Placenta, Umbilical Cord, and Amniotic Flashcards
*What is the normal thickness of the placenta?
- At 12 weeks, 1.5 - 2 cm
- throughout 2nd and 3rd trimesters, 2-4cm
Possible causes of a thin placenta (placentomalacia)
- diabetes mellitus (long standing)
- IUGR
- placental insufficiency
- polyhydramnios
- preeclampsia
- small-for-dates fetus
Possible causes of a thick placenta (placentamegaly)
- diabetes mellitus
- maternal anemia
- infection
- fetal hydrops
- Rh isoimmunization
- multiple gestation
What is Placental Insufficiency (Uteroplacental Vascular Insufficiency)?
- early placental aging w/ grade 3 placenta late 2nd or early 3rd trimester
- placenta is unable to deliver an adequate supplly of nutrients and oxygen to the fetus and thus cannot fully support the developing baby
- occurs when placenta either doesn’t develop properly or b/c it has been damaged
- can result in IUGR
Causes of placental insufficiency
- diabetes
- post-term pregnancy
- preeclampsia (HTN, Proteinuria, Edema)
- smoking
- alcohol consumption
- drugs/alcohol abuse
What are the Placental Variants?
- Circumvallate Placenta
- Succenturiate lobe
- A bilobed placenta( bipartite placenta)
- Venous lakes (maternal lakes/placental lakes)
What is a circumvallate placenta?
- *a condition in which the chorionic plate is smaller than the basal plate
- is characterized by a loose, redundant ring of chorionic membrane encircling its fetal
- may be predisposed to early separation from the uterine wall and is associated with antepartum bleeding, IUGR, fetal anomalies, placental abruption, and perinatal death
What is succenturiate lobe?
-an accessory lobe of the placenta located away from the main placental body
What is a bilobed placenta (bipartite placenta)?
-a placenta that divided into 2 approximately equal sized lobes
What is venous lakes?
- also known as maternal/placental lakes
- pools of maternal blood within the placental substance
- they will appear as anechoic or hypoechoic areas, and may contain swirling blood. These are of little clinical significance.
What is Placenta Previa?
- *implantation with complete or partial covering of the internal os
- early in pregnancy, the placenta is less localized and often cover the internal os
- as the placenta localized, it usually migrates away from the os
- due to the growth of the uterus, the placenta has the potential to shift away from the cervix with advancing gestation
- even if the placental margin covers the os at 15-17wks, it is likely to migrate away later as the LUS elongates
*When should a patient be evaluated for placenta previa?
-*after 20 wks w/ an empty maternal bladder using a transabdominal approach
When does placenta previa require a c-section?
- when the placenta is visualized 2cm or less from the internal os near term
What are the subtypes of placenta previa
- complete (total) previa: placenta covers the internal os completely
- partial previa: placenta partially covers the internal os
- marginal previa: placenta encroaches on the internal os but does not cover it
- low-lying previa: placental edge extends to within 2cm of the internal os
When is low-lying previa commonly observed?
during 1st and early 2nd trimester
Which previa are often difficult to distinguish sonographically?
marginal and partial placenta previa
What are the causes of false- positive placenta previa?
- Focal myometrial contractions that occur in the LUS
- Overdistended urinary bladder may compress the LUS creating the appearance of previa where is does not exist
*What is a common cause of painless vaginal bleeding in the 2nd and 3rd trimester?
*placenta previa
Placenta previa is more common in women with:
-a history of multiparity, advanced maternal age, previous abortion, and prior c-section
Which scanning is extremely beneficial, esp. with advanced gestation when fetal head or parts obscure the internal os?
Translabial or transperineal
What is the preferred method of delivery for placenta previa and why?
-b/c both the pt and fetus have an increased risk of death
*What is Vasa Previa?
- *when the velamentously inserted cord vessels precede the fetal presenting part and are resting over the internal os of the cervix
- the body of the placenta is away from the os, but the membranes and cord vessels cover the internal os
- these vessels are prone to rupture as the cervix dilates
*What is vasa previa often associated with?
-*velamentous cord insertion
*What is placental abruption (abruptio placentae)?
