Chapter 55 - The Placenta Flashcards
Major role of the Placenta
To permit the exchange of oxygenated maternal blood (rich in oxygen and nutrients) with deoxygenated fetal blood.
What circulates blood into the placenta?
Maternal vessels–coursing posterior to the placenta
Blood from the fetus returns to the placenta through what?
The unbilical cord
What 4 things make up the embryonic or fetal membranes?
1-Chorion
2-Amnion
3-Yolk Sac
4-Allantois
Implantaion of the blastocyst occurs
6-7 days after fertilization
Enlargement of the trophoblasts helps to anchor the blastocyst to the
Endometrial lining, or decidua.
2 components of the placenta
1-Maternal portion-decidual BASALIS (formed by the endometriial surface)
2-Fetal portion (developed from the chorion frondosum)
Decidual reaction that occurs between the blastocyst and the myometrium
Decidua Basalis
decidual reaction occuring over the blastocyst closest to the endometrial cavity
Decidua capsularis
A reaction changes in the endometrium opposite the site of implantaion
Decidua vera (parietalis)
The fetal trophoblastic tissue that together with the decidua, forms the area for maternal and fetal circulation
Chorion Frondosum
The chorion around the gestational sac on the opposite side of impantation
Chorion laeve
The fetal surface of the placenta
Chorion Plate
The maternal surface of the placenta
Basal plate
The major functioning unit of the placenta
Chorionic Villus
The maternal blood enters
The intervillous spaces
The decisua capsularis is stretched as
the embryo and membranes grow
The chorinonic villi opposite the implantation site of the chorionic sac gradually
Atrophy and disappear (smooth chorion or chorion laeve)
The maternal surface of the placenta, which lies continuous with the decidua basalis
The basal plate
The fetal surface, which is continuous with the surrounding chorion
The chorionic plate
Before birth, the fetal membranes and placenta perform the following 4 functions and activities
1-Protection
2-Nutrition
3-Respiration
4-Excretion
The fetal membranes and placenta sepatate and are expelled
at birth or parturition
Oxygen rich blood passes through the umbilical vein into the ________ through the _________ into the _____ to the______across the _______ into the ________, blood then passes into the _______ and out the ________ to supply the _____ and _______.
fetal abdomen
ductus venosus
IVC
RT Atrium
Foramen Ovale
Lt Atrium
Lt Ventricle
Ascending AO
Brain
Upper body
Un-oxygenated blood from the SVC passes into the _____ through the ______ and across the ________, most blood passes through the _______ and into the _______ to the ________, the _______ to the _______ to return to the ______ for respiratory and nutrients exchange.
Rt Atrium
RT Ventricle
Main Pulmonary Artery
Ductus Arteriosus
AO Arch
Descending AO
Internal Iliac Arteries
Unbilical Arteries
Placenta
What is dedicated to the survival of the fetus
The Placenta
What happens when the fetus is exposed to a poor maternal environment
The placenta can often compensate by becoming more efficient
If the fetus is exposed to poor maternal environment that is severe enough, the stresses can lead to
placental damage
fetal damage
intrauterine demise and pregnancy loss
3 conditions that decrease uterine blood flow and may reduce maternal placental circulation
1-severe hypertension
2-renal disease
3-placental unfarction
Placental defects can cause
IUGR
The normal attachment of the cord is usually
Near the center of the placenta
insertion of the umbilical cord at the margin of the placenta, within 10mm of the edge
Battledore Placenta
A membranous insertin and is best demonstrated with color doppler.
If the membranes cross the internal os it is known as.
Velamentous Placenta
Vasa Previa
Normally the placenta will implant on the
Anterior, fundal or posterior wall of the uterus
Occasionally the placenta will implant low in the uterus resulting in a condition called
Placenta Previa
The Chorion originates from the
Trophoblastic cells
The Amnion develops at the
28th menstrual day
The amnion fuses with the chorion and can no longer be seen on ultrasound as two separate membranes by
16 weeks
The functional endocrine units of the placenta
Chorionic villi
A central core of the placenta is surrounded by an _________ and an__________
Inner layer (cytotrophoblast)
Outer layer (syncytiotrophoblast)
The inner layer (cytotrophobast) of the placenta produces
Neuropeptides
The outer layer (syncytiotrophoblast) of the placenta produces
The protien hCG
human placenta lactogen (hPL)
the sex steroids, estrogen and progesterone
The function of hCG
to maintain the corpus luteum in early pregnancy
hPL is responsible for
The promotion of lyplysis and an antiinsulin action that serves to direct nutirents to the fetus
Progesterone production is
exclusively a maternal-placental interaction, with no contibution from the fetus
The placenta is identified on sonography as early as
8 menstrual weeks
The substance of the placenta assumes a relatively __________ pebble-gray appeaarance between______ and is easily recognized with its characteristically _______ borders
Homogeneous
8-20 weeks
Smooth
The fetal surface of the placenta (portion closest to the fetus) is represented by the
Echogenic chorionic plate
The second surface which lies at the junction of the myometrim
Basal plate
Maternal bloos vessels from the endometrium run behind the basal plate and are often confused with
Placental abruption
The thickness of the placenta varies with gestational age with a diameter of
Less than 2-3cm in fetuses greater than 23 weeks.
