Podcast
Questions and Answers
What is a primary concern associated with a prominent anterior retroplacental complex (RPC)?
What is a primary concern associated with a prominent anterior retroplacental complex (RPC)?
What is the primary utility of real-time visualization of blood flow in the retroplacental complex (RPC)?
What is the primary utility of real-time visualization of blood flow in the retroplacental complex (RPC)?
In which placental location are large venous channels most commonly visualized, due to the effects of gravity-induced pressure?
In which placental location are large venous channels most commonly visualized, due to the effects of gravity-induced pressure?
According to the provided information, what is the primary use for placental grading?
According to the provided information, what is the primary use for placental grading?
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A placenta with scattered calcifications and a slightly contoured chorionic surface is most likely classified as which grade?
A placenta with scattered calcifications and a slightly contoured chorionic surface is most likely classified as which grade?
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Which type of placental variant is characterized by fetal membranes that 'double back' on the fetal side, forming a small central ring?
Which type of placental variant is characterized by fetal membranes that 'double back' on the fetal side, forming a small central ring?
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What potential complication is associated with a circumvallate placenta due to the way the membranes are formed?
What potential complication is associated with a circumvallate placenta due to the way the membranes are formed?
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What is a distinguishing feature of a circumvallate placenta observed after delivery?
What is a distinguishing feature of a circumvallate placenta observed after delivery?
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Which of the following best describes a circummarginate placenta?
Which of the following best describes a circummarginate placenta?
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What is a succenturiate placenta?
What is a succenturiate placenta?
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Which of the following is a characteristic finding of a circumvallate placenta on ultrasound?
Which of the following is a characteristic finding of a circumvallate placenta on ultrasound?
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Placentomegaly is defined by an anterior-posterior (AP) placental measurement greater than:
Placentomegaly is defined by an anterior-posterior (AP) placental measurement greater than:
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Which of the following would NOT typically cause increased placental thickness?
Which of the following would NOT typically cause increased placental thickness?
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A decreased placental thickness, measuring less than 1.5 cm AP, can be caused by all of the following EXCEPT:
A decreased placental thickness, measuring less than 1.5 cm AP, can be caused by all of the following EXCEPT:
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Which of the following is a characteristic symptom of placenta previa?
Which of the following is a characteristic symptom of placenta previa?
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What is the vertical axis used to divide the uterus into four quadrants?
What is the vertical axis used to divide the uterus into four quadrants?
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A woman at 32 weeks gestation has an AFI of 28cm. What would this be considered?
A woman at 32 weeks gestation has an AFI of 28cm. What would this be considered?
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A bipartite placenta is best described as which of the following?
A bipartite placenta is best described as which of the following?
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What technique for amniotic fluid measurement is considered more favorable after 22 weeks gestation?
What technique for amniotic fluid measurement is considered more favorable after 22 weeks gestation?
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According to the SAFE trial, what was the primary finding regarding the AFI technique?
According to the SAFE trial, what was the primary finding regarding the AFI technique?
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What is the normal range for AFI?
What is the normal range for AFI?
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Which of the following best describes a complete placenta previa?
Which of the following best describes a complete placenta previa?
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What is the primary difference between a concealed and external placental abruption?
What is the primary difference between a concealed and external placental abruption?
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Which of the following is NOT typically considered a predisposing factor for placental abruption?
Which of the following is NOT typically considered a predisposing factor for placental abruption?
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A low-lying placenta is defined as:
A low-lying placenta is defined as:
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Sonographically, what is a common finding associated with placental abruption?
Sonographically, what is a common finding associated with placental abruption?
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Which of the following is a predisposing factor for abnormal placental adherence?
Which of the following is a predisposing factor for abnormal placental adherence?
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A patient presents with painless vaginal bleeding. Which of the following would be the LEAST likely cause?
A patient presents with painless vaginal bleeding. Which of the following would be the LEAST likely cause?
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What sonographic feature might be seen with a placental abruption?
What sonographic feature might be seen with a placental abruption?
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What type of tumor is a chorioangioma?
What type of tumor is a chorioangioma?
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What is a possible complication associated with a large chorioangioma?
What is a possible complication associated with a large chorioangioma?
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What is the average length of the umbilical cord at term?
What is the average length of the umbilical cord at term?
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What is the main function of the umbilical vein?
What is the main function of the umbilical vein?
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What does the presence of an absent blood flow on Doppler assessment generally indicate in relation to the placenta?
What does the presence of an absent blood flow on Doppler assessment generally indicate in relation to the placenta?
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Which structure forms the definitive umbilical vessels?
Which structure forms the definitive umbilical vessels?
