OB Exam 2 Flashcards
2nd & 3rd trimester extrafetal structures
- cervix
- placenta
- membranes
- uterine wall
- umbilical cord, including insertions
- amniotic fluid
*pay attention to baby’s position
When should you look for baby’s position?
look in each quadrant while examining extrafetal structures
Appearance of cervix on ultrasound
- closed, lengthy
- free of placental margins & blood vessels
- may require TV or transperineal imaging (TV unless PROM)
- cavity is outside of pregnancy
Measuring cervix
- > 3cm
- greater than 4cm = need to re-evaluate
- pitfalls: bladder distention; LUS contraction
Why does the cervix need to be free of placental margins and blood vessels?
- don’t want placenta covering internal os of cervix (placenta previa) b/c it will come out before baby
What is placenta previa?
when the placenta is covering the internal os of the cervix
What is basa previa?
when the cord tries to come out before baby
What technique should you use to see the baby’s head if the head is down on top of the cervix?
come from the side and under to push the baby’s head into view
Transperineal imaging of cervix
- cover transducer and place it btwn. labia
- imaging from feet to head
- look through vaginal canal to see where it connects to cervix
- push down some to see if cervix opens w/ pressure
- measure cervix
Transvaginal imaging of cervix
- don’t have to do TV into 2nd & 3rd trimester if you can see accurately in TA
- don’t push too hard on cervix b/c you might make it look abnormal
In TV imaging, where should you start your cervix measurement?
at the vaginal fornix
Pitfalls of cervix imaging
- bladder is flattening cervix out, making it measure longer (too long)
- get that area relaxed
Abnormalities in 2nd & 3rd trimester
- placenta previa
- shortening & funneling
- incompetent cervix
What is an incompetent cervix?
- weak cervix
- loosens up
- can cause some bleeding
Inside the placenta
- chorionic villi form lacunar networks
- groups of lacunar networks form cotyledons
What are lacunar networks?
- spiral arteries at the intervillous spaces of the placenta
- spaces allow for easy movement of nutrients coming in and out
What happens if there is too much pressure in the lacunar networks?
- placenta can’t function
- hydration helps ease pressure
- needs to have enough pressure to make things move but too much pressure is bad
What are cotyledons?
cluster of networks
Circulatory system of the placenta from outer uterus to pregnancy
- decidua basalis of uterus
- chorionic villi
- intervillous sinusoid
- chorionic plate
What is the chorionic plate?
layer of chorion and amnion located at the surface of the placenta next to the fluid
Describe the vessels of the placental circulatory system
- vessels come underneath/between chorion to baby (they do not touch amniotic fluid)
- umbilical chord is covered w/ a layer of amnion
- mom’s vessels do not directly communicate with baby’s vessels
- exchange happens in placental membrane
Describe the placenta at a microscopic level
placental membrane:
- capillary-like structure
- prevents ‘mixing of maternal/fetal blood
- protects fetus from potentially harmful agents
Describe the placenta sonographically
outside of the pregnancy:
- basal layer (decidua basalis, aka retroplacental complex)
- placental substance: cotyledons, chorionic villis
What are placenta lakes?
- intervillis spaces that have extra fluid in them
- unless adding extra pressure, not an issue
Locations of the placenta
- anterior/posterior/lateral
- fundal vs. cervical
- previa vs. low lying
Types of placenta previa
- complete previa: blocking cervix
- partial previa: to the side and partially blocking
- marginal previa: to the side, close, might be blocking
- low-lying previa: to the side, close, not blocking
What else should you look for when evaluating the placenta?
accessory placenta
How to determine the position of the placenta
- away from transducer is posterior
- close to transducer is anterior
By what weeks can you determine placental location?
confirm around 26-28 weeks b/c placenta can migrate due to expanding
Determining placenta maturity
- extremely subjective
- grading system: grades 0-3 (total of 4)
- should be grade 0 until 32 or 33 weeks
How can we show bloodflow between baby and placenta?
cord doppler
What can put the placenta at risk?
- smoking
- HTN
- diabetes
- poor nutrition/prenatal care
What does the placenta look like sonographically as it starts to mature?
- salt and pepper
- later on you see clusters forming
Normal placenta attachment
attached to uterine wall, posterior to basal layer
Placenta creta
- abnormal placenta attachment
Types of placenta creta
- acreta = adhered
- increta = invaded
- percreta = perforated
What is acreta?
