First Trimester Sonography Flashcards
What is the potential space between the uterus and rectum where free fluid naturally accumulates?
Posterior cul-de-sac
Where are the ovaries in relation to the uterus?
Lateral
What kind of organ are the ovaries?
Intraperitoneal
What are the normal measurements of the ovaries?
Length = 5cm Width = 3cm Height = 2cm
What connects the ovaries to the uterus?
Ovarian ligaments
What ligament encases the ovarian ligaments and uterine vasculature and provides minimal support for the uterus?
Broad ligament
What do studies say about contraindications for ultrasound scanning?
Benefits outweigh the safety concerns
What is the mechanical index?
Output-display standard used to predict the likelihood of non-thermal ultrasound bioeffects
What are the eight components that the sonographer evaluates and identifies in early OB ultrasound?
Chorionic sac, yolk sac, fetal pole, amniotic sac, fetal heartbeats, gestational age, number of fetuses, and uterus/adnexa
Where does implantation occur in the endometrium?
It occurs on one side, not in the center of the endometrium
What is the first sonographic feature of early pregnancy?
The intradecidual sign surrounding the gestational sac
What characteristics indicate an anembryonic pregnancy?
MSD of 25.0 mm
No fetal pole
No yolk sac
What is the diamond ring sign?
When the fetal pole can be visualized on outside of yolk sac
When does the diamond ring sign appear?
Six weeks GA
How should the sonographer measure fetal heart rate?
Using M-mode
What is the double bleb sign?
Amniotic sac can be seen at the same time as the same time as the yolk sac
Amniotic sac and yolk sac with fetal pole between
What is a subchorionic hematoma?
A blood collection that occurs between chorion and decidua
When do the chorion and amnion fuse?
14 weeks GA
What is the chorionic bump?
An irregular bulge from the chorion decidual surface into gestational sac
How does a chorionic bump present?
A hematoma bulging into gestational sac
What is the level of hCG that you should visualize gestational sac?
1900 mIU/mL
When hCG is below 2000, positive pregnancy test but no gestational sac could mean?
Early intrauterine pregnancy, ectopic pregnancy, recent abortion, possible tumor
When hCG levels over 2000, non-visualization of gestational sac could mean?
Ectopic pregnancy, recent abortion, tumor, or false elevation of tests
Most likely ectopic pregnancy
On normal early pregnancy, at what rate does hCG double?
hCG doubles every 1.2-2.2 days for the first 4-6 weeks
How is hCG affected by embryonic death or abortion?
hCG decreases abruptly
How does ectopic pregnancy or retained POC affect hCG?
hCG levels decrease slowly
When is the gestational sac visualized sonographically?
4.5 weeks GA
What is the rate of growth of the gestational sac?
1.1 mm for the first 8 weeks
What is the normal size of the yolk sac?
<6 mm diameter
Where is the yolk sac located?
Outside the amnion
What is the GA at which the embryonic pole is visualized?
5th menstrual week
When should cardiac activity be seen on ultrasound?
6.3 weeks GA
What does CRL of 5mm with no cardiac activity indicate ?
No viable pregnancy
When are the limb buds seen?
8 weeks GA
When are the mandible/maxilla seen?
10 weeks GA
What is the rhombencephalon?
Hypoechoic structure in posterior fetal head
When does rhombencephalon appear?
8-10 weeks GA
What does rhombencephalon look like on ultrasound?
A cyst or defect within the fetal skull
What is midgut herniation?
Intestines elongate and move outside the gut, herniating into umbilical region
When is midgut germination visible?
9-11 weeks GA
Transabdominally, by what MSD should the yolk sac and fetal pole be visualized?
Yolk sac at MSD over 20 mm
Fetal pole at MSD over 25 mm
Transvaginally, by what MSD should the yolk sac and fetal pole be visible?
Yolk sac 8 mm MSD
Fetal pole 16 mm MSD
What heartbeat is suspicious for abnormality at 5-8 weeks GA?
<85 BPM
What location of the gestational sac is highly suspicious for impending abortion?
The cervix
What is another term for blighted ovum?
Anembryonic pregnancy
What is a blighted ovum?
When gestational development arrested before the embryo formed
What are differential diagnoses for blighted ovum?
Early IUP
Pseudogestational sac of ectopic
What is embryonic death?
Absence of cardiac activity when the embryonic pole can be seen on TAS or with CRL of 5 mm and no cardiac activity
When is follow up ultrasound indicated for embryonic death?