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Which imaging technique is important for visualizing the umbilical cord?
Which imaging technique is important for visualizing the umbilical cord?
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What common anatomical structure surrounds the umbilical vessels within the cord?
What common anatomical structure surrounds the umbilical vessels within the cord?
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What condition is characterized by the complete absence of amniotic fluid?
What condition is characterized by the complete absence of amniotic fluid?
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Which of the following is NOT associated with oligohydramnios?
Which of the following is NOT associated with oligohydramnios?
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What is the main purpose of amniocentesis performed in the late second and third trimesters?
What is the main purpose of amniocentesis performed in the late second and third trimesters?
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A ratio greater than 2:1 in the lecithin/sphingomyelin (LS) test indicates what regarding respiratory distress syndrome?
A ratio greater than 2:1 in the lecithin/sphingomyelin (LS) test indicates what regarding respiratory distress syndrome?
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Which fetal condition can be caused by fetal hydrops?
Which fetal condition can be caused by fetal hydrops?
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What is the significance of differentiating between various intrauterine membranes and amniotic bands?
What is the significance of differentiating between various intrauterine membranes and amniotic bands?
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Which maternal condition can be a cause of polyhydramnios?
Which maternal condition can be a cause of polyhydramnios?
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What is the primary method used to diagnose chromosomal conditions around 16 weeks of gestation?
What is the primary method used to diagnose chromosomal conditions around 16 weeks of gestation?
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Study Notes
The Placenta and Umbilical Cord
- Accurate assessment of the placenta and umbilical cord is an important part of routine obstetric sonographic examinations.
- Placental evaluation usually includes assessment of size, shape, consistency, and location.
- Umbilical cord evaluation by ultrasound should confirm the number of vessels, document length, and appearance of the cord, and visualize the insertion points.
Normal Placenta
- A discoid organ that typically weighs 500-600 grams at delivery.
- Usually 2-4 cm in anteroposterior (AP) dimension.
- The maternal surface is irregular and divided into cotyledons.
Why Care About the Placenta?
- Placental pathology or abnormal development can lead to complications during pregnancy.
- Sonographers use tools to evaluate placental morphology, localization, and feto-placental hemodynamics.
- Placental pathology often requires further investigation to minimize fetal risks.
Development of the Placenta
- Composed of maternal and fetal portions:
- Maternal portion arises from the endometrium.
- Fetal portion arises from the chorionic sac.
- The functional layer of the endometrium in a pregnant woman is called the decidua.
- Decidua basalis is the deeper portion and becomes the maternal side of the placenta.
- Decidua capsularis overlies the embryo.
- Decidua parietalis/vera encompasses the remaining decidua.
The Placenta
- Attachment to the uterine wall can occur anywhere within the uterine cavity.
- Fetal side is a fused layer of amnion and chorion (chorionic plate) with fetal vessels underneath.
- Maternal side has about 20 functional lobes (cotyledons) composed of maternal sinusoids and chorionic villous structures.
- Sonographically, the placenta is relatively homogeneous, but may show calcification and anechoic spaces (lacunae) in later pregnancy.
Placental Circulation
- Maternal and fetal circulations are separate.
- Oxygenated maternal blood is pumped through spiral arterioles and enters intervillous spaces (sinus) around the villi.
- Gas and nutrient exchange occurs across the villus walls.
- Oxygenated blood returns to the fetus by the umbilical vein.
- Deoxygenated fetal blood returns to the placenta by the umbilical arteries, circulating through capillaries in chorionic villi.
- Maternal blood volume increases during pregnancy to meet fetal needs. Many vascular channels in the placenta create a low-impedance system, at least until late in pregnancy.
Sonography of the Placenta
- By the fourth month, sonography can identify the placenta's final shape.
- Normal cord insertion is usually central, but can be eccentric (battledore or velamentous insertion).
- Thicker placental base usually means a thinner placenta.
- Placental length, volume, and thickness help correlate pregnancy outcomes.
- A placental thickness greater than 4 cm before 24 weeks is often abnormal.
- Transabdominal scanning with a curvilinear or linear transducer is used for evaluation.
- Endovaginal transducers allow for earlier visualization and are ideal for questionable cases of placenta previa.
- Transperineal ultrasounds are used in situations where endovaginal imaging is not possible.
A Full Bladder
- A full bladder enhances placental visualization in early and later pregnancy.
- A full bladder is crucial when considering a diagnosis of placenta previa.
- An empty bladder may hinder visualization of the cervix.
- Sonographers should encourage emptying of a portion of the bladder to prevent a false-positive diagnosis.
- A bladder is considered appropriately full when cervical length is between 3-5 cm.
