Obestetric ultrasound

Ultrasound Basics in Obstetrics

Obstetric transvaginal and transabdominal US plays apivotal role in obstetric care, many women nundergoUS examination without no adverse effect on the fetus.

Female Anatomy Review:

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, and before empting the bladder.

Fundus of uterus

cervix


It’s used in early pregnancy before 16 weeks because of close proximity of the intravaginal probe allowing better resolution of the pelvic organ ,uterus and pregnancy

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

Now to ultrasound with a fetus inside!

Try to have a system when scanning transabdominally:Start at suprapubic area with indicator pointing to patient’s 9 o’clockprovides a conventional coronal image with left side of monitor screen as patient’s positional rightMove transducer cranially this will allow you to see coronal sections of entire uterus & fetusNow change indicator to point at 12 o’clock  provides conventional sagittal image with left side of screen as patient’s cranial endThis will allow you to see sagittal sections of fetus coronal view sagittal view indicator
indicator

The Report and Criteria for Assessment 1. Record if transabdominal and/or transvaginal scan performed. 2. Clinical history and indication for examination. LMP or EDD by dates. 3. Dating: If a fetal pole is present, the CRL used for gestational age calculation is recorded. If no fetal pole is present, the mean gestational sac diameter is used to assess gestational age. Presence or absence of a yolk sac should be noted when a fetus is not seen. Calculate EDD by Ultrasound if more than 4 days different from EDD by dates , ultrasound in 7 days may be recommended .


4. Fetal Viability: Transvaginal Scanning is recommended in all pregnancies of <8 weeks gestation if no fetal heart motion can be recorded transabdominally: If the above criteria are not present, i.e. pregnancy is < 6 weeks gestation, a repeat ultrasound in 7 days may be recommended in the report. If fetal viability is confirmed but PV bleeding persists or worsens, reassessment may be indicated.

5. Ectopic Pregnancy: Uterine cavity appearance, ovarian appearance and site of corpus luteum, presence, size and site of the suspected ectopic, presence of peritoneal fluid including under the diaphragm. Correlation with quantitative b HCG recommended. 6. Multiple Pregnancies: Chorionicity should be reported and is most accurately assessed during the 1st trimester. Two completely separate gestational sacs confirm a dichorionic twin pregnancy. The CRL and FHR of each twin should be stated.

If there is only one gestational sac, the pregnancy is monochorionic and in these cases, the yolk sac and amnion should be clearly assessed. If there are two separate yolk sacs and a separating amnionic membrane, the pregnancy is mono-chorionic/diamniotic. If there is only one gestational sac with only one yolk sac, and a single amniotic cavity,the pregnancy is monochorionic/monoamniotic.


7. Gestational Trophoblastic Disease: A molar pregnancy is suspected in the presence of cystic hydropic change to placental tissue.8. Uterine and adnexal Masses – Describe the dimension, nature and location of the mass. Presence of free fluid.

First Trimester

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

First trimester

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

First Trimester

Measuring Gestational Age:crown rump length (CRL)Approximately estimates GA from 7-12wks gestation Measure longest length of embryo excluding limbs or yolk sacA Rule of thumb of estimating GA: 6wks + CRL(mm) = 6wks+daysEstimating due date: For 1st trimester if GA measures within 7days of EDD by LMP then do not change EDDFor 2nd trimester if GA measures within 10days of EDD by LMP  then do not change EDDIf ultrasound provides EDD more/less than the 7 or 10 days, then EDD is changed to ultrasound EDD Once GA confirmed with first trimester CRL, EDD should NOT be changed in further CRL measurements Measured CRL
Measured CRL


Other measurement parameters used to estimate gestational age Biparietal diameter Femur length Abdominal circumference The various parameters can be used in a specific equation providing estimated fetal weight (EFW)


First Trimester:
Thickened Nuchal Tanslucency (NT):One of the parameters used in sequential screening (SS) for Down’s syndrome in first trimesterSS: Pregnancy associated plasma protein levels, hCG levels, NT thickness Measured during 11-14 wks gestational ageSeen on sagittal image as increased subcutaneous non-septated fluid in posterior fetal neckMeasurement >3mm usually considered abnormal, however exact cut off measurements are dependent on maternal age/gestational ageDetection rate of screening for Down’s Syndrome in first trimester:-sequential screening with NT: 82-87%

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?