When an embryo with CRL less than 5 mm has no cardiac activity
What are sonographic indications of threatened/spontaneous/missed abortion?
Gestational sac extending into cervix
Deformed sac and embryo
Embryonic without cardiac activity
When subchorionic hemorrhage is present, where is it typically seen?
With the placental edge to one side
What is gestational trophoblastic disease?
When abnormal trophoblast cells grow in the uterus after conception
What is a hydatidiform mole?
When fetal tissue is absent, resulting in degenerating placenta
Cluster of fluid filled sacs in the uterus
How often are hydatidiform moles malignant?
15-25% of the time
What is the sonographic appearance of a hydatidiform mole in the first trimester?
Echogenic or hyperechoic
What is the sonographic appearance of a hydatidiform mole in the second trimester?
Echogenic masses with cystic spaces
What are theca lutein cysts?
Benign neoplasms
Abundance of cysts within the ovaries
How do theca lutein cysts appear sonographically?
Large, multilocular, bilateral cysts
What is an invasive mole?
When molar pregnancy has infiltrated the myometrium and remains within the uterus
What is a mole referred to once it metastasizes?
Choriocarcinoma
What is a partial or incomplete mole?
When a triploid karyotype and three sets of chromosomes are accounted for in the fetus
What are the differential diagnoses considered when gestational trophoblastic disease is suspected?
Complete mole or partial mole
Hydropic regeneration of placenta
Retained POC
Degenerating leiomyoma
What percentage of pregnancies are ectopic?
1.4%
What percent of ectopic pregnancies cause maternal death?
25%
1/4
What percent of ectopic pregnancies are tubal?
95%
Where else can ectopic pregnancies be found?
Abdomen
Ovary
Cervix
What are risk factors for ectopic pregnancies?
Infertility
PID (pelvic inflammatory disease)
Prior ectopic
H/O tubal surgery
Who is more likely to have intrauterine and ectopic pregnancies?
Those undergoing IVF or ovarian ovulation induction treatment
What are ultrasound findings associated with ectopic pregnancy?
Adnexal ring sign and a large amount of fluid accumulated in cul-de-sac
Where else might blood/fluid be found in ectopic pregnancy?
In the adnexa
Does a normal ultrasound 100% rule out ectopic pregnancy?
No
When is a followup ultrasound needed in regards to yolk sac size?
If the yolk sac is greater than 7 mm after 9 weeks
When is the yolk sac no longer visible?
12 weeks
At what rate does the embryo grow?
1 mm per day
What kind of structure is the yolk sac?
Extraaminotic
What is the most accurate biometric measurement in the first trimester?
Crown-rump length
Sonographic detection of what is possible before the patient develops signs/symptoms?
Pregnancy failure
What is a leading cause of pregnancy-related deaths in the first trimester?
Ectopic pregnancy
What percent of pregnancies are ectopic?
1%
When is cornual ectopic present?
Advanced gestation stage
What are indications of cornual ectopic pregnancy?
Severe hemorrhage and maternal shock
When are heterotopic pregnancies more common?
Pregnancies of assisted reproduction
What are the steps for checking for IUP?
- Assess endometrial cavity for a gestational sac
- Use TV to assess anterior and posterior cul-de-sacs for free fluid and abd bleeding
- Assess adnexal regions in trans and sag (ovaries, ectopic GS)
What can happen when the gestational sac embeds within the myometrium and cesarean scar implantation?
Uterine rupture
What is a normal volume for fluid in the posterior cul-de-sac?
5-21 mL volume
What happens in a subchorionic hemorrhage?
The placenta separates from the underlying uterine wall, leaving blood between the amniotic sac and uterine wall
What is true of subchorionic hemorrhage?
They can be seen on ultrasound but are not always associated with poor fetal outcomes
What is a hemorrhagic cyst?
Bleeding inside an ovarian cyst
Looks like marble in appearance on serial US exam
Which type of twin pregnancy can be considered high risk?
Monochorionic because they share vasculature
What is an endometrioma?
Found in the ovary
Causes minimal changes on ultrasound, and has homogenous and ground glass appearance
What should be the clinical application of the first trimester?
Confirming IUP and documenting fetal cardiac activity
What is a pregnancy of uncertain viability?
An intrauterine gestational sac with no embryonic heartbeat and no definitive signs of pregnancy failure
Where are the majority of ectopic pregnancies located?
Ampulla and isthmus of fallopian tube
What pregnancies are associated with the lambda sign?
