Ultrasound in Obstetrics Flashcards
What is an Obstetric Ultrasound
Obstetric Ultrasound is the use of ultrasound scans in pregnancy
What is the name of the equipment used in ultrasund scans
Real-Time Scanners
Explain briefly how Real time scanners work
Sound waves are emitted from a transducer that is placed in contact with the maternal abdomen
It is moved around to look at any particular content of the uterus
What is a requirement for an ultrasound in early pregnancy
full bladder
What are the 7 main uses of ultrasonography
- Diagnosis and confirmation of early pregnancy
- Vaginal bleed during early pregnancy
- Determination of gestational age and fetal size
- Detection of abnormalities
- Polyhydramnios and Oligohydramnios
- Multiple Pregnancies
- Placental localization
The gestational sac can be visualized as early as which week
4 1/2 weeks
When can the yolksac be observed
5 weeks
When can the embryo be observed and measured
5 1/2 weeks
What is the normal heart rate at 6 weeks
90-110 bpm
What is the normal heart rate at 9 weeks
140-170 bpm
How is the diagnosis of a missed abortion usually made
by serial ultrasound scans demonstrating lack of gestational development
if ultrasound demonstrates a 7mm embryo but cannot demonstrate a clearcut heartbeat, a missed abortion may be diagnosed
What are the five standard biometric parameters to estimate gestational age and /or foetal weight
Crown Rump Length (CRL) Biparietal Diameter (BPD) Head Circumference Abdominal Circumference (AC) Femur Legth (FL)
When should the Crown-Rump measurement be made
Between 7-13 weeks
Which biometric parameter to estimate gestational age and/or fetal weight is best studied and highly reproducible
Biparietal Diameter
BPD can be used to predit gestational age when measured between which weeks of pregnancy
14-20
BPD can be used to predict gestational age within what range
+/-7 days
What is the plane that both the BPD and Head Circumference are measured on
Measured on a plane of section that intersect the thalami and the third ventricle
Which is the single most important measurement in late pregnancy
Abdominal Circumference
Why is abdominal circumference the most important measurement in late pregnancy
serial measurements useful in monitoring growth
What is the “Femur Length” used to measure
Measures the longest bone in the body and reflects the longitudinal growth of the fetus
The femur increases from what length at 14 weeks to what length at term
1.5cm at 14 weeks to 7.8 cm at term
What is nuchal translucency?
It is a term used to describe sonographic appearance of a collection of fluid under the skin behind the fetal neck at 11-13 weeks of pregnancy
What abnormalities can Nuchal Transluceny detect?
Down’s Syndrome
Trisomy 21
Structural abnormalities in the foetus can be detected by which week of pregnancy
Week 20
List 2 soft markers for chromosomal abnormalities in the first trimester
- Absence of foetal nasal bone (Cleft Palate)
- An increased foetal nuchal translucency (Downs’ Syndrome)
Disitinguish between hydramnios and oligohydramnios
Polyhydramnios is excessive amniotic fluid while oligohydramnios is a decreased amount of amniotic fluid
Which scan is considered indispensible in early diagnosis of ectopic pregnancy
Transvaginal Scan
How is doppler frequency obtained?
From the phase shift
T2(time of returned signal)- T1(time of omitted signal)
How is Doppler Frequency obtained?
It is obtained by measuring the time difference for the signal to be returned when reflected from moving scatters
Doppler Ultrasound is most widely employed in the detection of
Fetal Cardiac Pulsations
What are the two routes of doppler examinations
Abdominal
Transvaginal
What is the name of the handheld device that is commonly used to detect fetal heartbeat
Doptone
Doppler Flow Velocity Waveforms are used to assess
Blood Flow Characteristics in foetal blood vessels
Describe the appearance of Umbilical Artery flow in the Doppler
Saw-tooth appearance of arterial flow in one direction and continuous umbilical venous flow in the other
reversed Diastolic velocity (REDV) can be seen in
Severe Intrauterine Growth Restriction
True of False
Volume flow in the Umbilical Arteries increases with advancing gestation
True
Which method is particularly indispensible in the diagnosis and assessment of congenital heart abnormalities
Colour Flow Mapping
What is the difference between power doppler and Doppler Flow Velocity
Power Doppler does not use flow velocity information to visualize slow flow in smaller blood vessels
What is one disadvantage of Power Doppler
It does not display flow direction or different velocities
List four advantages of 3D scans
-Impressive to parents
- Increasing psychological bonding between the parents and the baby
- More accurate volumetric measurements
- the presence or absence of abnormalities are better appreciated
Which ultrasound technique is used to detect more subtle features: low set ears, facial dysmorphia, clubbing of feet
3D Ultrasound
The ability to obtain a good 3D picture depends on what variables
operator skill, amount of liquor (amniotic fluid)
foetal position
maternal obesity
When is the first scan generally booked in pregnancy
7 weeks
What is the aim of the first scan?
To detect:
-congenital malformations
-exclude multiple pregnancies
-verify dates and growth
-determine placental position
When is the second scan done
18-20 weeks
What is the aim of the second scan
To detect congenital malformations
Exclude multiple pregnancies
Verify Dates and Growth
Determine Placental position
When is the 3rd scan doen
week 34
What is the aim of the third scan
-evaluate foetal size
-assess foetal growth