- blood vessels of placenta attach to myometrium
- almost impossible to diagnose
- make sure placenta is not attached outside uterus
What is important to know when examining the placenta?
if the patient had a C-section
Can the patient deliver vaginally with an abnormal placenta attachment?
No, will need a C-section
What will an abnormal placenta attachment look like?
- bladder doesn’t have a wall separating it
- bladder appears to be touching placenta
- C-section scar may cause placenta to buldge & lie anteriorly
If the placenta is abnormal, what needs to be done after the C-section?
- leave placenta inside mom
- provide high dose of ectopic medication to save her life
- try to save bladder, cannot save uterus
Accessory lobes of placenta
- succenturiate
- chorionic villi started to develop, then stopped
- has to be diagnosed so doctors can get all of it out during birth
What are we evaluating for when we look at the amnion?
- continuity and intact
- amniotic bands
- amniotic sheets
What are amniotic bands?
- thin, free floating membrane that connects to the fetus
- can cause a rupture and adherence/entrapment to fetal parts
What are amniotic sheets/synechiae?
- ‘scar’ w/in uterine cavity that indents the pregnancy as it grows
- appears thicker as a result of double layer of amnion and chorion
What are the 2 types of membranes?
amnion and chorion
What are we evaluating when we look at the chorion?
attachment to placenta
Circumvallate
fold in the chorion that can cause the false appearance of a separate cavity
What are we evaluating when we look at the umbilical cord?
- vessel number: 1 vein, 2 arteries
- hypercoiling and hypocoiling
- placenta resisting bloodflow
- 2VC/SUA
- insertions
Vein within umbilical cord
- 1 vein
- larger vessel
- supplies fetus
- courses to liver (portal sinus) first
Arteries within umbilical cord
- 2 arteries
- smaller vessels
- returns de-O2 blood to placenta
- Doppler waveform changes as placenta changes
What covers the umbilical cord?
amnion and Wharton’s Jelly
Pitfall of looking for the umbilical cord
don’t confuse illiacs for cord
What insertions are we imaging with the umbilical
- placenta
- abdominal wall (AW)
Types of cord insertions
- central attachment: ideal
- marginal/battledore: increased risks
- velamentous: significant risks, off of edge
- vasa previa: dangerous
What is vasa previa?
- type of cord insertion (velamentous + previa)
- dangerous risks, such as hemorrhage
- off of edge & cervix is btwn.
- cord goes across cervix
Purpose of amniotic fluid
- shock absorber
- maintain temp.
- allow movement for fetal tone (exercise)
How do we measure amniotic fluid?
- using AFI > 28 weeks
- sum of 4 quadrant depths
- 10-20cm ideal (not a volume but an index)
- 5-25cm = ok
- <5cm = oligohydramnios (might go in and drain some)
AFI technique
- go in each quadrant
- nothing btwn. calibers
- once you start, commit to it
- identify depth anterior to posterior
- do not apply too much pressure & keep transducer straight up
- do NOT tilt
Neurulation
- ectoderm origin
- made up of neural tube, neural groove, vesicles
- closure at 6 weeks
What is the result of neurulation
central nervous system (CNS)
Central Nervous System (CNS)
- brain starts to develop from cranial end of neural tube
- won’t see each individual structure, likely only rhombencephalon
- 3 primary ‘bubbles’ further divide
How does the spine develop?
all 3 pieces of bone surround hypoechoic cord
3 pieces of bone that make up the spine
- anterior vertebral body (red arrows)
- posterior lamina (blue arrows)
- cartilage in between
Purpose of cartilage in the fetal spine
allows for flexibility, rapid growth, & movement through birthing canal
Lower limit of spinal cord in fetus
- conus medularis (lower limit) = S2
- spinal dura mater = S2
Lower limit of spinal cord at birth
- conus medularis = L3
- spinal dura mater = S2
Lower limit of spinal cord in adults
- conus medularis = L1 or L2
- spinal dura mater = S2
- subarachnoid space = S2
How to find the cranium
- identify cranium as oval echogenicity by approx. 12 weeks LMP
- always look for bony calvarium
- intracranial structures (ex. falx line) observed in axial plane
- first identify long axis fetus, scan to cranium, rotate 90 degrees
What positions can the baby be in?
head down, breech, transverse
