Normal placental anatomy and morphology.
Normal variants of placenta.
Pathologic conditions of the placenta.
• Placental causes of hemorrhage.
• Gestational trophoblastic disease.
• Nontrophoblastic placental tumors.
• Cystic lesions.
Placenta is responsible for the nutritive, respiratory,
and excretory functions of the fetus.
Color and power Doppler techniques permit direct
visualization of placental vascularity, allowing
assessment of both the uteroplacental and
Sonography remains the imaging modality of choice
for evaluation of the placenta.
It is uniformly of intermediate echogenicity, with a
deep hypoechoic band at the interface between the
myometrium and basilar decidual layer.
The overall appearance of the placenta changes during
the course of pregnancy, with the progressive
development of calcifications.
Early maturation of the placenta increases the risk of
adverse fetal outcomes.
It is expressed in terms of thickness in the mid portion of
the organ and should be between 2 and 4 cm.
Placental thinning (<2 cm): Has been described in systemic
vascular and hematologic diseases that result in
Thicker placentas (>4 cm) are seen in:
Can be simulated by myometrial contractions .
Typically, the placenta is located along the anterior or
posterior uterine wall, extending onto the lateral walls.
Although usually discoid, the placenta can be variable
Variant placental shapes include:
Succenturiate lobe : Is an additional lobule separate
from the main bulk of the placenta.
SIGNIFICANCE: Rupture of vessels connecting the two
components, retention of the accessory lobe with
resultant postpartum hemorrhage
Bilobed placenta: Placenta with two relatively even
sized lobes connected by a thin bridge of placental
Circumvallet placenta: Chorionic plate smaller than
the basal plate with associated rolled placental edges.
SIGNIFICANCE: Placental abruption and hemorrhage.
Placenta membranacea : Thin membranous structure
circumferentially occupying the entire periphery of the
SIGNIFICANCE : Placenta previa, as a portion of the
placenta completely covers the internal cervical os
The umbilical cord typically inserts centrally, but eccentric
and velamentous (outside the placental margin) insertions
Eccentric insertions are cord insertions that are <1 cm from
the placental edge.
Velamentous insertion: here the umbilical cord inserts on
the chorioamniotic membranes rather than on the
This membranous insertion results in a variable segment of
the umbilical vessels running between the amnion and the
chorion, unprotected by Wharton jelly.
Importance of evaluation of placenta in twin gestation
lies in deciding the chorionicity.
The increase in perinatal complications is correlated
with placental chorionicity, with a higher rate of
morbidity and mortality seen in monochorionic than
Monochorionic twins are always monozygotic whereas
dichorionic twins can be mono or dizygotic.
US is capable of demonstrating chorionicity with a
high degree of specificity and sensitivity.
Clear distinction of two placentas may be difficult,
particularly if the two sites of blastocyst implantation
In these cases, the twin peak sign and T sign can be
helpful in defining chorionicity.
The twin peak sign is a triangular projection of
placental tissue extending up the inter-twin
membrane (opposed amnions) in dichorionic-
diamniotic twinning. It is visible in the late first and
early second trimester. Thickness of membrane : >=2
Twin peak sign in dichorionic-diamniotic twin gestations.
The T sign is a 90° intersection of the intertwin
membrane with the single placenta in a
monochorionic-diamniotic gestation. Thickness of
membrane : approx. 1 mm.
T sign in a monochorionic-diamniotic twin gestation
• Placental causes of hemorrhage.
• Pathological conditions towards maternal side and
within the placenta.
• Gestational trophoblastic disease.
• Nontrophoblastic placental tumors.
Antepartum hemorrhage remains an important cause
of maternal and fetal morbidity and mortality.
Placenta previa and placental abruption account for
more than one half of cases of antepartum
Another condition called vasa previa is also associated
with antepartum hemorrhage.
It represents premature separation of the placenta
from the uterine wall.
Although rare, third-trimester abruption is associated
with an increased risk of preterm delivery and fetal
US is frequently performed to confirm the presence of
abruption and assess the extent of subchorionic or
The presence of blood in large enough volumes to be
visible sonographically indicates retained hemorrhage
that may remain symptomatic.
False-negative results can occur when blood dissects
out from beneath the placenta and drains through the
Within the Placenta Maternal side
Subamniotic 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. Subamniotic bleeding is rare.
Subchorionic bleeding dissects chorion and endometrium; when such
bleeding involves margin of placenta, it is called marginal subchorionic
Retroplacental bleeding is found behind placenta.
Placental hematomas appear as well-circumscribed
masses with echogenicity that varies according to
Acute : Hypoechoic or anechoic.
Subacute : Heterogeneously echogenic.
Chronic : Anechoic.
Doppler interrogation should reveal absence of
internal blood flow; this finding allows differentiation
of hematomas from other placental masses
Placenta previa refers to abnormal implantation of the
placenta in the lower uterine segment, overlying or
near the internal cervical os.
Normally, the lower placental edge should be at least 2
cm from the margin of the internal cervical os.
The relationship of the placenta to the internal os
changes throughout the course of pregnancy as the
The diagnosis of placenta previa should not be made
before 15 weeks gestation, and low-lying or marginal
placental positioning should be re-evaluated later in
gestation to confirm placental position before delivery.
Placenta previa can be subdivided according to the
position of the placenta relative to the internal cervical
Lower placental margin is within 2 cm of the
internal cervical OS.
Marginal previa Placenta extends to the edge of the internal OS
but does not cover it.