Dichorionic
What should not be used as part of an early pregnancy ultrasound scan?
Pulsed wave doppler
What are definitive signs of failed pregnancy?
A CRL > or = 7 mm w no cardiac activity
A MSD > or = 25 mm w no embryo
Where is the uterus in relation to the bladder?
Posterior
What kind of structure is the bladder?
Extraperitoneal
An ovarian mass seen in transverse can be a what?
Dermoid cyst
Where can free fluid be found?
Anterior and posterior cul-de-sacs
How should the bladder be filled for TV and TA ultrasound?
Empty for TV
Full for TA
What is synonymous with gestational age?
Menstrual age
What age differs from menstrual age?
Conceptional age
What can occur in a suspected ectopic pregnancy?
Pseudosac can be misidentified as gestational sacs
What does a hemorrhagic cyst show on color doppler?
No blood flow
What does a simple ovarian cyst appear like on ultrasound?
Has thin, well-rounded wall with excellent sound transmission and no internal irregularities
How does a malignant adnexal mass appear on ultrasound?
Has solid papillary projections and presence of vascular flow on color and pulsed wave doppler
When is US evaluation of fetal cardiac activity typically seen?
When the embryo is 7 mm in length
What does a pseudo sac share sonographic characteristics with?
Gestational sac
How do corpus luteum cyst and ectopic pregnancy differ?
Corpus moves with the ovary and is surrounded by regular tissue
Ectopic moves separately and has echogenic ring
What are normal hCG levels at 3 weeks GA?
5-50 mIU/mL
What are normal hCG levels at 4 weeks GA?
5-426 mIU/mL
What are normal hCG levels at 5 weeks GA?
18-7340 mIU/mL
What are normal hCG leves at 6 weeks GA?
1080-56500 mIU/mL
What are normal hCG levels at 7-8 weeks GA?
7650-229,000 mIU/mL
What are normal hCG levels at 9-12 weeks GA?
25,700-288,000 mIU/mL
What is the hCG level considered the threshold for a negative pregnancy test?
Less than 5 mIU/mL
What is the hCG level considered the threshold for a positive pregnancy test?
Above 25 mIU/mL
Why should hCG levels not be used to date a pregnancy?
The numbers vary so widely
What is a qualitative hCG test?
Determines if there is hCG in the blood
What is a quantitative hCG test?
Determines how much hCG is in the blood
What is indicated when hCG levels are lower than expected?
Pregnancy dating miscalculation
Miscarriage
Blighted ovum
Ectopic pregnancy
What is indicated when hCG levels are higher than expected?
Pregnancy dating miscalculation
Molar pregnancy
Multiple pregnancies
When do hCG levels return to normal after pregnancy loss?
After 4-6 weeks
What are indications for a first trimester OB ultrasound?
Vaginal bleeding Abdominal pain Positive pregnancy test Hypotension Hyperemesis gravidum (vomiting)
What are contraindications for first trimester OB ultrasound?
None for TA
TV contraindication for hypotenstion
Avoid color and spectral doppler imaging
What do you ask a patient who comes in with abd pain and a positive pregnancy test?
LMP Vaginal bleeding Pregnancy history Ectopic risk factors - previous EP, PID, pelvic surgery, IUD, ovulation induction Describe/ point to pain
What would you do before giving the patient a TV ultrasound?
Document statement
Get abdominal imaging to rule out cysts or abd bleeding
Proceed w TV
What are differential diagnoses for bleeding patient?
Very early IUP w/ corpus luteum cyst
Ectopic pregnancy but early - order hCG
White blood cell count to rule out appendicitis
Molar pregnancy, miscarriage, blighted ovum
How does the sonographer determine chorionicity and amniocity before 10 weeks?
Identify number of GS, number of amniotic sacs, , number of yolk sacs
How does the sonographer determine chorionicity and amnionicity after 10 weeks?
Identify sex discordance, number of distinct placentas, characteristics of intertwin membrane, and lambda sign
How do we know we are looking at monozygotic pregnancy?
Fetuses are the same sex and share placental site
No membrane between cord insertion sites
How do we know we are looking at dizygotic pregnancy?
One fetus is male and the other is female
Separate amniotic sac and placental site with thick membrane between
When are we unsure whether the pregnancy is mono or dizygotic?
If the only information we have is that they are the same gender
What is the frequency of US exams for dichorionic pregnancies?
3-4 weeks
What is the frequency of US exams for monochorionic pregnancies?
2-3 weeks
