Sono Science
Do high or low frequency yield better image resolution
What is suboptimal dating?
Confirming US >22w0d
When should anatomy scans be performed?
18-22 weeks
What is a normal AFI?
5-25cm
Define placenta previa
Placental edge within 2cm of internal os
What is gain?
Gain refers to amplitude of returning sound waves, controlling brightness vs. darkness of screen
What is the discrepancy of LMP to US to redate gestational age at <9 weeks?
>5 days
Name 5 indications for a fetal echo
Suspected fetal cardiac structural or functional abnormality, heart rate abnormality or arrhythmia, extracardiac anomaly or hydrops, chromosomal abnormality, NT >3.5mm, IVF, monochorionic twin gestation, 1st degree relative to fetus with cardiac defect, 1st or 2nd degree relative to fetus with mendelian syndrome and childhood cardiac manifestation, prior fetus with heart block in setting of anti-Ro or anti-La antibodies, retinoid exposure, pregestational diabetes, or phenylketonuria
What is severe polyhydramnios?
>35cm
What artery is measured to assess for fetal anemia?
Middle Cerebral Artery
What frequency do ultrasound waves travel at?
Above 20,000 Hz
When should nuchal translucency be measured?
11 to 14 weeks
Define velamentous cord and what can be associated with velamentous cord insertion
When the umbilical cord inserts into the membranes, not the placenta itself. The umbilical vessels travel unprotected by Wharton jelly and can be a risk factor for vasa previa
Top 3 etiologies for polyhydramnios
Idiopathic, Fetal anomalies, Diabetes
What measurement reliably identifies fetuses with moderate to severe anemia?
What two indices are all ultrasound devices required to display for safety?
Mechanical and thermal
1) CRL >7mm no heartbeat
2) Mean sac diameter 25mm or greater with no heartbeat
3) Gestational sac w/ no yolk sac and no heartbeat 14 days later
4) Gestational sac w/ yolk sac and no heartbeat 11 days later
Risk of PAS w/ 3 prior CS and placenta previa?
61%
IOL timing for oligohydramnios
36w0d to 37w6d
What percent of major fetal anomalies can be identified on standard US?
Approx 60%
Ultrasound transducers contain what type of crystals that convert electrical energy into sound waves?
Piezoelectric crystals
What NT measurement is associated with increased risk for fetal structural or genetic abnormalities?
>3mm
Name 3 of 5 US criteria for Placenta Accreta Spectrum
1) Placenta Lacunae
2) Attenuation or thinning of the retroplacental myometrium
3) Disruption of bladder-uterine serosal interface
4) Bridging vessels from bladder - serosal interface
5) A placental "bulge" that pushes outward and distorts contour of uterus
Fetal urination per day in late pregnancy
1L/day
Why measure Umbilical Artery for S/D ratio? And what is an abnormal measurement?
Differs from other vessels that it normally has forward flow throughout the entire cardiac cycle. Abnormal >95% for gestational age.