The placenta evolves both structurally and functionally throughout pregnancy. In the first half of the 1st trimester, the embryo develops in an environment with a lower oxygen concentration. The formation of villi begins around day 13 after conception; fetal placental capillaries are detectable by 3 weeks post conception . A transudate from maternal plasma bathes the trophoblastic plugs2. A true intervillus blood flow is not well established until 12 weeks' gestation . By 14 weeks' gestation uterine artery velocity increases; there is continuous intervillous flow; and end diastolic flow appears in the umbilical artery3. The eventual position and shape of the normal placenta is due to the degeneration of villi from all areas, except those with the best blood supply. As a result, villi in the lower uterine segment tend to atrophy, while villi develop within the uterine fundus. This process is referred to as trophotropisim
ransvaginal scan at 8.5 weeks shows an early placenta (P) with chorion laeve opposite (open arrow). F, fetus; arrow, yolk sac; arrowhead, amnion. At this stage, the amniotic sac is smaller than the chorionic cavity, and the amniotic membrane is visible at sonography. The amnion and chorion fuse at approximately 12 weeks.
Fetal side of placenta will have chorionic plate and chorionic villi Maternal side : Decidua basalis Villi have a surface area of 12 – 14 m2..
Size of the placenta increases linearly with CRL
Retro placental area : myometrium and decidua hypoechoic to placenta, draining veins along length of maternal surface, spiral arteries may be visible
Texture : echoes form branching villi bathed in maternal blood in the intervillous space produce diffuse granular echotexture of the placenta : this remains constant throughout gestation except for calcification.
Marginal sinus of placenta where intervillous blood drains into maternal circulation should not be confused for placental separation
microscopically during the first two trimesters and becomes macroscopic at about 29 weeks.
produce the diffuse granular echotexture of the placenta. This texture remains constant throughout gestation. The most notable exception is calcium deposition. Placental calcium deposition is a physiologic process that occurs microscopically during the first two trimesters and becomes macroscopic at about 29 weeks. It may be found along the basal plate, in the intraplacental septa, and in collections of fibrin in the intervillous and subchorionic spaces (Fig. 8-4 ). Chemical, radiographic, and sonographic studies have shown an exponential increase in placental calcification with increasing gestational age;(9-12) more than 50% of placentas contain some degree of calcification after 33 weeks.(11,12) Placental calcification is more common in women of lower parity,(11,12) and it is not increased in postmature placentas.(1,9,10,11) Placental calcification is of no known clinical significance;(1,2) it is not useful to grade placentas according to calcium content.
Grade 0: Placental body is homogeneous. The amniochorionic plate is even throughout. Late 1st trimester-early 2nd trimester
Grade I : Placental body shows a few echogenic densities ranging from 2-4 mm in diameter. Chorionic plate shows small indentations. Mid 2nd trimester �early 3rd trimester (~18-29 wks).
Grade�II : Chorionic plate shows marked indentations,creating comma-like densities which extend into the placental substance but do not reach the basal plate. The echogenic densities within the placental also increase in size and number. The basal layer comes punctuated with linear echoes(dot dash configuration) which are enlarged with their long axis parallel to the basal layer. Late 3rd trimester (~30 wks to delivery)
Grade III : Complete indentations of chorionic plate through to the basilar plate creating �cotyledons� (portions of placenta separated by the indentations) . 39 wks � post dates
Grade 3 /premature calcification : smoking. Iugr and htn sle dm, sig placental dysmaturity/insuff +iugr Less specific for dating and asssessing lung maturity
MR imaging is generally not performed during the first trimester, owing to theoretical concerns for the safety of the fetus and early stage of placental development.
The uteroplacental unit is of uniform, intermediate signal on unenhanced T1-weighted images, affording no opportunity to distinguish the placental-myometrial interface or to examine myometrial architecture.
Following contrast administration, the placenta heterogeneously enhances before the uterus, and becomes more homogeneous over time. Contrast-enhanced MR imaging has been advocated as a means to better delineate the myometrial-placental interface, leading to more accurate assessment of the depth of invasion. Although gadolinium-based contrast agents have not been definitively shown to have detrimental effects on the human fetus, these contrast agents do cross the placenta and are generally avoided unless the potential risks to the patient are outweighed by the potential benefits of contrastenhanced imaging.
