5. Transabdominal Ultrasound
• Transabdominal approach :
– Lower frequency, lower resolution image
– Curved linear transducer
– Better visualized with full bladder
• Can see coronal and sagittal views of
organs and fetus
Indicator on side
of transducer
bladder
uterus
vagina
cervix
bladder
6. Transvaginal Ultrasound
• Transvaginal approach:
– Higher frequency, higher resolution image
– Endocavitory probe
– Better visualized with empty bladder
– Can see sagittal or coronal view of uterus
– RULE OF THUMB: if possible attempt transabdominal before considering transvaginal to avoid more
invasive procedure.
Fundus of
uterus
cervix
7. How to ultrasound with a fetus inside!
• Start at suprapubic area with indicator pointing to patient’s 9 o’clockprovides a
conventional coronal image with left side of monitor screen as patient’s positional
right
- Move transducer cranially this will allow you to see coronal sections of entire uterus &
fetus
• Now change indicator to point at 12 o’clock provides conventional sagittal
image with left side of screen as patient’s cranial end
- This will allow you to see sagittal sections of fetus
corornal view
sagittal view
indicator indicator
9. First Trimester
1. Confirm viable pregnancy:
• Gestational Sac (GS):
– Visible at 4-5wks GA with transvaginal US
– Visible at 6 wks GA with transabdominal US
– echogenic ring with anechoic center within uterine cavity
– Measure by Mean Sac Diameter: average dimensions of width/length/height of sac
– GS size increases by about 1mm/day in early pregnancy
– Discriminatory zone: serum hCG level in which gestational sac is expected to be visible by US :
hCG >2000 mIU/ml
Gestational sac
Endometrial decidua
10. First trimester
1. Confirm viable pregnancy:
Yolk Sac: bright ring with anechoic center located inside GS seen at 5wk GA.
Fetal Pole: represents fetal development at somite stage. Can be seen by transvaginal US as
thickening of yolk at 6wks GA.
Fetal heart beat : usually seen around the time fetal pole is present, further confirming viability
Yolk sac
Fetal pole
11. First Trimester
2. Measuring Gestational Age:
• crown rump length (CRL)
– Approximately estimates GA from 7-12wks gestation
– Measure longest length of embryo excluding limbs or yolk sac
– A Rule of thumb of estimating GA: 6wks + CRL(mm) = 6wks+days
Estimating due date:
– For 1st trimester if GA measures within 7days of EDD by LMP then do not change EDD
– For 2nd trimester if GA measures within 14days of EDD by LMP then do not change EDD
– If ultrasound provides EDD more/less than the 7 or 14 days, then EDD is changed to ultrasound EDD
– Once GA confirmed with first trimester CRL, EDD should NOT be changed in further CRL
measurements
• 5 – 9 weeks : use of mean GS diameter
• 6 – 12 weeks : use of CRL (most accurate dating of early pregnancy)
• After 12 weeks : use of BPD
Measured
CRL
Measured
CRL
12. First Trimester
3. Multiple pregnancy:
• Chorionicity
– Type of placentation
– Prenatally by USG
– Postnatally by examining membranes
• Usg determination for chorionicity
– Numbers of sacs
– Placenta
– Sex
– Intertwin membrane
– Lambda & T sign
Ideal time to assessing chorionicity is before 14 weeks
13.
14. First Trimester:
4. Thickened Nuchal Tanslucency (NT):
• One of the parameters used in sequential screening (SS) for Down’s syndrome in first
trimester
– SS: Pregnancy associated plasma protein levels, hCG levels, NT thickness
• Measured during 11-14 wks gestational age
• Seen on sagittal image as increased subcutaneous non-septated fluid in posterior fetal neck
• Measurement >3mm usually considered abnormal, however exact cut off measurements are
dependent on maternal age/gestational age
• Detection rate of screening for Down’s Syndrome in first trimester:
– sequential screening with NT: 82-87%
– NT alone: 64-70%
15. First Trimester:
4. Procedure under USG guided:
• Chorionic villi sampling/ Amniocentesis
• S&C
• Feticide/ Fetal reduction–potassium chloride
20. US poor prognostic indicators of
pregnancy include:
• No yolk sac, where:
– MSD > 8 mm
– embryo seen
• Irregular gestational sac
• Low position of the gestational sac
21. Pregnancy of unknown location
• PUL = +ve pregnancy test + no IU or Ext.U
pregnancy in US scan
• Differential diagnosis is:
– very early pregnancy, not detected with
ultrasound
– complete miscarriage
– unidentified ectopic pregnancy
24. Ectopic pregnancy
A 24 y/o female comes in to the ED with acute onset of right lower quadrant
abdominal pain that started late last night. She is sexually active and unclear of
LMP . She reports that she had vaginal spotting this week which is unusual
because she usually does not spot between periods. Sexual history is significant for
h/o chlamydia/gonorrhea 2 years ago that was appropriately treated with
antibiotics.