Placental Texture
- Placental texture changes from an echogenic focal thickening—early pregnancy—to a homogeneous, granular texture later in the pregnancy.
- Intraplacental vascular spaces can be observed.
- Areas of varying echogenicity should be carefully documented.
- Increased AFP levels may correlate with larger vascular spaces.
The Retroplacental Complex
- The retroplacental complex is composed of the decidua basalis and portions of the myometrium.
- Deep hypoechoic area of 10-20mm is visible as early as 14 weeks.
- Proper identification is necessary.
- A prominent anterior retroplacental complex may lead to excessive bleeding during procedures.
Color Doppler image of the retroplacental vessels
Placental Grading
- Structural changes occur in the placenta as it ages.
- Placental grading, to determine gestational age, has poor correlation in practice.
- A grade II placenta in the second trimester or early third trimester could indicate placental insufficiency, especially with maternal complications.
Placental Variants
-
Extrachorial: Membranous chorion does not extend to the edge of the placenta. This might be associated with hemorrhage.
- Circumvallate: Fetal membranes fold back around the edge of the placenta.
- Circummarginate: Flat transition of membranes inserted at some distance from the placental edge.
Accessory Types of Placentas
- Succenturiate: Accessory cotyledons connected to the main placenta.
- Bipartite: Placenta divided into two lobes but united by vessels and membranes.
- Annular: Ring-shaped placenta.
Abnormal Placental Thickness
- Normally, the placenta is less than 5 mm in AP measurement.
- Thickening (placentomegaly) over 5 cm can have various causes.
- Gestational diabetes
- Rh isoimmunization
- Maternal infection
- Chorioangioma
- Multiple gestation
- Hydrops fetalis
- Sacrococcygeal teratoma
- Partial moles
- Chromosomal abnormalities
- Abruption (not necessarily thicker, only appears that way due to clot)
Placentomegaly & Fundal Placenta
- Fundal placenta refers to a placenta that is implanted near the fundus of the uterus.
Decreased Placental Thickness
- Placenta measures less than 1.5 cm in AP measurement.
- Pre-eclampsia, IUGR, intrauterine infections, and polyhydramnios are possible causes.
Abnormal Placental Location - Placenta Previa
- Placental tissue encroaches on the cervix.
- Caused by implantation of the blastocyst.
- Painless vaginal bleeding during the third trimester is a classic symptom.
- Best diagnosed sonographically in the third trimester due to placental migration.
Classification of Previa
- Complete/total/central previa: Placenta completely covers the cervix internal os.
- Partial previa: Partially covers the cervix internal os.
- Marginal previa: Encroaches on the cervix but does not cross it.
- Low-lying placenta: Placenta is within 2 cm of the cervix internal os.
Placental Abruption
- Premature separation of part or all of a normally implanted placenta from the myometrium
- Maternal hypertension, advanced maternal age, multiparity, and uterine leiomyoma are risk factors.
- Abdominal pain and vaginal bleeding are common symptoms
- May be concealed or external
Placental Abruption - Sonographic Findings
- Elevation of the placenta from the uterine wall
- Retroplacental fluid collection, varying in echogenicity (usually hypoechoic) is indicative of hemorrhage
- Could appear normal or thickened due to hemorrhage.
Abnormal Placental Adherence
- Rare condition resulting from defective decidual formation.
- Associated with placenta previa.
- Could result in uterine scarring.
- Types include, Accreta (chorionic villi in direct contact with the myometrium, but do not invade) , Increta (chorionic villi invade the myometrium), and Percreta (chorionic villi penetrate the myometrium).
Intraplacental Lesions - Placental Lakes
- Intraplacental lesions which are the presence of large pools of maternal venous blood are usually insignificant.
- They appear as anechoic/hypoechoic rounded areas within the placenta.
Intraplacental Lesions - More Infarcts
- Ischemic necrosis of placental villi occurs due to spiral artery obstruction. Usually found at the periphery of the placenta.
- Usually found in eclampsia or pre-eclampsia cases with may also be associated with intervillous thrombus and retroplacental hemorrhage .
- Appear as anechoic or hypoechoic areas in the placenta, and may not have a specific sonographic appearance.
- Absence of blood flow with color and spectral Doppler signals may be suggestive.
Chorioangioma
- Vascular tumor of the placental tissue occurring in approximately 1 in 5,000 pregnancies.
- Complications arise when larger than 5cm, and may be associated with polyhydramnios and fetal hydrops..
- Appearance is a solid, well-circumscribed placental mass, often near the cord insertion site.
Placenta Variations
- Descriptions of the different ways a placenta can develop.