. Succenturiate lobe. Axial single-shot fast spinecho image in a 40-year-old woman demonstrates the succenturiate lobe (S), clearly separate from the main placenta (P).
Maternal surface of the placenta after delivery. Four succenturiate lobes (arrows) were connected to the main placenta (P) by vessels.
ROLLED EDGE OF MEMBRANES AT PLACENTAL CHORIONIC DISC – PLACENTAL SHELF NOT TO BE CONFUSED WITH UTERINE SYNECHAEI, SEPTAE, AMNIOTIC BANDS.
Other abn of shape: Instead of disc, can be 1. bidiscoidal 2. lobed 3. diffuse(membran/annular) 4. succentruria 5. fenestrated – hole in disc 6. circumvalate
contraction involving the anterior placenta (P). The retroplacental myometrium shows a hypoechoic "pseudomass" (arrows). The myometrium of the posterior wall of the uterus appears smooth and thin (arrowhead)
After 20 minutes, the anterior placenta (P) appears smooth and the retroplacental myometrium is uniform and thin (arrows). The contraction involves the posterior myometrium (arrowhead) .
Except for the subchorionic space, most areas of the placenta are densely packed with villi. Blood tends to pool and eddy in the subchorionic space. Plaques of laminated subchorionic fibrin are found in about 20% of placentas from uneventful pregnancies.(1) These plaques correlate with subchorionic anechoic-hypoechoic lesions (Fig. 8-6, Fig. 8-7A and Fig. 8-7B ), which may be seen at sonography as early as 12 weeks.(13) They usually decrease in size during the course of the pregnancy, as fibrin is laid down. Slow flow is often visible at real-time sonography; in many such lesions, color Doppler imaging fails to demonstrate flow.
Subchorionic fibrin deposition. Sector scan at 17 weeks shows a hypoechoic subchorionic area (arrows); the echoes within denote slow flow. This lesion correlated with subchorionic fibrin deposition at delivery. Subchorionic fibrin deposition. Sagittal scan of the posterior placenta (P) at 29 weeks shows prominent 4x9 cm hypoechoic sub chorionic lesion (cursors) containing areas of slow flow. A vessel is seen adjacent to the lesion (arrow). Corresponding slice of term placenta shows that the lesion is composed of laminated fibrin (arrow) and blood (open arrow).
Perivillous fibrin deposition is caused by pooling and stasis of blood in the intervillous space. It is found in 25% of placentas from uncomplicated term pregnancies and has no clinical significance.(1) Often, a hyperechoic rim is seen around these lesions at sonography, caused by compression of the villi bordering the lesion.Up to 40% of term placentas from uncomplicated pregnancies contain intervillous thromboses;(2) these lesions result from fetal hemorrhage into the intervillous space. Intervillous thromboses are not considered clinically significant. Because they are a site of fetal bleeding into the maternal circulation, however, such lesions possibly could lead to isoimmunization.Septal cysts are another anechoic intraplacental lesion that may be seen at antenatal sonography.(17) These cysts measure 5 to 10 mm in diameter and are found in up to 19% of term placentas from uncomplicated pregnancies(1) (Fig. 8-10 ). They occur at the apex of placental septa
However, extensive infarction involving more than 10% of the villi has been associated with intrauterine growth rate retardation, fetal hypoxia, and fetal demise.(2) In these situations, the underlying maternal vascular disorder is the root of the problem. Infarcts cannot be identified at sonography unless they are complicated by hemorrhage,(17) probably because infarcts contain necrotic villi, whereas the anechoic-hypoechoic lesions described previously contain blood, fibrin, or fluid.
Placenta previa refers to a placenta that covers part or all of the internal os of the cervix (Fig. 8-23 ). It occurs in less than 1% of deliveries and necessitates a cesarean section. The incidence of placenta previa is higher in older mothers and in women who smoke Placenta previous to fetus in birth canal: bleeding fatal; digital exam hazard In mid-gestation the placenta occupies 50% of the uterine surface. By 40 weeks' gestation, the placenta occupies 17 - 25% of the uterine volume 14 ..
low-lying placentas identified during the second trimester are not in the region of the cervix at delivery, as the placenta is thought to grow preferentially toward the well vascularized fundus, with atrophy of the placental segment near the less vascular cervix
COMPLETE SYM/ASYM AND AFTER VOIDIDNG
Complete placenta previa. Sagittal single-shot fast spin-echo image of a 28-year-old woman shows the placenta completely covering the internal cervical os. Placenta percreta was also present. At delivery, the bladder was not invaded but was adherent to the placenta.
