenta and subdivide it into the lobules or cotyledons seen on the uterine surface of the detached placenta.
Fetus in utero, between fifth and sixth months.
The fetal and maternal blood currents traverse the placenta, the former passing through the blood vessels of the placental villi and the latter through the intervillous space. The two currents do not intermingle, being separated from each other by the delicate walls of the villi. Nevertheless, the fetal blood is able to absorb, through the walls of the villi, oxygen and nutritive materials from the maternal blood, and give up to the latter its waste products. The blood, so purified, is carried back to the fetus by the umbilical vein. It will thus be seen that the placenta not only establishes a mechanical connection between the mother and the fetus, but subserves for the latter the purposes of nutrition, respiration, and excretion. In favor of the view that the placenta possesses certain selective powers may be mentioned the fact that glucose is more plentiful in the maternal than in the fetal blood. It is interesting to note also that the proportion of iron, and of lime and potash, in the fetus is increased during the last months of pregnancy. Further, there is evidence that the maternal leukocytes may migrate into the fetal blood, since leukocytes are much more numerous in the blood of the umbilical vein than in that of the umbilical arteries.
The placenta is usually attached near the fundus uteri, and more frequently on the posterior than on the anterior wall of the uterus. It may, however, occupy a lower position and, in rare cases, its site is close to the orificium internum uteri, which it may occlude, thus giving rise to the condition known as placenta previa.
Scheme of placental circulation.
SEPARATION OF THE PLACENTA: After the child is born, the placenta and membranes are expelled from the uterus as the after-birth. The separation of the placenta from the uterine wall takes place through the stratum spongiosum, and necessarily causes rupture of the uterine vessels. The orifices of the torn vessels are, however, closed by the firm contraction of the uterine muscular fibers, and thus postpartum hemorrhage is controlled. The epithelial lining of the uterus is regenerated by the proliferation and extension of the epithelium which lines the persistent portions of the uterine glands in the unaltered layer of the decidua.
The expelled placenta appears as a discoid mass which weighs about 450 grams and has a diameter of from 15 to 20 cm. Its average thickness is about 3 cm., but this diminishes rapidly toward the circumference of the disk, which is continuous with the membranes. Its uterine surface is divided by a series of fissures into lobules or cotyledons, the fissures containing the remains of the septa which extended between the maternal and fetal portions. Most of these septa end in irregular or pointed processes; others, especially those near the edge of the placenta, pass through its thickness and are attached to the chorion. In the early months these septa convey branches of the uterine arteries which open into the intervillous space on the surfaces of the septa. The fetal surface of the placenta is smooth, being closely invested by the amnion. Seen through the latter, the chorion presents a mottled appearance, consisting of gray, purple, or yellowish areas. The umbilical cord is usually attached near the center of the placenta, but may be inserted anywhere between the center and the margin; in some cases it is inserted into the membranes, i. e., the velamentous insertion. From the attachment of the cord the larger branches of the umbilical vessels radiate under the amnion, the veins being deeper and larger than the arteries. The remains of the vitelline duct and yolk-sac may be sometimes observed beneath the amnion, close to the cord, the former as an attenuated thread, the latter as a minute sac.
On section, the placenta presents a soft, spongy appearance, caused by the greatly branched villi; surrounding them is a varying amount of maternal blood giving the dark red color to the placenta. Many of the larger villi extend from the chorionic to the decidual surface, while others are attached to the septa which separate the cotyledons; but the great majority of the villi hang free in the intervillous space.
Embryo between eighteen and twenty-one days. (His.)
Head end of human embryo, about the end of the fourth week.
(From model by Peter.)
BIRTH OF A NORMAL PLACENTA DURING CHILDBIRTH
A Midwife's Tutorial
1. INTRODUCTION TO MANAGEMENT OF THE NORMAL THIRD STAGE
DEFINITION: The third stage is the time from the complete delivery of the baby to the complete delivery of the seccundines (placenta, cord and membranes).
