Carney - Limited OB Ultrasound USAFP-1

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OB Ultrasound for the Family Physician:

OB Ultrasound for the Family Physician Leo A. Carney, III DO LCDR, MC, USN Assistant Program Director Family Medicine Residency Naval Hospital Pensacola


Objectives Review the indications for first trimester ultrasound Discuss utilization of ultrasound Review measurements and how they apply to dating criteria Discuss how to document an ultrasound in the medical record

Indications (1st Trimester):

Indications (1 st Trimester) Dating of pregnancy Size vs dates discrepancy; multiple gestation determination * (1 st Trimester)* Vaginal bleeding Abdominal or pelvic pain: rule out ectopic pregnancy/ torsion/ heterotopic pregnancy/ ovarian cyst ***Not credentialed to do*** To confirm viability

Pregnancy Dating with 1st trimester ultrasound:

Pregnancy Dating with 1 st trimester ultrasound The only utility for “routine” ultrasound as determined by the RADIUS study Early dating is the most accurate (+/- 5-7d or 8%) Better defines timing for later testing and interventions Triple/Quad test Tocolysis/Steroids Reduces the incidence of induction for postdates


Measurements Mean Sac Diameter Should be measured in 3 dimensions May be all that is visible at the discriminatory zone; IUP best confirmed with some fetal element, such as a yolk sac

The Early Gestational Sac:

The Early Gestational Sac


Measurements Embryonic Crown-Rump Length (CRL) Measurement of a CRL with fetal cardiac activity is the best measurement for dating purposes Accurate through the 12 th week of gestation

Early Embryo:

Early Embryo

The Crown-Rump Length:

The Crown-Rump Length

Late 1st Trimester—10 week:

Late 1 st Trimester—10 week

Typical Measurements:

Typical Measurements There are tables for determining gestational age based on: Gestational Sac Measurement Crown-Rump Length All of the U/S machines at NHP contain software which perform these calculations. The measurements will trigger the gestational age determination.

Determination of Gestational Age:

12 Determination of Gestational Age Gestational Age (weeks) Sac Size (mm) CRL (mm) 4 3 5 6 6 14 7 27 8 8 29 15 9 33 21 10 31 11 41 12 51 13 71

Order of Fetal Structures :

13 Order of Fetal Structures Gestational sac – 4 to 5 weeks Yolk sac – 5 to 6 weeks Fetal pole - 6 to 7 weeks Cardiac Activity - 6 to 7 weeks.

Early Pregnancy Failure:

Early Pregnancy Failure Failure of appropriate interval growth by US of embryo Fetal pole/yolk sac should be seen by the time the MSD is 20 mm (not as accurate as FCA though) Fetal Cardiac Activity should be seen by the time the CRL is 4mm (5mm per AIUM) If not, may repeat the u/s in one week

Rule out ectopic:

Rule out ectopic Classic triad—amenorrhea, vaginal bleeding, pain Must have a high index of suspicion Even more so in the face of risk factors Three primary tools for evaluation Physical exam Quantitative β HCG Ultrasound

Lab and Ultrasound:

Lab and Ultrasound Discriminatory Zone—the quant β -hCG level at which one would expect to be able to identify an intrauterine pregnancy For vaginal sonography—1200-1500 (1000-2000 per ACOG) For abdominal sonography—3000-4000 If the quant β -hCG is at or above the discriminatory zone, AND no IUP can be identified, the pregnancy may be ectopic

Multifetal Gestation:

Multifetal Gestation

Fetal Number:

Fetal Number

Other applications:

Other applications ***Not credentialed to do*** Evaluation of gynecologic structures Uterus—position, fibroids Adnexae—masses, corpus luteum Early screen for chromosomal anomalies Nuchal translucency measurements


Documentation Whether obtained abdominally or vaginally, the following information should be obtained and documented: Presence or absence of IU gestational sac and identification of an embryo if possible Fetal number Presence or absence of fetal cardiac activity Crown-rump length Evaluation of uterus and adnexal structures and presence of free fluid (per AIUM) ***Not credentialed to do***

What Measurement is the most accurate for ultrasound dating? :

22 What Measurement is the most accurate for ultrasound dating? Crown Rump Length – Up to the 12 th week of life.

Second and Third Trimester OB Ultrasound:

Second and Third Trimester OB Ultrasound

Types of 2nd/3rd Trimester Ultrasound:

Types of 2 nd /3 rd Trimester Ultrasound Standard – Anatomic Survey Limited – Targeted to answer a question Specialized – Targeted anatomic 24


Application Fetal Cardiac Activity Fetal Lie Fetal Number Placental Location AFI BPP/Modified BPP

Fetal Life:

Fetal Life Positive cardiac activity Fetal death Absence of cardiac activity for at least 2-3 minutes Ideally confirmed by two or more examiners

Fetal Presentation:

Fetal Presentation Lie - relationship of long axis of fetus to the long axis of the mother Longitudinal Transverse Oblique Presentation – part of the fetus closest to maternal pelvic inlet or cervix Cephalic (vertex, sinciput, brow, face) Breech Shoulder Compound



Fetal Spine:

Fetal Spine

Longitudinal Cephalic:

Longitudinal Cephalic

PowerPoint Presentation:

Abdomen Diaphragm Placenta Lung Cord Insertion Bowel Longitudinal View

Fetal Number:

Fetal Number “Surprise Twin” should be a rare event Underestimation errors Not evaluating fundal region Not making sure fetal head and body are connected

Fetal Number:

Fetal Number

Fetal Number:

Fetal Number

Placental Location:

Placental Location Anterior/Posterior/Lateral/Fundal Placenta Previa Marginal Partial Complete Low-Lying

Placental Location:

Placental Location

Placental Location:

Placental Location Placenta Previa 0.5-1% of pregnancies Difficult to diagnose before 3 rd trimester potential for change with lengthening of lower uterine segment Over distended bladder can give erroneous impression of previa



Placenta Previa:

Placenta Previa A- fetal head B- ant uterine wall C- full bladder D- placenta E- placental lakes F- cervical canal

Amniotic Fluid Volume:

Amniotic Fluid Volume “The importance of amniotic fluid to fetal well-being cannot be overstated” Peter W Callen Ultrasonography in Obstetrics and Gynecology

Amniotic Fluid Volume:

Amniotic Fluid Volume Not a stagnant pool Complete turnover of total volume occurs in about one day Generation primarily by fetal kidneys/bladder Removal primarily by fetal swallowing

Amniotic Fluid Production:

Amniotic Fluid Production

Amniotic Fluid Index (AFI):

Amniotic Fluid Index (AFI) Subjective Assessment Fluid volumes classified as normal, high, or low for gestational age Single duplex pocket measurement 1-2 cm pocket represents oligo, > 8 cm represents Polyhydramnios 4 Quadrant Most reproducible/accurate

4 Quadrant (AFI):

4 Quadrant (AFI) Landmarks Umbilicus Linea nigra Linear transducer head placed along mother’s longitudinal axis and held perpendicular to the floor in the sagittal plane

4 Quadrant (AFI):

4 Quadrant (AFI) Maximum vertical measurement of the largest fluid pocket in each quadrant is measured Cord or extremities may traverse the pocket, but may not be measured as part of the vertical depth Measurements from each pocket are summed to give the total volume



Amniotic Fluid Index:

Amniotic Fluid Index Normal term AFI = 5 – 20 cm Mean AFI 36-42 weeks = 12.9 +/- 4.6cm (Phelan) Oligohydramnios < 5 cm Polyhydramnios > 20 cm or > 8cm pocket

Amniotic Fluid Index (AFI):

Amniotic Fluid Index (AFI)

AFI Pitfalls:

AFI Pitfalls Excessive transducer pressure Cord-filled pockets should not be used Obese patients may introduce scatter that creates artifact echoes May overcome with lower frequency transducer Not measuring low in the uterine cavity

Biophysical Profile (BPP):

Biophysical Profile (BPP) Combination of NST with 4 real-time ultrasound observations 2 points given to each observation that is normal or present Maximum 30 minute time frame

PowerPoint Presentation:

Components of the 30 minute Biophysical Profile Score Component Definition Fetal movements > 3 body or limb movements Fetal tone One episode of active extension and flexion of the limbs; opening and closing of hand Fetal breathing movements > 1 episode of > 30 seconds in 30 minutes - Hiccups are considered breathing activity. Amniotic fluid volume A single 2 cm x 2 cm pocket is considered adequate. Non-stress test 2 accelerations > 15 beats per minute of at least 15 seconds duration .

PowerPoint Presentation:

Perinatal Mortality and the Biophysical Profile Score Score Perinatal Mortality/1000 8 - 10 1.86* NORMAL 6 9.76 EQUIVOCAL 4 26.3 2 94.0 0 285.7 *0.8/1000 for structurally normal fetuses with a normal test within 7 days Derived from:Manning FA et al. Am J Obstet Gynecol 1990;162:703.;Manning FA et al. Am J Obstet Gynecol 1985;151:343. ;Manning FA ( ed ): Fetal Assessment: Principles and Practices. Norwalk CT, Appleton and Lange 1995, p 221.


BPP Each of the 5 components of the biophysical profile score do not have equal significance. Fetal breathing movements, amniotic fluid volume , and the non-stress test are the most powerful variables.

Modified BPP:

Modified BPP Combines NST (short-term indicator of acid/base status) AFI Considered normal if NST is reactive and AFI is >5 cm Greater than 99.9% NPV (negative test and no disease) for stillbirth within 7 days

Documentation of Limited US:

Documentation of Limited US Fetal Number Presence of Cardiac Activity Fetal Lie/Presentation Placental Location Fluid Status Ex: Singleton, +CA, Vertex, Ant. Plac., Nml Fluid

3D/4D Ultrasounds:

3D/4D Ultrasounds No medical indication Technology has been around for about 20 years Utilized for last 5-10 years 56

3D/4D Ultrasound (cont.):

3D/4D Ultrasound (cont.) 57



Primary Resources:

Primary Resources Lyndon M. Hill, MD ; Institute for Advanced Medical Education; Joseph Woo's Obstetric Ultrasound International Society for Ultrasound in Obstetrics and Gynecology ACOG Practice Patterns and Practice Bulletins Phelan, et al. Amniotic Fluid Volume Assessment with the 4 Quadrant Technique, Journal of Reproductive Medicine, vol7, July, 1987. Peter W Callen Ultrasonography ini Obstetrics and Gynecology 4 th ed , WB Saunders, 2000

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