Low-lying Placenta Transvaginal sonography has been used to define a low-lying placenta as < 2.0 cm from the internal cervical os 20 (Fig. 6). Openheimer et al 7 of 8 patients with a placental edge < 2 cm from the internal cervical os required a cesarean section for bleeding. The only patient in this group who did not have a cesarean section had a scan to delivery interval of 11 weeks . If the lower edge of a low-lying placenta is thick (> 1 cm) there is a higher risk of hemorrhage, emergency cesarean section and placenta accreta.
1ST WITH MYOMETRIAL CONTRACTION
In normal : villi attach to decidua : cytotrophoblasts invade as far as the first third of the myometrium . . In placenta accreta, the chorionic villi directly contact, but do not invade, the uterine wall. In placenta increta, chorionic villi invade the myometrium but do not reach the serosal layer. In placenta percreta, the chorionic villi invade through the myometrium to reach or extend beyond the uterine serosa, with possible invasion of adjacent structures such as the bladder or pelvic side wall.
In placenta accreta, the normally hypoechogenic, 1- to 2-cm area is absent or markedly thinned (< 2 mm), there is loss of the normal decidual interface between the placenta and myometrium. thinning or disruption of the hyperechogenic uterine serosa-bladder interface may be seen as well as the presence of focal exophytic masses. prominent hypoechogenic–anechoic spaces (lacunae) in the placenta marked periplacental vascularity on color Doppler sonography. Guy et al. The presence of lacunae, within the placental parenchyma, particularly when numerous and concentrated in the lower uterine segment, appears to be a separate risk factor for placenta accreta, f
The placenta is low lying and anterior with placenta previa often present (Fig. 7.14). The retroplacental complex of vessels is partially or completely absent. Care must be taken to avoid compression of these vessels by excessive transducer pressure or bladder overdistention. The myometrium underlying the placenta appears thinned (<1 mm) or absent. The bright reflection of the serosa separating the uterus from the bladder is absent. Color Doppler may show contiguous blood vessels extending from the myometrium into the bladder wall (Fig. 7.14B). The abnormal blood vessels may cause focal elevations of the bladder mucosa.
Although the definitive treatment for placenta accreta is a hysterectomy, conservative management of placenta accreta is possible. Conservative management, particularly for those patients who wish to preserve fertility includes: curettage, oversewing of the placental bed, and ligation of the uterine arteries or the anterior divisions of the internal iliac arteries
Although definitive management includes planned cesarean section hysterectomy, some institutions request interventional radiology to place embolization or balloon catheters in the internal iliac arteries prophylactically, to be used if necessary.39 Other approaches to reduce maternal morbidity include segmental myometrial resection or leaving the placenta within the uterus following delivery, and treating with methotrexate or uterine artery embolization.
Coronal single-shot fast spin-echo image of a 38-year-old woman at 35 weeks gestational age demonstrates a lateral bulge (arrows) in the placenta (P) and lack of identifiable subjacent myometrium at the site of prior resection of a rightsided rudimentary uterine horn. Without the history of prior surgery in this area, this would be an unusual location for abnormal placentation.
(A) Axial single-shot fast spin-echo image through the uterus in a 33-year-old woman with a history of prior myomectomy and complicated pregnancy. The 11-week placenta is attached at the myomectomy site (arrow). Concern for abnormal placentation and risk of retained products was conveyed to the referring obstetrician. Note a subserosal leiomyoma (L). (B) Axial gadolinium-based contrast-enhanced, T1-weighted, fat-suppressed axial image through the uterus after the patient spontaneously aborted, demonstrating retained products of conception (arrow) at the prior site of abnormal placentation.
. Placenta percreta. Coronal HASTE image of a 30-year-old woman with history of 2 prior cesarean sections, imaged in the third trimester. No normal myometrium is seen beneath the placenta. Note the deformity (outward bulge) of the uteroplacental complex (arrows).