OVERVIEW: The management of the normal third stage is undoubtedly the period of greatest importance to the health and well being of the mother during childbirth. Facilitating and supporting the normal mechanisms of third stage labor will result in a benign course of events.
Unfortunately, it is a time when the birth attendant is most tempted to interfere unnecessarily. Fatigue, a desire to complete the birth and go on to other activities, and/or a mistaken belief that blood loss will be reduced by active intervention may all result in an urge to hurry the process.
The midwife, whose model of practice is one of support and facilitation of normal processes, only intervening when medically indicated, will resist the urge to complete the normal birth of the placenta before natural processes occur.
The benefit to be obtained will be:
2. NORMAL ANATOMY & PHYSIOLOGY OF THE THIRD STAGE OF LABOR
- A more comfortable mother.
- A continued peaceful completion of the birth experience.
- An enhanced appreciation of the marvelous mechanisms at work to smoothly empty the uterus of its final contents.
- And most importantly, avoidance of occurrences which may lead to increased trauma, bleeding and/or infection.
Process of placental growth and uterine wall changes during pregnancy:
Anatomy of the uterine/placental compartment at the time of birth:
- The placenta grows with the placental site during pregnancy.
- During pregnancy and early labor the area of the placental site probably changes little, even during uterine contractions.
- The semi-rigid, non-contractile placenta cannot alter its surface area.
The process of placental separation during and after birth:
- The cotyledons of the maternal surface of the placenta extend into the decidua basalis, which forms a natural cleavage plane between the placenta and the uterine wall.
- There are interlacing uterine muscle bundles, consisting of tiny myofibrils, around the branches of the uterine arteries that run through the wall of the uterus to the placental area.
- The placental site is usually located on either the anterior or the posterior uterine wall.
- The amniotic membranes are adhered to the inner wall of the uterus except where the placenta is located.
- The surface area of the uterine cavity gradually increases during pregnancy and rapidly decreases during the second stage of labor.
- Separation involves a slow, progressive detachment from the uterine wall brought about by the physical changes which occur during and after the actual birth of the baby.
- The placenta is separated from the decidual attachment by the action of the uterine muscle.
- As the baby gradually leaves the uterus, the cavity of the uterus must become progressively smaller to permit the uterine wall to remain closely approximated to the baby. This maintains the expulsive force of the muscular contractions on the body of the baby.
- The mechanism for achieving this close approximation is through a slight shortening or retraction of the individual muscle fibers during each contraction. Slow delivery of the shoulders and body of the infant will permit the muscle fibers to retract and adjust to the reduction in size of the cavity, thereby promoting more efficient contractions.
- As the surface area of the interior of the uterus slightly reduces the diameters of the placental site, the placenta becomes thicker and decreases slightly in diameter.
- Since the placenta has a limited ability to alter its surface area, it must separate if the area to which it is attached is reduced considerably in size.
- The separation, which occurs in the outer portion of the spongy layer of the decidua basalis, begins during the later second stage of labor and is usually completed as the uterus contracts during the final expulsion of the baby.
- The effectiveness of this process depends on the extent to which the placental site is reduced. If the contractions are firm and forceful, the placenta may be expelled almost immediately after the baby is born. However, if they are less effective, complete placental separation may be delayed.
- The blood sinuses at the placental site, which have been opened by partial or complete separation of the placenta, are the source of bleeding during and after the third stage of normal labor. This bleeding is controlled initially by firm contraction of the interlacing uterine muscle bundles around the branches of the uterine arteries.
- The vessels are compressed and kinked.
- Bleeding from the open ends is slight.
- If the uterine muscle is relaxed, the bleeding will be brisk and continuous.
The process of expulsion of the placenta after separation - Expulsion of the placenta is a function of abdominal, uterine, and gravitational forces and cord traction by the attendant.
