OB imaging

Question 1

What is the difference between transabdominal & transvaginal ultrasounds?

Answer 1

Transvaginal
- more sensitive
- empty bladder
- used only before 12 weeks

Transabdominal
- full bladder
- affected by maternal BMI
- used in all trimesters

Question 2

What are the indications for ultrasound in the first trimester?

Answer 2

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

Question 3

What are the indications for ultrasound in the second trimester?

Answer 3

1- anomaly scan
2- growth scan
3- measurement of cervical length

Question 4

What are the indications for ultrasound in the third trimester?

Answer 4

1- growth
2- fetal wellbeing assessment: amniotic fluid volume & doppler ultrasound
3- placental localization (esp cases of antepartum hemorrhage)
4- presentation of delivery

Question 5

When should gestational age be determined?

Answer 5

MAXIMUM by 20 weeks

from 14 weeks & more use HC, BPD, & FL for dating

Question 6

What is the best time for detection of anomalies?

Answer 6

18-21+6 days
detection rate 40-90% at 20 weeks

• depends on type of anomaly, position of fetus, & maternal BMI

Question 7

When should cervical length be measured?

Answer 7

second trimester at 16 weeks transvaginally
- ladies with previous history of preterm labor
- history of mid trimester loss

Question 8

What is a low lying placenta?

Answer 8

less than 2cm between placental edge & cervical os
- transvaginal evaluation
- recheck it at 32 weeks

Question 9

How is the amniotic fluid volume measured?

Answer 9

• deepest vertical pole: normally 2 - 8 cm
• amniotic fluid index: normally 10 - 25cm

Question 10

What is seen using the doppler ultrasound?

Answer 10

• middle cerebral artery -> increased in fetal anemia
• uterine artery doppler -> in fetal growth restriction