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 -So what explains the difference between the GA from 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.

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?

Case 2

Question: Is this a normal ultrasound finding?  NO!!! This case is suggestive of a Missed Spontaneous Abortion with a non-viable gestational sacAt 9wks GA expected ultrasound findings include: yolk sac, embryo, fetal heart beatCRL of embryo measuring close to 8wks GA

Approximately 50% of early 1st trimester spontaneous abortions are attributed to chromosomal abnormalities. Most common is a non-viable trisomy. In comparison, 2nd trimester abortions are less likely due to chromosomal abnormalities.

Case 3

A 24 y/o female G0P0 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 chlamydia/gonorrhea 2 years ago that was appropriately treated with antibiotics. Physical Exam: She is afebrile, tender to palpation to RLQ with palpable right adnexal mass. What initial test should be done in the ED? Pelvic ultrasound imaging Urine hCG levels


Case 3
RESULTS: - Elevated urine hCG levels suggestive of pregnancy. 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 urterine cavity

Question: Is this most likely just a regular intrauterine pregnancy?

Case 3
This case is most likely a Tubal Ectopic Pregnancy! 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 Does this patient have any risk factors for an ectopic pregnancy?

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:chlamydia/gonorrhea pelvic inflammatory disease of tubal ligation

Placenta Attachment

Ultrasound can be used to determine position of placenta attachment in the uterine cavity. This information may help in management of delivery during labor. Placenta can be seen attached to any segment of uterine cavity. Placenta is seen as hyperechoic thickening of uterine cavity. Some examples:
Anterior placenta
Posterior placenta

Case 4

32 y old G1P0 at 32 wks GA comes in to the Emergency Department with complaints of 2 hrs of bright vaginal red bleeding , She denies pain, uterine contraction, leakage of fluid or trauma. On exam, abdomen is soft and fetal heart tones are normal. She is visiting from out of town and does not have any of the prenatal records available. transabdominal ultrasound and you see the following:
placenta
cervix

Case 4

PLACENTA PREVIA : placenta attachment completely covering the internal os of the uterine cervix Normally lower placental edge should be at least 2 cm from the margin of the internal cervical os. When seen in early pregnancy, it is expected to resolve as placenta often transmigrates away from internal os as uterine expands through out pregnancy Often presents as painless bleeding in 2nd or 3rd trimester for <2hrs duration Medical management: Can often be observed after first episode bleeding, multiple episodes may necessitate delivery Unresolved placenta previa will deliver by c-section There is grades of placenta previa:

placenta

cervix


PLACENTA ABRUPTION: premature separation of placenta from endometrium. Commonly presents as painful vaginal bleeding with irregular contractions Bleeding is continuous once starts and is most common cause of coagulopathy in pregnancy Ultrasound findings:

myometrium

Hemorrhage from separation of placenta from endometrium
placenta
fetus

Case 5

25 y/o G1P0 at 14wks GA dated by LMP comes in for her first prenatal care, Pregnancy was confirmed by multiple urine pregnancy test 7 wks ago. Pregnancy has been complicated with recent vaginal bleeding with out pain. Uterus larger than expeceted for a 14wk pregnancy. QUESTION: How would you describe this finding with in the uterine cavity?

Case 5

The ultrasound is a classic example of a SNOW STORM appearance with in the uterine cavity


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Case 5

this picture is diagnostic for complete molar pregnancy2 types: complete mole (no fetal parts) vs incomplete mole (partial fetal parts)Common presentation of Complete Molar Pregnancy:Ultrasound findings with in uterine cavity:Complete mole: pathognamonic “snow storm” appearance with absence of fetal heart beat or fetal partsIncomplete mole: presence of abnormal incomplete fetal parts with absence of fetal heart beat

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