Immediately following the birth of the placenta:
- After separation, blood accumulates behind the placenta, and the uterus rises in the abdomen. A firm uterine contraction now begins, and the uterus changes from a flattened, soft, discoid organ to one that is firm and globular. This process can take from several minutes to much longer, depending on the strength of the uterine contractions and the location of the placenta within the uterus. A lower implantation will mean less firm contractions in the lower uterine segment and a longer time for separation and expulsion.
- During a uterine contraction, the flattened uterine body of the uterus becomes globular as the placenta is forced downward into the lower uterine segment.
- As the placenta leaves the upper part of the uterus, the uterus can be felt through the abdominal wall as a hard, globular mass.
Birth of the placenta by the Schultz Mechanism:
- The fetal surface of the placenta slips through the opening in the fetal membranes and appears at the introitus.
- The membranes then peel off the surface of the uterine cavity, uniformly and intact.
- The liquid blood and retroplacental clots, if any, are contained within the folded placenta and are not evident until the placenta is delivered and examined.
Birth of the placenta by the Duncan Mechanism:
- One edge of the placenta first slips through the cervix and into the vagina. The remainder of the placenta follows, and the fetal membranes are peeled from the uterus as traction is made on the edge of the placenta which follows.
- The liquid blood and retroplacental clots escape from the uterus as the maternal surface of the placenta is delivered.
- The Duncan Mechanism is more frequently followed by retained fragments of the fetal membranes.
- Uterine contractions continue, with the muscle fibers creating living ligatures to provide hemostasis.
The contracted body of the uterus forms a hard globular mass, the apex of which is about midway between the umbilicus and symphysis. This solid mass of tissue contains a flattened cavity with anterior and posterior walls in close apposition, each measuring 4-5 cm in thickness. Because of its compression by the contracted myometrium, the uterus appears anemic, as contrasted with the purplish pregnant uterus. A portion of the decidua, which remains, has an irregular jagged appearance, and marked infiltration with blood, especially at the placental site.Extrusion of the placental site takes up to six weeks.
Williams describes the process as follows: Involution.... "is not effected by absorption in situ, but rather by a process of exfoliation which is in great part brought about by the undermining of the placental site by the growth of endometrial tissue.... Such a process of exfoliation should be regarded as very conservative, and as a wise provision on the part of nature: otherwise great difficulty might be experienced in getting rid of the obliterated arteries and organized thrombi which, if they remained in situ, would soon convert a considerable part of the mucosa into a mass of scar tissue with the result that after a few pregnancies it would no longer be possible for it to go through its usual cycle of changes, and the reproductive career would come to an untimely end."
- After delivery, the placental site is an irregular, nodular, elevated area about the size of the palm of the hand.
- By the end of the second week the placental site measures 3 to 4 cms in diameter.
Williams, J. W. Regeneration of the uterine mucosa after delivery with especial reference to the placental site. Amer J Obstet Gynec 22:664, 1931.
MIDWIFE'S TUTORIAL: BIRTH OF THE PLACENTA
Labor Initiation: Getting It Going Introduction to Stages of Labor Stage 1 of Labor & Birth: Contractions, Dilation & Effacement of the Cervix Stage 2 of Labor & Birth: Pushing The Baby Out Stage 3 of Labor & Birth: Placental Delivery Stage 4 of Labor & Birth: Immediately Postpartum
STAGE 3 LABOR
After a brief time (usually 15 to 45 minutes after the birth of the baby), mild contractions begin again. As the uterus contracts, the placenta (afterbirth) separates from the uterine wall and is expelled during this phase. Initiating breast-feeding at birth releases the hormone oxytocin, which stimulates the contractions of the uterus.
When giving birth at home, your midwife will usually try to get your baby on your breast as quickly as possible to stimulate uterine contractions and aid in the expelling of the uterus and clamping down of the uterine muscle afterward to prevent excessive bleeding (hemorrhage). A safe delivery of the placenta with minimal blood loss is the goal of the midwife. The delivery of the placenta should only be attempted when the placenta if fully separated to avoid uterine inversion (uterus turning inside out) or pulling off a section of the placenta from the wall of the uterus leaving the remainder attached, thus creating an open bleeding area in the uterine wall.
