Lecture 1B - OB US Exams Flashcards
First trimester
1-13 weeks
Second trimester
14-26 weeks
Third trimester
27 weeks until ‘term’ (around 40 weeks)
How is pregnancy confirmed
presence of gestational sac. Want it to be intrauterine pregnancy
What are we looking for in a gestational sac
Embryo + cardiac activity
Yolk sac
What mode is used to confirm fetal HR
M-mode
Purpose of first trimester assessment of fetus. Give example
Assess for abnormalities
Increased nuchal translucency measurement (fluid under neck) - chromosomal abnormalities
Non-viable pregnancies
Ectopic
Hydatidiform moles
Purpose of second trimester assessment (4)
Assessment of viability (cardiac activity) Fetal number/growth (biometry) Fetal environment (amniotic fluid, placenta) Maternal structures (uterus, cervix)
Different names for second trimester assessment
Routine Basic Level 1 Morphology Anatomy Complete 20 week
Specialized examination (2)
Level 2
Targeted
Indications for level 2 (specialized) examination
Anomaly suspected on level 1
Family Hx
Abnormal blood tst
Third trimester assessment
Limited assessment and less common
Indications for third trimester assessment (8)
- Gestational diabetes
- Maternal measurements inappropriate for gestational age
- Cannot feel the baby
- Position check before birth
- Placental location
- Incompetent cervix
- Pathology
Transabdo probe
3-5 MHz
Transvag probe MHz
5-10 MHz
2 non-invasive probes used in later pregnancies
transperineal and translabial (3-5 MHz)
ALARA
as low as reasonably achievable
Minimizing output intensity (2)
Reducing power settings on machine
Using doppler only as necessary
Teratogen
malformaiton of embroy (sound absorbed by heat is a potential)
Thermal intex
Measurement of US conditions that can change temp of tissue
Thermal index (TI) of 1 means
The tissue may increase in temp 1 degree
What is the threshold for potentially hazardous conditions
1.5-2 degrees
TI s (soft tissue)
less than 8 weeks
TI b (bone)
more than 8 weeks
How much can doppler US cause an increase
> 1 degree if held in same spot over 30 sec
Mechanical index should be less than
1.9
cavitation
Non-thermal bioeffect - creation, oscillation, collapse of bubbles. higher potential in gas-containing structures
T/F there are no confirmed bioeffects
true
T/F With respect to bioeffects, most human studies have been inconclusive
true