Umbilical Cord
- Umbilical cord originates from the yolk sac stalk and omphalomesenteric duct by the 7th week.
- Contains 2 arteries and 1 vein enveloped in Wharton's Jelly, which is mucoid connective tissue.
- Blood vessels carry oxygenated blood to the fetus and deoxygenated blood away from the fetus.
- Average length and circumference are around 51.5-61cm and 3.8cm respectively.
Umbilical Cord
- Visualization best during late second/early third trimester due to amniotic fluid volume.
- Scan the entire cord to identify possible abnormalities.
- Changing maternal positions can shift fetal position to get better visualization of the cord.
- Three vessels should be noted.
Normal Sonographic Appearance
- In early pregnancy, the cord appears as short, linear echoes extending from the fetus to the placenta.
- As pregnancy progresses, transverse images show three distinct circles with the vein being the largest.
- Longitudinal images may show a "stack of coins" appearance from the various portions of the cord folded together.
- Arterial pulsations are observed within the umbilical arteries.
Abnormal Umbilical Cord
- Single Umbilical Artery (SUA): One umbilical artery instead of two; associated with other congenital anomalies.
- Umbilical Cord Cysts: Developmental and asymptomatic focal accumulations of Wharton's jelly that appear as cysts.
Nuchal Cord
- Cord wrapping around the fetal neck.
- Common in 20% of pregnancies.
- Rarely associated with important complications. Differentiation between cord draping across the back of the neck vs. wrapped around the neck is essential.
Cord Prolapse
- Cord protruding through the cervix or adjacent to fetal presenting part.
- Considered an emergent situation.
Vasa Previa
- Fetal vessels cross over the cervix.
- Associated with velamentous insertion.
- Presence of fetal vessels crossing over the internal cervical os is an emergency situation.
Umbilical Vein Thrombosis
- Possible causes include torsion, knotting, or compression of the cord or after intrauterine transfusion or fetal blood sampling.
- Increased echogenicity within the umbilical vein lumen, and absence of color and Doppler signals may be suggestive.
Umbilical Cord Knots
- Rare occurrence, often associated with monozygotic twins.
- Appears as multiple cord loops in one image scan.
Placental Cord Insertion Sites
- Normal: Central insertion
- Marginal/Battledore: Peripheral cord insertion at the edge of the placenta.
- Velamentous: Cord insertion into the membranes before entering the placenta, which can be associated with fetal anomalies.
Amniotic Fluid
- Produced by the fetal kidneys, tissues, skin, and membranes.
- Cushions the fetus.
- Regulates temperature and pressure.
- Enables fetal development of the lungs.
- A lack or excess of amniotic fluid can cause complications.
Fluid Estimation (AFI) and Single Deepest Pocket
- AFI: Sum of the largest vertical pocket measurements in four uterine quadrants.
- Single Deepest Pocket (SDP): Measures the largest vertical pocket alone.
- Guidelines for categorizing levels of amniotic fluid:
- Oligohydramnios (<5cm)
- Decreased fluid (5.1-8cm)
- Normal (8.1-25cm)
- Polyhydramnios (>25cm)
Oligohydramnios
- Abnormally decreased amniotic fluid volume.
- Associated with fetal demise, renal abnormalities, IUGR, and post-dates.
- Also associated with preeclampsia or eclampsia.
Anhydramnios
- Complete absence of amniotic fluid.
Polyhydramnios
- Abnormally increased amniotic fluid volume.
- Possible causes include maternal diabetes, Rh incompatibility, fetal CNS or GI anomalies, and facial clefts.
- Associated with fetal hydrops, twin-twin transfusion syndrome, sacrococcygeal teratoma, and skeletal dysplasia.
Amniocentesis
- Procedure to obtain amniotic fluid for analysis.
- Rate of complications is 0.5%.
- Performed in the late second or third trimester.
Fetal Membrane Abnormalities
- Various intrauterine membranes, septations, and bands are found.
- Chorioamniotic separation can occur due to intervention such as amniocentesis. Or it can be sporadic, without an obvious reason; and it is associated with chromosomal or developmental abnormalities
- Intrauterine synechiae are linear, and external to the amniotic sac, tissues that project into the amniotic cavity. They are usually an incidental finding. This is not associated with fetal anomalies.
- Amniotic Band Syndrome: Occurs due to rupture of the amnion without rupturing the chorion. This can cause malformations, amputations, constriction rings, and facial clefts.
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Description
Test your knowledge on key concepts in maternal-fetal medicine, focusing on placental conditions and imaging techniques. This quiz covers concerns with the retroplacental complex, placental grading, and variations. Assess your understanding of placental anatomy and complications.