Expelling the placenta.
Uterine involution (the gradual return to normal size) begins. Placental expulsion may be accompanied by a sudden gush of blood. If the uterus does not contract and remain firm, hemorrhaging may occur.
DELIVERY OF THE PLACENTA
Uterus and placenta before birth, fetal front view.
Uterus and placenta after birth.
Without the baby in the uterus, it begins to contract down and reduce in size, forcing the placenta to release and sealing up blood vessels located behind the placenta, pushing the placenta out through the cervix and vagina.
After birth of baby, the cord stops pulsating and is cut, severing the baby from the mother. The midwife follows the cord and grasps it at the vaginal opening, taking up any cord slack, pulling it straight out the vaginal opening.
A large ring forceps is clamped onto the cord at the entrance to the vagina and let it hang down by its own weight.
Placenta Delivery: Placental Separation, Uterine Configuration. Checking for placental separation and release along with uterine tone and contraction by placing a hand on the uterus. Do not massage the uterus. Allow it to contract on its own. When the uterus contracts, it will form a hard globular ball which rises slightly under your hand. Tell the mother to let you know when she begins to have contractions again.
Placenta Delivery: Noting whether there is a gush of blood and/or lengthening of the cord may not always be readily apparent. Keep track of time since the birth to when separation occurs. At home, this may take longer (usually 15 to 45 minutes) than the hospital (5 to 20 minutes) because many homebirth midwives do not give medications to stimulate contractions like they do in a hospital setting. Checking placental separation and release from the uterus by placing a hand on the uterus and using the other hand for cord traction. Uterine firmness is noted.
Cord traction is applied, using the ring forceps to obtain a firm hold (the cord is very slippery), taunt traction is done, pulling gently but firmly away from the vagina. The mother should be having contractions at this point. There is usually a little gush of blood as the placenta begins to pull away from the uterine wall. Placenta separation may be apparent by the increasing cord length between the forceps and the vaginal opening.
Placenta Delivery: Controlled cord traction. Have the mother begin pushing with her contractions. If there is a gush of blood and lengthening of the cord, have the mother push whether or not there is a contraction.
Placenta Delivery: Using one hand to apply suprapubic pressure against the fundus of the uterus with your cupped hand, and your thumb placed just above the pubic bone to keep the uterus from entering the pelvis and causing spurious cord lengthening or other false evidence of separation, or even inverting the uterus. Provide some steady cord traction to not whether there is a sense of "give" as the placenta moves into the vagina and the cord lengthens, or conversely, does not progress, in which case cease your maneuvers and wait. If you are uncertain whether the placenta has actually separated, you may follow the cord with your hand in the vagina, up to the cervix, to determine if the placenta is trapped in the cervical os, or whether the cord disappears into the uterus.
NOTE: In the absence of heavy bleeding, there is no hurry to deliver the placenta. It is normal and safe, if there is no bleeding, to wait up to an hour, checking for separation periodically. The placenta has been known to stay attached to the uterine wall for days after a delivery. If this occurs because there is acreta, this is the safe state until the problem can be evaluated more completely.
Conversely, if you do not make an accurate diagnosis of separation and separation has indeed occurred, then the uterus may be silently filling with blood. This is another reason for keeping your abdominal hand over the uterus at all times until the delivery of the placenta is imminent at the introitus.
Placenta Delivery:Use maternal efforts to deliver the placenta, assisted by the following maneuvers, as needed, when you believe the separation has occurred. Maintain your abdominal hand over the uterus, using your flattened fingers just above the pubic bone to aid the placenta as it exits the cervical os into the vagina. Instead of pressure with flattened fingers, the Brandt Andrews maneuver may also be used, but this is more uncomfortable for the mother. Place your fingers around the ring forceps at the point where the cord is attached, and apply steady cord traction with a downward motion. The Upward Placental Lift: then upward along the curve of Carus as the placenta traverses the vagina to the introitus. When the placenta is visible at the introitus, lift it partially through with the hand holding the ring forceps.