Placenta previa and placenta percreta in a 25-year-old woman at 21 weeks gestational age. (A) Sagittal single-shot fast spin-echo image shows widening (hourglass appearance) of the lower uterine segment (black and white arrows). (B) Sagittal steady-state free-precession image at a slightly different location shows a markedly heterogeneous placenta (P) that contains several dark intraplacental bands (arrow).
Placenta accreta in a 36-year-old woman at 31 weeks gestational age. Sagittal single-shot fast spin-echo image through the uterus shows loss of the normal layered myometrium in the lower uterine segment (arrow) with focal bulge of the placenta, without distortion of the myometrial contour. Placenta accreta was found at delivery.
Heterogeneous placenta with dark placental bands and vessels. (A) Axial single-shot fast spin-echo image through the placenta shows a heterogeneous placenta (P). The distinction between placental bands and vessels is not clear on this sequence. (B) Axial steady-state free-precession sequence shows the vessels to be high signalintensity structures (arrow).
HYPOECHOIC LESION DEEP TO THE LATERAL MARGIN OF THE PLACENTA REPRESENTING A SUBCHORIONIC/MARGINAL PLACENTAL HEMATOMA
RELATIVELY HYPOECHOIC LESION IN SUBCHORIONIC AREA S/O SUBCHORIONIC HEMATOMA. ABSENCE OF FLOW IN THE REGION OF THIS HEMATOMA. Aka submembranous hematoma
Subchorionic hemorrhage. Axial T1-weighted, fat-suppressed gradient echo image shows a high signal-intensity rim (arrow) surrounding the uterine cavity. A subserosal leiomyoma (L) is also present.
MASSIVE SUBCHORIONIC HEMATOMA FROM FETAL VESSELS (FETAL SURFACE) USUALLY WITH IUGR
A sub-amniotic hemorrhage is contained within amnion and chorion and thus extends anteriorly to placenta but is limited by reflection of amnion on placental insertion site of umbilical cord. They may sonographically be detected as a poorly reflective oval-shaped cystic mass overlying the fetal plate of the placenta and covered in a thin membrane
LARGE RETROPLACENTAL HEMATOMA SHOWN BY USG WITH SIGNIFICANT ELEVATION AND DETACHMENT OF POSTERIOR PLACENTA FROM THE UTERINE WALL IN A PATIENT WITH BLEEDING PV.
Placental abruption (also called abruptio placentae) refers to bleeding at the decidual-placental interface that causes partial or total placental detachment prior to delivery of the fetus. The diagnosis is typically reserved for pregnancies over 20 weeks of gestation. The major clinical findings are vaginal bleeding and abdominal pain, often accompanied by hypertonic uterine contractions, uterine tenderness, and a nonreassuring fetal heart rate (FHR) pattern
The sensitivity of an ultrasound examination for detecting placental abruption is between 25% and 50%
35 weeks shows a large hyperechoic retroplacental hematoma (arrows). P, placenta; F, fetus. The patient was hypotensive, with acute vaginal bleeding. At cesarean section, a 75% abruption was found.
Placenta previa with subacute subchorionic hemorrhage in a 22-year-old woman at 31 weeks gestation. (a) Sagittal transvaginal gray-scale US scan is suggestive of the presence of placenta previa. (b, c) MR images correctly depict the presence of subchorionic hematoma (long arrows). Sagittal T1-weighted gradient-echo image (b) (repetition time msec/echo time msec = 4.1/1.1, 10° fl ip angle) shows the hyperintense subchorionic hematoma located above the internal os. The clot is hyperintense on the sagittal diffusion-weighted image (b value, 800 sec/mm2 ) (c). The placenta (short arrow in b and c) has normal signal intensity
Placental Chorioangioma Chorioangioma is a benign tumor of the placenta sometimes classified as a hamartoma. They are found in 1% of placentas pathologically but most are small and not clinically significant . US detects only the larger lesions which are associated with elevation of maternal serum alpha-fetoprotein (MS-AFP). Hypo to hyper echoic well defined, on fetal surface Chorioangiomas appear as well-defined, hypoechoic, or mixed echogenicity masses within the placenta, often near the cord insertion site (Fig. 7.15) . Detected chorioangiomas are usually 1-5 cm in size. Spectral Doppler is diagnostic with demonstration of vessels within the tumor with blood flow pulsating at fetal heart rate. Placental hematomas may have a similar appearance but have no blood flow on Doppler US.