Complete previa Placenta covers the internal OS.
Central previa Central placenta is implanted directly over the
It refers to the presence of abnormal fetal vessels
within the amniotic membranes that cross the internal
These vessels are unsupported by Wharton jelly or
placental tissue and are at risk of rupture.
Rupture of these vessels can lead to catastrophic fetal
In cases of vasa previa, the abnormal vessels either
A velamentous cord insertion with the main body of the
Connect portions of a bilobed placenta
Placenta with a succenturiate lobe.
Given this association, vasa previa needs to be excluded in
patients with variant placental morphology.
The diagnosis of vasa previa is made with Doppler US,
which demonstrates vascular flow within vessels
overlying the internal cervical OS.
As with placenta previa, patients with vasa previa
diagnosed in the second trimester should be re-
evaluated later in gestation. The vasa previa can
resolve as the uterus enlarges and the relationship of
the placenta to the internal os changes.
During the process of placental development and
implantation, a defect in the normal decidua basalis
from prior surgery or instrumentation allows
abnormal adherence or penetration of the chorionic
villi to or into the uterine wall.
This abnormal adherence of the placenta to the uterus
can result in catastrophic intrapartum hemorrhage at
the time of placental delivery, often necessitating
Placenta accreta : chorionic villi attach to myometrium
(more than 1/3rd ), rather than being restricted within
the decidua basalis.
Placenta Increta : Chrionoc villi invade into the entire
Placenta Percreta : Chorionic villi invade through the
myometrium upto serosa.
Sonographic features of placenta accreta and increta
loss of the normal retroplacental clear space
prominent placental lacunae
increased vascularity at the interface of the uterus and
Of these various sonographic features, the presence of
prominent placental lakes has the highest positive
predictive value. Lacunae are characterized by ill-
defined margins, irregular shape, and turbulent flow.
The vast majority of hypoechoic foci in the placenta
Intervillous space thrombi
The term placental lakes may also refer to intervillous
vascular spaces that appear hypo to anechoic and
demonstrate low-velocity laminar flow on colour Doppler
Intervillous space thrombi form due to focal fetal
hemorrhages that rapidly thrombose in the maternal
blood pool of the intervillous space.
Most intervillous space thrombi are visible as
hypoechoic foci smaller than 1–2 cm and are of limited
Lesions larger than 3 cm may be indicative of
underlying placental disease
Placental infarction : can occur focally or throughout
the placenta. Thought to have vascular etiology.
They appear as cystic lesions with echogenic rim
within the placenta, without internal vascularity.
True placental cysts occur on the fetal surface of the
placenta, typically near the cord insertion.
The majority are simple with internal echogenicity
identical to that of amniotic fluid.
The common feature for this group of disorders is the
abnormal proliferation of trophoblastic tissue with
excessive production of β–human chorionic
It encompasses :
hydatidiform moles (most common).
First-trimester bleeding is one of the most common
clinical presentations for this group of disorders.
Other clinical signs and symptoms include :
rapid uterine enlargement
excessive uterine size for gestational age
preeclampsia that occurs in the early second trimester.
It is classified into two major types :
Complete (more common)
Complete moles result from fertilization of an empty
ovum with subsequent duplication of the paternal
This chromosomal anomaly causes early loss of the
embryo and proliferation of the trophoblastic tissue.
At US, complete moles appear as a heterogeneous
echogenic endometrial mass with multiple variable-
sized small anechoic cysts, giving the appearance of a
There is no identifiable fetal tissue.
At color Doppler interrogation, increased vascularity
with low resistance waveforms can be identified in the
spiral arteries of the uterus.
Partial hydatidiform moles result from fertilization of
a normal ovum by two sperm.
At sonography, partial moles appear similar to
complete moles but are differentiated by the presence
of fetal tissue.
Invasive Moles : Invasive moles represent deep growth
of the abnormal tissue into and beyond the
myometrium, sometimes with penetration into the
peritoneum and parametrium.
They need to differentiated from Choriocarcinoma.
It is the malignant trophoblastic disease of placenta.
Invasive moles and chroriocarcinomas are largely
indistinguishable at imaging.
At sonography, both appear as heterogeneous,
echogenic, hypervascular masses.
Choriocarcinoma Invasive moles
Areas of intralesion necrosis and
hemorrhage can be seen within
Capable of metastasizing, frequently
manifesting with lung and pelvic
Non metastasizing neoplasms
Nontrophoblastic placental tumors are quite rare.
They are mainly :
Chorioangiomas (less than 1% of pregnancies)
Placental teratomas (extremely rare)
Placental teratomas are similar in appearance to
chorioangiomas, but are differentiated by the presence
Chorioangiomas are the most common benign
vascular tumour of placental origin.
They are essentially hemangiomas of the fetal portion
of the placenta, supplied by the fetal circulation.
Although the vast majority are small and of no clinical
significance, large (>5 cm) or multiple lesions (so-
called chorioangiomatosis) stress the fetal circulation
and can be associated with complications such as
hydrops, thrombocytopenia, intrauterine growth
retardation, and an overall increase in antepartum
Most of them are incidentally identified.
These lesions appear :
well-circumscribed, rounded, hypoechoic masses
protruding from the fetal side of the placenta.
Usually contain anechoic cystic areas.
And some heterogenous areas caused by internal
hemorrhage / degeneration.
Can be pedunculated.
Most are located near the cord insertion, and Doppler
imaging reveals low resistance pulsatile flow wihtin
the anechoic areas which represents a large feeding