Placenta Delivery: Remove your other hand from the abdomen and let the placenta fall into your hands. At this point, drop the cord and ring forceps. Encompass the placenta using both hands to support it during delivery, making sure the membranes do not tear.
Placenta Delivery: Using an Up-Down-Rotation method to bring it through the os.
Placenta Delivery: Once the placenta is delivered, continue to rotate it and the membranes to form a thicker cord of membranes help the membranes release intact without tearing or redding.
Placenta Delivery: Grasping the membranes with the ring forceps to help in delivery and to aid in making a thicker cord of membranes.
Placenta Delivery of the Membranes: Rotating the ring forceps to "tease" the membranes loose from the uterine lining without shredding them by a slight up and down movement. NOTE: Slow controlled delivery is necessary to avoid tearing of the cord or membranes.
Placenta Delivery Cleanup: Once the placenta is out, massage the belly once or twice above the uterus to get the uterus to contract and form a grapefruit size firm ball under your hand. Wipe out the blood from the introitus (vaginal opening) after the delivery of the placenta to determine if you have additional bleeding.
while keeping an eye on the vaginal opening for bleeding, conduct a complete inspection of the fetal and maternal surfaces of the placenta. This quick examination is conducted to be sure the entire placenta is out. Examinations of both the maternal and the fetal side of the placenta are done and note any abnormalities. This should take no more than 15 seconds and is a critical step before using medications or other remedies to manage a heavy bleed or hemorrhage, if there is a problem.
Examining the placenta and the placental membranes to make sure it is intact (no missing parts).
Examining the placenta and membranes (formerly the bag of waters or amniotic bag in which housed the baby before birth). Ideally there should be only one hole in the membranes (where the baby came through at birth).
Placenta, Fetal Side
Placenta, Maternal Side
Placenta Exam: Start with the fetal surface since that is the most common presentation of the placenta at birth (shiny schultz). Fetal Surface - note general size and shape and look for any variations or for any abnormalities, such as a circumvallate placenta (an opaque ring on the fetal surface formed by a doubling back of the chorion and amnion membranes), extra placental lobes, vessels running off the edge of the placenta (which could mean that a placental lobe may still be in the uterus).
Placenta Exam: Note the cord insertion location. A normal placenta should have the cord firmly attached into the center or near the center of the placenta (concentric). Other variations include eccentric (away from the center of the placenta), or more rarely a Battledore placenta (the cord at the edge of the placenta). Occasionally seen is a velamentous insertion of the cord in which the umbilical vessels run through the membranes from the cord to the placenta, without the protection of the gelatinous portion of the cord, which ends several centimeters above where the vessels insert into the placenta.
Placenta Exam of the Membranes: Turning the placenta over to the maternal surface, pull the membranes up gently to identify the location of the hole which resulted from the rupture of the membranes. Checking for tears in the membranes with a hole near the center of the membranes indicates a placenta attached to the upper portion of the uterus. A hole near the edge of a placenta indicates a low lying placenta (one attached in the lower uterine segment closer to the cervical os. Ideally there should only be one tear - the one the baby came out of.
Placenta Exam: Checking membrane for both layers - The Amnion and the Chorion.
Placenta Exam: Placental Cord Vessels - There should be three in a normal umbilical cord (2 arteries and 1 vein).