No adequate vascularisation, no abn proliferation of trophoblasts BHCG > 1 lakh m iu/ml, normal preg <60,000
Hydatidiform mole. Sagittal scan shows an enlarged uterus filled with solid material containing multiple small anechoic lesions. This is the typical appearance of a hydatidiform mole.
Hydatidiform mole with coexistent fetus. Sector scan at 13 weeks shows a large anterior mass (arrows) containing multiple anechoic vesicles of varying sizes, along with a fetus (F) and a separate posterior placenta
Persistent trophoblastic disease (choriocarcinoma and invasive mole) occurs in about 10% of patients with hydatidiform mole. Triploid as well as nontriploid partial moles have also developed into persistent trophoblastic disease requiring chemotherapy.(21-24) Thus, monitoring serum B-human chorionic gonadotropin levels in all patients with any form of hydatidiform mole is important.
Velamentous cord insertion in a 32-year-old woman during third trimester of pregnancy. Sagittal (A) and coronal (B) single-shot fast spin-echo images through the uterus demonstrate insertion of the umbilical cord (arrows) into the fetal membranes remote from the placenta
Vasa previa can be of two types type I (present in ~ 90% of cases with vasa previa 3) : abnormal fetal vessels connect a velamentous cord insertion with the main body of the placenta or type II : abnormal vessels connect portions of a bilobed placenta, or a placenta with a succenturiate lobe : due to this association, vasa previa needs to be excluded in patients with variant placental morphology.
Sonographic features are considered generally specific (~ 90%) 2. The diagnosis is often made with trans-abdominal Doppler sonography demonstrating flow within vessels which are seen overlying the internal cervical os. Occasionally a trans-vaginal scan is required to aid better visualisation of aberrant vessels. Non Doppler (grey scale) images may suggest the diagnosis if there are echogenic parallel or circular lines within the placenta near the cervix. Complications These vessels are unsupported by Wharton jelly or placental tissue and are at risk of vascular rupture in event of supporting membrane rupture a vessel rupture can result in a catastrophic fetal haemorrhage and often an emergency Caesarian section is required in this situation. direct injury during labour.
Radiological evaluation of the Placenta
Dr Lenon J. D’Souza
EVALUATION OF THE
The early gestational sac is first
visible at transvaginal
sonography at about 4 weeks'
Its hyperechoic rim contains
developing villi composed of
fetal vessels surrounded by the
lacunar space, which is the
precursor of the intervillous
At about 5 weeks' menstrual
age, those villi situated
opposite the implantation site
begin to atrophy, forming a
smooth surface (chorion
The remaining villi, the
chorion frondosum, become
the placenta, which may be
identified at sonography at
about 8 weeks
Placental lakes represent inter villous space devoid of
placental villous trees
Hypoechoic structures with evidence of blood flow
Well formed by around 12 weeks
Most commonly assessed at 18-20 weeks
THINGS TO ASSESS:
SIZE- >1 cm not >4 cm thick within 24 weeks
N : anterior/posterior /fundal
RETROPLACENTAL AREA= N :hypoechoic
CORD : SITE OF INSERTION (centre or within 2 cm)
NO. OF VESSELS ( N = 3)
Severe diabetes mel1itus
Blood group incompatibilities
More than 4 :
Placental calcium deposition is a physiologic process
Found along the basal plate, in the intraplacental septa,
and in collections of fibrin in the intervillous and
Exponential increase in placental calcification with
increasing gestational age; more than 50% of placentas
contain some degree of calcification after 33 weeks.
Placental calcification is more common in women of
CLASSIFICATION OF PLACENTAL
EVALUATION - MRI
During the second trimester, most patients can tolerate
However, in the third trimester, lateral decubitus imaging
may be required
Avoid the risk of impaired systemic venous return caused
by uterine compression of the maternal inferior vena cava.
Imaging late in the third trimester can be challenging,
1. Positioning the patient
2. Placenta is heterogeneous
3. Myometrium thinner and more stretched
When evaluating the patient for placenta percreta,
the bladder should be mildly distended.
Completely collapsed bladder - Anatomic
landmarks difficult to identify
Full Bladder - exclusion of Bladder-wall invasion
difficult when closely apposed to the uterus.
No other patient preparation is typically required.