The size of the placenta corresponds to the
Gestaional age. And rarely exceeds 4cm
When evaluating the thickness you should maintain a
Perpendicular measurment of the placental surface in relation to the myometrial wall
Enlarged placentas may also be associated with
Rh sensitization
Diabetes of pregnancy
congenital anomalies
Cystic structures representing large fetal vessels are commonly observed coursing
Behind the chorionic plate and between the amnion and chorion layers
(Several sonolucent areas within the placenta may confuse you while unfamiliar with the wide range of placental variants)
Sonographic evaluation of the normal placenta
A- amniotic fluid
f- fetus
P- placenta
Real time observation of blood flow or color Doppler helps to differentiate these vessels
______ may also be found in th eintervillous spave posterior to the chorionic plate (subchorionic)
Deposits of fibrin
May also be seen within the placental substance
Placental sonolucencies.
(These have been refered to as placental lakes and are most often a normal finding)
The placenta is separated from the myometrium by
A subplacental venous complex
Transverse image of the placenta as it lies along the anterior uterine wall. Sonolucencies are seen representing placental lakes (arrows).
A thin hypoechoic layer posterior to the basilar vein
The myometrium
These veins can become very prominent and should not be confused for a retroplacental or marginal hemorrhage
Basial and marginal
To evaluate the position and size of the placenta you should scan
longitudinally from side to side and transversely from inferior to superior
While scanning the placenta what should be documented
the insertion of the cord and inferior edge of the placenta
The placenta may be seen along the
fundus, anterior or lateral uterine wall
The location of the placenta can change framatically with
an over distended urinary bladder or focal uterine contractions.
________ should not be confused for aplacental pathology, The appearance of these contractions may distort the uterine contour and the suspicious area may be rescanned after 15-20 minutes to see if the uterine contour has returned to normal.
Braxton Hicks contractions
The position of the placenta should be described with
Specific na,es given to it by it’s point of origin.
Fundal/Anterior
Fundal.Posterior
Left Lateral, etc….
To visualize the internal os of the cervix and see the relationship of the placenta to the internal os
A sagittal image of the lower uterine segment (LUS) and cervix should be obtained
A normally implanted placenta may appear to cover the internal os if
The maternal bladder is over filled.
(Emptying the bladder reduces the pressure on the lower uterine segment and allows the cervix to assume a more normal position but makes it difficult to see the cervix)
Diagnosis of a posterior previa may be dificult because the fetal skull bones block transmission if the
Fetal head is low in the pelvis.
(You may try tilting the patient in a slight Trendelenburg’s position or using the endovaginal or transperineal approach to relieve pressure of the uterus on the lowe uterine segment-LUS-)
Especially when evaluating the inferior edge of the placenta the best imaging tool to identify the lower uterine segment is
Transvaginal sonography
LUS-lower uterine segment
A previa noted on a scan alerts the obstetrician the
no pelvic exam should be performed.
(A finger inadvertently pushed through an unknown previa can cause bleeding)
A placenta noted to be low-lying early in pregnancy can be followed with
consecutice scans to see whether it persists
When the placenta appears to lie on both anterior and posterior uterine walls, check for
A laterally positioned placenta
When the placenta doesn’t appear to connunicate a
Succenturiate placenta should be considered
This is a condition in which there are additional placental lobes jointed to the main placenta by blood vessels
Succenturiate plcenta
A, Placenta (P) appears to be located on both anterior and posterior uterine walls. c, Umbilical cord.