-it is the premature separation of the normally implanted placenta from the uterine wall before the birth of the fetus, thus causing hemorrhage
What region should the sonographer be concentrating on when assessing for placental abruption?
-*retroplacental space/complex
What is the Retroplacental Complex (RPC)?
- the region behind the placenta and is composed of decidua basalis and portions of myometrium including the maternal veins which drain the placenta
- visualized post 20 wks of gestation
- seen as an echo-poor, subplacental region with linear horizontal echoes representing venous channels
- Doppler flow is noted within the vascular channels
How may the placental abruption be present?
-concealed abruption, partial abruption, marginal abruption, or be defined by its location
What maternal conditions are linked to development of placental abruption?
- hypertension
- preeclampsia
- cocaine use
- cigarette smoking
- poor nutrition
- trauma
What is concealed/complete abruption?
- the hemorrhage is confined to the uterine cavity located between the placenta and the myometrium
- is an emergent situation, leaving the fetus w/o oxygen & nutrients and can cause heavy bleeding and pain in mother
- *is the most severe, often results in the development of a retroplacental hematoma
What is the most severe placental abruption and its result?
- concealed/complete abruption
- can result in development of retroplacental hematoma
What is a partial abruption?
- often results in only a few cm’s of separation
- detachment is usually not severe
- if no blood remains concealed in the retroplacental space, sonographic diagnosis is not possible
What is marginal abruption?
- often referred to as subchorionic hemorrhage
- *lies at the edge of the placenta and is the most common placental hemorrhage identified with sonography
What is the most common placental hemorrhage identified with sonography?
-marginal abruption (subchorionic hemorrhage)
Chronic retroplacental hematoma
- can be identified either between the placenta and myometrium or under the chorionic membrane
- the persistence of unresolved blood clot in the retroplacental space is the result of a small placental abruption
What are the classic signs and symptoms of placental abruption?
- vaginal bleeding
- abdominal & back pain
- uterine tenderness
- rapid uterine contractions, often coming one right after another
How serious is placental abruption?
-is an urgent situation that can lead to fetal death from hypoxia and possibly the death of the mother
How does the amount of bleeding relate to placental abruption?
-the amount of vaginal bleeding can vary greatly, and doesn’t necessarily correspond to how much of the placenta has separated from the inner wall of the uterus
Is it possible to have a severe placental abruption and no visible bleeding?
-*YES, if the blood becomes trapped inside the uterus between the placenta and uterine wall
*What is placenta accreta, [increta, pecreta]?
- *abnormal implantation of placental tissue (chorionic villi) into the uterus beyond the endometrial lining OR abnormal adherence of the placenta to the myometrium in an area where the decidua is either absent or minimal
- placenta may attach to a uterine scar following a previous c-section and/or after uterine surgery. This explains association b/w anterior placenta previa and placenta accreta
What happens as a result of placenta accreta?
-abnormal adherence causes the placenta to not detach at birth, therefore an emergency hysterectomy may be warranted
What are the 3 terms associated with abnormal adherence of the placenta?
- placenta accreta
- placenta increta
- placenta percreta
Placenta accreta
- the chorionic villi growth invades the superficial layer of the myometrium, disrupting the normal uteroplacental vessels and myometrial border (RPC) causing loss of normal hypoechoic interface b/w the myometrium and placenta
- invades less than 50% of the way through the myometrium
Placenta increta
invasion of the placenta, loss of normal hypoechoic interface b/w the placenta and myometrium with invasion of the myometrium
-invades more than 50% of the way through the myometrium
Placenta percreta
-penetration of the placenta (the chorionic villi of the placenta encroach through the myometrial and serosal layer of the uterus into the adjacent maternal urinary bladder or pelvic structures causing loss of normal hypoechoic interface b/w the placenta and myometrium
What are the sonographic findings of placenta accrete (etc)?
- loss of the normal hypoechic interface (loss of definition border) b/w the placenta and myometrium
- thin myometrium posterior to the placenta
- placenta previa (frequent associated finding)
What is placental chorioangioma?