Placenta Exam: Maternal Surface Inspection. After noting whether or not there were tears in the membranes or blood vessels passing through them, pull the membranes completely back to expose the maternal surface of the placenta. Look for and note the cotyledons which make up a normally thick, red surface and ensure that there is not any missing pieces or sections that may still be in the uterus. Note any blood clots, calcified infarctions (white, thickened areas), or a pale overall color. These signs indicate an aging placenta, or one that has not had a healthy maternal/fetal transfer unit. Run your finger around the edge areas of the placenta to determine whether there are any vessels or succinturiate lobes in the membranes. NOTE: any retained uterine fragments may cause severe bleeding problems (hemorrhage) since the uterus is not able to effectively contract down to close off open uterine vessels found in the former placental site. This can be life threatening, which is why it is important to do a proper placental examination. The mother may be given oxytocin, methergine, or other medications if needed. These medications are not usually required in a normal third stage of labor with minimal bleeding.
Placenta Exam: Maternal Side Inspection of Cotyledons, looking for missing pieces, broken vessels and missing extra placental lobes.
Placenta Exam: Checking for meconium, maternal side of the placenta. Meconium is the blackish-greenish tar-like feces found in the newborn. Sometimes during labor, the baby becomes stressed and may lose oxygen. When this happens, it causes the anal sphincter to relax and the baby releases the meconium into the amniotic fluid, staining the fluid, the placenta and the baby. If the baby happens to breathe this meconium into the lungs at the time of birth, it can make the baby very sick and cause severe breathing difficulties and neonatal lung infections.
Placenta Exam: Meconium staining on placental lobes, fetal side. If meconium is found in the amniotic fluid during the birth, the midwife must make sure she thoroughly cleans out the baby's mouth and throat using suctioning, preferably before the baby takes his or her first breath. This may be done as soon as the head emerges from the vagina and before the body is born. A baby with meconium staining should be professionally examined for meconium aspiration and possibly treated by a health care provider.
Placenta Exam: Succinturiate Lobes, Maternal Side.
Placenta Exam: Battledore Cord Insertion.
Placenta Exam: Placental Circumvallate, Partial and Complete.
Placenta Exam: Placental Abruption With Large Blood Clots.
Placenta Exam: Placental Infarction, Calcified Areas of The Placenta.
MATERNAL CARE FOLLOWING PLACENTAL DELIVERY
The mother is examined after the placenta has been expelled for tears in the vagina or cervix. If an episiotomy has been done, it is repaired at this time (with or without local anesthesia).
Continuing assessments are made on both the mother and infant. Both are cleaned up and made warm and comfortable. Breastfeeding, if not initiated before the expulsion of the placenta, is now usually encouraged. This helps the uterus to remain firm and contracted preventing excess blood loss.
Breast-feeding the infant.
After the delivery of the placenta, the immediate postpartum is considered Stage 4. This is the time when the mother (and infant) are watched over for a few hours or so to make sure all is well.
Long, Phyillis J. Management of the Third Stage of Labor: A Review. Journal of Nurse-Midwifery Volume 31, No. 3, May-June 1986. pp. 135-140. Schuler-Maloney Doris. Placental Triage of the Singleton Placenta. Journal of Midwifery and Women's Health Volume 45, No.2, March-April 2000. pp. 104-113.
DSM PathWorks, Inc: Placental Triage 101 (Continuing Education)
Gray's Anatomy of the Human Body: Fetal Membranes & Placenta Development
NORMAL LABOR & DELIVERY LINKS
Labor Initiation: Getting It Going Introduction to Stages of Labor Stage 1 of Labor & Birth: Contractions, Dilation & Effacement of the Cervix Stage 2 of Labor & Birth: Pushing The Baby Out Stage 3 of Labor & Birth: Delivery of the Placenta Stage 4 of Labor & Birth: Immediately Postpartum
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MoonDragon's Parenting: Placenta Disposal Rituals & Recipes
MoonDragon's Pregnancy Information: Placenta Abruption
MoonDragon's Pregnancy Information: Miscarriage (Spontaneous Abortion)
MoonDragon's Guidelines: Retained Placenta
MoonDragon's Pregnancy: Placenta Previa
MoonDragon Birthing Guidelines Index
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Some photos obtained from "Attending Ob/Gyn Patients" Nursing Photobook by Nursing Books, Intermed Communications, Inc.
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