B, By scanning laterally, the placenta is seen to communicate (arrow), representing a lateral placenta rather than a succenturiate lobed placenta
A clinician should be notified of the condition, Succenturiate placenta because
There is a risk that these connecting blod vessels may rupture or that an extra lobe may be inadvertently left in the uterus after delivery
The concept that the placenta changes its position within the uterine cavity has been termed __________,implying that the placenta actually moves and relocates
Placental migration.
(It may be that the placenta actually does not move, but the position appears changed because of the physiologic enlargement of the uterus and development of the lower uterine segment)
A placenta previa should not be diagnosed before
20 weeks
If the placenta is a complete previa in the _______________ it is unlikely to change it’s position drastically
Early 2nd trimester
If the placenta is a complete previa in the _______________ it will most likely remain a complete previa
3rd trimester
PLacental function can be assessed by
Color, power and pulsed doppler
The Uterine artery should a ________ flow pattern in the 1st trimester, and should become a _________ flow pattern in the 2nd trimester
High-resistance
Low-resistance
In the 1st trimester, the flow velocity waveform shows a notched appearance in diastole; this notch usually disappears by
24 weeks
In the 2nd trimester, the doppler signals of the ________ are variable depending on the location of the placenta with the lowest reistance on the __________
Uterin Arteries
Placental side
4 Normal characteristics of a normal placenta at delivery
1- measures about 15-20cm in diameter
2-Discoid in shape
3- Weighs about 600g
4- Measures less than 4cm in thickness
The placenta should be evaluated to have been delivered intact to prevent complications of
postpartum hemorrhage or infection
Membranes of the amnion and chorion are inspected for
Color and consistency, with attention to meconium staining or signs of infection
Short umbilical cords, less than 30cm, may result in
Traction during labor and delivery, leading to tearing of the cord, abruption or inversion of the uterus
Long umilical cords are more likely to
Prolapse, become twisted around teh fetus, or tie in true knots
A protein found throughout the placenta but is most pronounced in the floor of the placenta and increases continuously throughout pregnancy.
Fibrin. Wich is derived from fibrinogen
On ultrasound, this fibrin deposition appears as hypoechoic area beneath the
chorionic plate of the placenta
Differential consideration of fibrin deposition (subchorionic) includes
A venous lake or a subchorionic hematoma
The mayjor pathologic processes seen in the placenta that can adversely effect pregnancy outcome include
1- Intrauterine bacterial infections
2- Decreased blood flow to the placenta
3- Immunologic attack of the placenta by the mother’s immune system
Intrauterine infections can lead to
Severe retal hypoxia as a result of villus edema (fluid buildup within the placents)
__________ decreases in blood flow to the placenta can cause severe fetal damage and even death
Chonic and acute
Other insults that can adversely affect pregnancy outcome by affecting the function of the placenta
1- placental separation
2- cord accidents
3- trauma
4- viral and parasitic infections
An enlarged placenta weighing more than 600g and measures more than 4cm
Placentomegaly
Primary causes for placentomegaly
Maternal diabetes and Rh incompatibility
The implantation of the placenta over the internal cervical os
Placenta previa
The placenta normally implants
In the body of the uterus
___ in ____ pregnancies the placenta implants over or near to the internal os
1 in 200
The placenta may be considered
1-complete or total previa
2-partial previa
3-marginal previa
4-low-lying
The cervical internal os is completely covered by placental tissue
Complete Previa
Placental tissue only partially covers the internal os
Partial previa
Placental tissue does not cover the os, but its edge comes to the margin of the os
Marginal previa
Placenta is implanted in the lower uterine segment but the edge does not reach the os
A low-lying placenta
Complete previa as evidenced by 3cm between maternal sacrum and the fetal head
Ultrasound clearly shows the internal os of the cervix (arrows). The placenta is implanted away from the os
A pregnancy is at high risk because of the risk of a life-threatening hemorrhage when complicated by
Placenta previa
As the pregnancy progresses into the 3rd trimester, two very important changes occur
1-The lower uterine segment is developing (thinning & elongating in preparation for labor)
2-The cervix softens and somw dilation can occur
(Cervical dilation may also disrupt the attachment of a placenta located over or near the os)
7 risk factors associated with placenta previa
1-Advanced maternal age
2-smoking
3-cocaine use
4-prior placental previa
5-multiparity