EVALUATION - MRI
Between 19 and 23 weeks:
homogeneous on T2
Between 24 and 31 weeks:
the placenta becomes slightly
conspicuous septae appear
between placental lobules,
leading to increased heterogeneity
with increasing gestational age.
The normal myometrium -
trilayered appearance on
The middle layer is a
layer, with thinner low
signal-intensity layers on
Failure of villous regression results in abnormalities
of placental shape.
A more common result of failure of villous
regression is the succenturiate (accessory) lobe,
which is present in up to 8% of patients
Recognition of succenturiate lobes is important
because they may result in complications such as
placenta previa, vasa praevia, and retained placenta
The membranes of
chorionic leave, instead
of attaching to margin of
placental disc, insert
more towards centre of
of placenta and fetal
membranes, results in
chorionic plate being
smaller than basal plate
Placenta membranacea is a rare anomaly in which
almost all the chorion is diffusely covered by villi.
A variant of this condition occurs when aberrant
villous atrophy results in a ring-shaped (annular)
Both entities are associated with recurrent
Transient changes in the appearance of
the retroplacental myometrium and
decidua are seen with contractions,
which occur throughout pregnancy
and are imperceptible to the mother.
These are most commonly seen in the
latter part of the first trimester and the
early part of the second trimester
Contractions are a source of
considerable confusion because they
often mimic retroplacental myomas
Well circumscribed and
Diagnosis easily confirmed if
multiple myomas are present.
Large myomas may have a
complex echotexture as a
result of degeneration and/or
May increase or decrease in
size during the course of the
"lakes" are not uncommon and may
At delivery, these correlate with
blood-filled spaces that presumably
represent a stage in the evolution of
either perivillous fibrin deposition
or intervillous thromboses.
SITE : PLACENTA PREVIA
Predisposing factors for placenta previa
Advanced maternal age Multiparity Prior
cesarean section Uterine curettage Maternal
Distinguish placenta accreta from increta and
increta from percreta - challenge, unless there is
direct invasion of adjacent organs.
Abnormal placental attachment to the myometrium
may be complicated by postpartum hemorrhage
and/or retained products of conception when the
placenta fails to cleanly separate from the uterus at
the time of delivery
MRI – highly accurate
Premature separation of placenta from the
Secondary to hemmorrhage into decidua basalis
20 wks to birth
If >60 ml blood
loss chances of
fetal demise more
Diffuse placental thickness
Rounded placental edge
Separation of placental edge
Preplacental or subamniotic mass
Blood in the fetal stomach
An enlarged uterus containing
material with multiple anechoic
vesicles of varying sizes, in the
absence of a fetus, is seen with
complete hydatidiform mole
The vesicles represent dilated,
hydropic villi that enlarge with
advancing gestational age; no
normal placental tissue is found.
Moles are believed to result
from the abnormal fertilization
of an empty ovum by a single
sperm with a duplicated
haploid genome (46,XX
karyotype) or, less commonly,
A coexistent fetus may occur
along with a mole in the case of
a twin pregnancy with one
An enlarged placenta with multiple
anechoic lesions - Partial mole
Normal villi interspersed with
hydropic villi; the fetus - abnormal.
Most partial moles are triploid (69
If they do not abort in the first
trimester frequently cause symptoms
of preeclampsia at about 18 weeks.
Can follow commonly after normal
Arises from intermediate
Rarest and most fatal
B – HCG not significant
Pt usually presents as focal
hypervascularity and low
impedance and av shunting
Floris color mosaic pattern
HIGH SYSTOLIC – LOW
PSV > 50/cm AND RI <0.5
PSV <50 cm/s and RI 0.7
The umbilical cord inserts into the fetal (chorio-
amniotic) membranes outside the placental margin
and then travels within the membranes to the
placenta (between the amnion and the chorion).
Remodelling of the placenta as a response to factors
that affect distribution of uterine blood flow (a
process known as trophotropism).
A marginal cord insertion may evolve into a
velamentous cord insertion as the pregnancy
The placenta should be evaluated, not only as a
necessary organ for fetal growth the development, but
also as a potential source of fetal disease and/or
USG is the modality of choice
Patients with suspected accreta spectrum should
undergo MR evaluation
Patients with undiagnosed bleeding may undergo MR
to rule out abruption