- benign vascular tumor of the placenta
- *most common tumor of the placenta
- approx. incidence is 1% of all pregnancies
- they’re usually asymptomatic and incidental finding, however large ones have been proven to have adverse effects on both the mother and fetus
*What is the most common tumor of the placenta?
-*placental chorioangioma
How do placental chorioangiomas look sonographically?
-solid hypoechoic or hyperechoic mass within the placenta
What is the normal umbilical cord anatomy?
two arteries and one vein surrounded by Wharton’s jelly and covered by amnion
What is Wharton’s jelly?
- surrounds vessels in cord for protection
- act as a cushion and a lubricant to allow the vessels to move and bend easily
- excessive amounts can cause the cord to appear thickened
*What is the most common abnormality of the umbilical cord
single artery umbilical cord
What is the typical measurement of a single umbilical artery?
-greater than 4mm and appears similar in size to the adjacent umbilical vein
What can a two vessel cord be associated with?
- GU anomalies
- CNS anomalies
- omphalocele
- cardiac anomalies
- Trisomy 13 & 18
- multifetal pregnancies
- IUGR
Where is cord insertion best evaluated?
transverse view of the abdomen at the level between the stomach and the bladder
What are abnormal cord insertion sites?
- Marginal cord insertion: at the edge of the placenta (a battledore placenta)
- Velamentous cord insertion: denotes the insertion of the umbilical cord into the membranes beyond the placental edge. often seen in association w/ vasa previa
Umbilical Cord Knot
- a cord knot
- Wharton’s jelly provides cushioning around the blood vessels and protects them even if cord gets knotted
- fetal prognosis depends on how tight the knot is
*What is a nuchal cord?
- *2 or more complete loops of umbilical cord around the fetal neck
- this can be a significant finding during the late 3rd trimester or in cases of oligohydramnios
- can be confirmed with color doppler
What are the types of umbilical cord cysts?
- Allantoic
- Omphalomesenteric
- —usually cause no related complications if blood flow unaffected
What is an Allantoic cyst?
-persistent urachus forms cystic structure within cord, usually close to the fetus abdomen and have been seen in connection with omphalocele and aneuploidy
What is an Omphalomesenteric cyst?
-persistent omphalomesenteric duct forms cystic structure within the cord.
What are the sonographic findings of umbilical cord cysts?
- cystic mass within the umbilical cord
- most often noted close to the fetal abdomen
Umbilical varix
- focal dilated segment of the umbilical
- differentiated from umbilical cyst w/ color doppler
- flow is seen within the varix, not within a cyst
*How is fetal well-being evaluated using PW doppler of umbilical cord?
*by measuring the systolic/diastolic ration (S/D ratio)
What does the S/D ratio assess?
the vascular resistance in the placenta by taking a sample of the umbilical artery
*What is normal arterial flow?
*low resistance with good diastolic flow
Where should umbilical cord Doppler by performed?
anywhere along the length of the cord
*What normally happens to the S/D ratio wit advancing gestation?
*it will decrease
When is umbilical cord doppler usually used and indicated?
-may be used in 3rd trimester and is indicated in scenarios where there is increased risk of fetal growth restriction or poor perinatal outcome
What happens with increased resistance?
-will cause decreased diastolic flow which indicates increase resistance to flow in the fetus
What does a higher S/D ratio mean?
the greater the difference between the systolic and diastolic velocities
What is an elevated S/D ratio associated with?
increased placental resistance and an increase in the risk of perinatal mortality and morbidity
What is absence or reversal of diastolic flow in the umbilical artery considered?
-it is irregular and associated with an increase incidence of IUGR and oligohydramnios
What fetal malformations are associated with polyhydramnios?
- cardiac and/or chest abnormalities
- chromosomal abnormalities
- duodenal atresia
- esophageal atresia
- gastroschisis
- neural tube defects
- omphalocele
- Rh incompatibility
- twin-twin transfusion syndrome
What fetal malformations are associated with oligohydramnios?
-bilateral multicystic dysplastic kidney disease
-bilateral renal agenesis
infantile polycystic kidney disease
-IUGR
-posterior urethral valves
-premature rupture of membranes (PROM)
What is an important sonographic landmark in the diagnosis of placental abruption?
-the retroplacental complex of blood vessels