6-prior cesarean section
7-uterine surgery
5 Complications of placenta previa
1-premature delivery
2-life-threatening maternal hemorrhage
3-increased risk of placenta accreta
4-increased risk of postpartum hamorrhage
5-IUGR
In the 3rd trimester, clinically the patient may present with
painless, bright-red vaginal bleeding
what percent of patients present with bleeding during the forst 30 weeks
25%
Because the treatment will be different based on the clinical diagnosis, a diagnosis is imperative when
a patient presents with 3rd trimester bleeding
If a diagnosis of previa is given, the fetus is preterm and themother is not bleeding heavily, the management may be
bed rest
maternal transfusion (if necessary)
close observation
______ is needed in the majority of previa cases
Cesarean section
with ___________ previas, a minority of patients may deliver vaginally
MArginal placental previa
If the fetus is in a cephalic presentation in the last trimester of pregnancy, examine
the fetal head in relationship to the posterior wall of the uterus and the mother’s sacrum
(A distance of less than 1.5cm indicates there will not be enough room for the placenta to be between the fetal head and posterior uterine wall)
If there is any question of a placenta previa transabdominally, then the patient should be evaluated with
transvaginal sonography
_________ is a potentially life-threatening fetal complication of the placenta that occurs when large fetal vessels run in the fetal membranes across the cervical os, placing them at risk of rupture and life-threatening hemorrhage
Vasa previa
The two most common occurrences of vasa previa are
1-Velamentous insertions of the umbilical cord into the placental membranes, which cross the cervix
2-When a succenturiate love is present, and the connecting vessels course over the cervix
Transabdominal succenturiate
Vasa previa is diagnosed with sonography when
the implanted fetal umbilical vessels are seen to cover the cervix
(color doppler and endovaginal sonography allow visualization of these vascular structures as they cover the os)
3 variants of abnormal penetration of placenta beyond the endometrial lining
1-Plaventa Accreta
2-Placenta Increta
3-Placenta Percreta
(Hint: the severity gets worse alphebetically)
The chorionic cilli attach to the myometrium without muscular invasion
placenta accreta
Chorionic villi attach extending further into the myometrium
Placenta increta
Chorionic villi penetrate through the uterus
Placenta percreta
The risk of placenta accreta increases in patients with
placenta previa and uterine scar from a previous C-section
The of placenta increta is
10-25% in woman with one previous c-secion (when the placenta is implanted over the scar)
Exceeds 50% in women with placenta previa and multiple c-section deliveries
Placenta increta results from the
1-underdeveloped decidualization of the endometrium
2-the association of placenta previa reflects the thin, poorly formed decisuas of the LUS and offers little resistance to deeper invasion by trophoblasts
3-the previous cesarean scar permits the trophoblastic invasion
High maternal mortality and morbidity are associated with
Placenta increta.percreta, so an accurate pernatal diagnosis is critical
Almost all cases of placental invasion have an _________ in a women with prior c-section
Anterior previa
(Pay careful attention to the placenta and myometrium in any patient with a placental previa and prior history of cesarean. There is usually a loss of the normal interface between the placenta and myometrium)
angle the transvag probe ______________ to evaluate the uterine-bladder interface
toward the urinary bladder
You should evaluate the placenta previa to look for the absenece of
hypoechoic subplacental venous channels and myometrium beneath the placenta
the placental vessels extend within the urinary bladder in
Placenta percreta
The presence of one or more accessory lobes connected to the body of the placenta by blood vessels
Succenturiate placenta
The retention of the succenturiate lobe at delivrey may result in
postpartum hemorrhage or infection
With succenturiate placenta look for a
discrete lobe that has “placenta texture” but is sparate from the main body of the placenta
with color flow doppler of a succenturiate placenta
vascular bands are seen connecting the lobes
The succentturiate placenta varies in appearance; it may be
as large as the main lobe and appear as two placentas
The attachment of the pacental membranes to the fetal surface of the placenta rather than to the underlying villous placental margin
A circumvallate/circummarginate placenta
A circumvallate placenta is diagnosed when the placental margin is
folded, thickened or elevated with underlying fibrin and hemorrhage
_______ may occur within or around the placenta and is more commonly seen than a placental abruption
Placental hemorrhage
refers to bleeding from the placenta from any cause
Placental hemorrhage