Physical Exam: She is afebrile, tender to palpation to RLQ with cervical excitation
What investigation should be done in the ED?
- UPT
- Pelvic ultrasound imaging
25. RESULTS:
- UPT positive
- Transabdominal ultrasound of right adnexa
- Transvaginal ultrasound of uterus
US Findings:
- Trans abdominal US shows echogenic gestational sac with presumable yolk sac
- Gestational sac NOT surrounded by uterine tissue
- Transvaginal US shows empty uterine cavity
Question: Is this most likely just a regular intrauterine pregnancy?
26. Question: Is this most likely a regular intrauterine pregnancy?
NO! This case is most likely a Tubal Ectopic Pregnancy!
Common presentation of tubal ectopic pregnancy:
- Women of child bearing age
- Amenorrhea
- Vaginal bleeding
- Acute lower quadrant pain
Further workup:
- In normal intrauterine pregnancy, serum hCG levels should increase about 60% in 48hrs
- Doing a 48hr serum hCG test that shows <60% increase may further suggest abnormal
pregnancy
BONUS Question: Does this patient have any risk factors for an ectopic pregnancy?
27. • Patient’s h/o of chlamydia/gonorrhea puts her at increase risk of developing tubal
ectopic pregnancy. This is found to be especially true if past infection was an
ascending infection that caused inflammation of fallopian tubes that resolved with
scarring of fallopian tube. This may increase risk of fertilized egg getting stuck in
tube.
• Common risk factors for tubal ectopic pregnancy includes:
– h/o chlamydia/gonorrhea
– h/o of pelvic inflammatory disease
– h/o of tubal ligation
33. Molar pregnancy
• The ultrasound is a classic example of a SNOW STORM appearance with in the
uterine cavity
=
34. MOLAR PREGNANCY:
• A type of benign gestational trophoblastic pregnancy often called “hydatidiform mole”
• 2 types: complete mole (no fetal parts) vs partial mole (partial fetal parts)
• Common presentation of Complete Molar Pregnancy:
– Often have excessively higher than expected hCG levels for gestational age
– abnormal painless vaginal bleeding
– Uterine size larger than expected for gestational age
• Ultrasound findings with in uterine cavity:
– Complete mole: pathognamonic “snow storm” appearance with absence of fetal heart beat or fetal
parts
– Partial mole: presence of abnormal incomplete fetal parts with absence of fetal heart beat
37. Case 1
A 23 year old G1P0 comes in to the clinic to confirm her pregnancy status. Based on
her last menstrual period (LMP) she is 8 wks 2days pregnant. She took a home
pregnancy test yesterday which was positive. To confirm her pregnancy you do the
following:
• Repeat urine hCG test: Positive
• Transvaginal ultrasound:
US findings: Gestational sac and CRL measuring at
7wks gestational age
- There was a detectable heartbeat
Question: Is this a normal pregnancy?
38. Case 1
Question: Is this a normal pregnancy? YES!
Confirmed viability by ultrasound:
- Presence of gestational sac
- Presence of fetal pole with CRL 7wks
- Presence of fetal heart beat
Bonus Questions:
-So what explains the difference between the GA from estimated LMP and the
estimated GA with ultrasound?
- Which EDD should be used as the more accurate due date?
39. Answer to bonus questions
So what explains the difference between the estimated LMP and the estimated GA
with ultrasound?
– Many patients may not remember accurate date of LMP. Most likely discrepancy is due
to miscalculation of original EDD based on last menstrual period.
Which EDD should be used as the more accurate due date?
– Estimated EDD by LMP was 8wks 2days while ultrasound estimates 7 wks.
– Discrepancy in dating is in the first trimester that is more than 7 days apart
– Thus gestational age via ultrasound of 7wks should be used with corresponding EDD
40. Case 2
A 28 y/o G1P0 comes in for her first prenatal visit. Patient has been reliably tacking her menstrual cycle for the
past year. Based on her LMP, her estimated EDD suggests she is 9 wks pregnant. She reports pregnancy
has been uncomplicated. Upon ultrasound you see:
Findings:
- Echogenic getational sac with in uterine cavity, GS measuring 5wks
Question: Is this a normal ultrasound finding?
41. Case 2
Question: Is this a normal ultrasound finding? NO!!!
- This case is suggestive of a Missed Spontaneous Abortion with a non-viable gestational sac
- At 9wks GA expected ultrasound findings include:
- yolk sac, embryo, fetal heart beat
- CRL of embryo measuring close to 8wks GA
Spontaneous abortions:
- Should be evaluated by transvaginal ultrasound
- diagnosed by ultrasound within 20wks of pregnancy
- often not associated with any specific symptoms besides possible first trimester vaginal
bleeding
- Occur in 15-20% of first trimester pregnancies, 80% of which are during first 12wks
pregnancy
