OB imaging Flashcards
What is the difference between transabdominal & transvaginal ultrasounds?
Transvaginal
- more sensitive
- empty bladder
- used only before 12 weeks
Transabdominal
- full bladder
- affected by maternal BMI
- used in all trimesters
What are the indications for ultrasound in the first trimester?
1- diagnosis of pregnancy, location, viability, # of fetuses
2- dating scan: crown rump length 45-84mm
3- nuchal translucency
4- vaginal bleeding or acute abdominal pain
What are the indications for ultrasound in the second trimester?
1- anomaly scan
2- growth scan
3- measurement of cervical length
What are the indications for ultrasound in the third trimester?
1- growth
2- fetal wellbeing assessment: amniotic fluid volume & doppler ultrasound
3- placental localization (esp cases of antepartum hemorrhage)
4- presentation of delivery
When should gestational age be determined?
MAXIMUM by 20 weeks
from 14 weeks & more use HC, BPD, & FL for dating
What is the best time for detection of anomalies?
18-21+6 days
detection rate 40-90% at 20 weeks
- depends on type of anomaly, position of fetus, & maternal BMI
When should cervical length be measured?
second trimester at 16 weeks transvaginally
- ladies with previous history of preterm labor
- history of mid trimester loss
What is a low lying placenta?
less than 2cm between placental edge & cervical os
- transvaginal evaluation
- recheck it at 32 weeks
How is the amniotic fluid volume measured?
- deepest vertical pole: normally 2 - 8 cm
- amniotic fluid index: normally 10 - 25cm
What is seen using the doppler ultrasound?
- middle cerebral artery -> increased in fetal anemia
- uterine artery doppler -> in fetal growth restriction