4 locations of placental hemorrhage
1-retroplacental
2-subchorionic
3-subamniotic
4-intraplacental
If bleeding subsides hemorrahges are more likely to resolves within
the 1st trimester
The sonographic appearance of placental hemorrhge varies greatly with the
location
size
and age or onset of the hemorrhage
If a hemorrhage is present, the echogenicity depends on the age of the hemorrhage;
an acute bleed-is similar to the echogenicity of the placenta
Subacute and chronic bleed-becomes more hypoechoic
(a poor outcome is expected if fetal bradycardia is present)
The separation of a normally implanted placenta before term delivery
Abruptio placenta or placental abruption
Placental abruption is a premature placental detachment and occure in
1 in 120 pregnancies
Bleeding in the __________ occurs with separation
dicidua basalis
Ultrasound showing an abruption. Arrows point to the echolucent collection of blood lateral to the edge of the placenta. P, Placenta
The detection of acute abruptions is more difficult because
the medium level echogenicity makes them isoechoic to placental tissue
__________ may be further classified as retroplacental or marginal
Abruptio placenta
An expanding hematoma can lead to loss of surface area, placing the fetus at risk for
hypoxia and even sudden fetal death
9 risk factors for placental abruption
1-Maternal hypertension (seen in 50% of severe abruptions)
2-Prior abruption
3-Short umbilical cord
4-Uterine anomaly
5-Myomas
6-Abdominal trauma
7-Placenta previa
8-Tobacco use
9-Cocain use
Results from the rupture of spiral arteries and is a “high pressure” blees
Retroplacental abruption
Is associated with hypertention and vascular disease
retroplacental abruption
(If the blood remains retroplacental, the patient has no visible bleeding)
the most common type of abruptions and are also known as subchorionic bleeds.
Marginal abruption
This type of abruption results from tears of the marginal veins and represents a “low pressure” bleed
Marginal abruption
This type of abruption arises from the edge of the placenta, dissects beneath th eplacental membranes and is associated with little placental detachment
MArginal abruption
Results from intraplacental hemorrhage cause by breaks in the villous capillaries.
Usually there is little risk to the fetus, although the condition is associated with Rh sensitivity and elevated alpha-fetoprotein levels
Intervillous thrombosis
The presence of thrombus within the intervillous spaces occurs in
one third of pregnancies
On ultrasound sonolucencies are seen within the homogeneous texture of the placenta
Intervillous thrombosis
The inhomogeneity of the placenta is seen with sonolucent areas within the texture of the placenta (arrows).
Discrete lesions caused by ischemic necrosis
Placental infarcts
(large infarcts may reflect underlying maternal vascular disease)
Common and found in 25% of pregnancies, are usually small with no clinical significance
Placental infarcts
Commonly known as molar pregnancy; they may be benign or malignant
Gestational trophoblastic disease
3 gestational trophoblastic diseases
1-complete or partial mole
2-choriocarcinoma
3-invasive
Clinical symptoms of a gestational trophoblastic disease
1-extreme nausea and vomiting (from elevated hCG levels)
2-vaginal bleeding
3-uterine size larger than dates
Generally have a diploid karyotype and have no fetal tissue
Complete moles
Usually have a triploid karyotype and fetal tissue is often present
Partial or incomplete moles
Ultrasound will show a uterus that is larger than dates, no indentifiable fetal parts and an inhomogeneous texture with various-sized cystic structures within the placenta
Bilateral theca lutein cysts are seen in the ovaries secondary to the hyperstimulation of the elevated hCG
complete mole
carries little malignant potential, is associated with an abnormal fetus or fetal tissue.
On ultrasound a reduced amount of amniotic fluid is noted without defined fetal parts, the placenta is thick with multiple intraplacental cystic spaces
Partial mole
A benign vascular tumor of the placenta, large tumors can act as arteriovenous malformations shunting blood from the fetus causing complications
Chorioangioma
2nd to trophpblastic disease, _________ is the most common “tumor” of the placenta
Chorioangioma
6 complications with Chorioangioma
1-polyhydramnios
2-fetal hydrops
3-fetal cardiomegaly
4-IUGR
5-fetal demise
6-preterm labor (large chorioangiomas)
Ultrasound exam shows a circumscribed solid or complex mass that protrudes frome the fetal surface of the placenta, it may be located near the unbilical cord insertion site
Chorioangioma
A Chorioangioma larger than ______ are usually detected prenatally and are more likey to have complications
5cm
When a placental mass is seen look for
polyhydramnios
hydrops
IUGR
and signd of anemia
3 differential considerations for solid placental masses include
1-partial hydatidiform mole
2-teratoma
3-maternal tumor metastic to the placenta
