OBS imaging Flashcards
What is the most accurate way of dating a pregnancy?
CRL between 7 -12 weeks
What is the accuracy of CRL to predict the date of delivery?
+/- 5 days
+/- 3-8 days in another guideline
Why is accurate dating of pregnancies important (4)?
Decreases # of IOL
Helps in scheduling CS
Assessment of fetal growth
Better accuracy of aneuploidy screen
Of parameters for EFW in the second trimester, which is the most accurate?
Which has the most variation?
Most accurate: Head circumference
Most variation: Abdo circumference
What is the incidence of ectopic pregnancies ?
What is the % of fetal death related to ectopic pregnancies?
Incidence 1%
Maternal death 4%
At how many weeks can midgut herniation be considered abnormal
12 weeks
What is the highest value normal value of NT at 11-14 weeks?
What size should be the CRL to use the NT?
3.5 mm
45 - 84 mm
What is increased NT related to?
Trisomy 13, 18, 21
Chromosomal or developmental abnormalities
Genetic syndroms
What are the parameters of the algorithm to predict maternal PET?
Maternal clinical factors
MAP
Bilateral uterine artery pulsatility index
PAPPA
Placental growth factor
What are US findings suggestive of early pregnancy loss (4)?
Bradycardia (< 85 bpm) > 7 weeks
Small sac relative to the embryo (GS - CRL < 5 mm)
Enlarged or abnormal yolk sac (> 5-6 mm)
Subchorionic hematoma
What is the single most useful test to differentiate a viable from a non-viable pregnancy?
Progesterone level
< 20 nmol
Sensitivity 75 %, specificity 98% for failed pregnancy
What is the single most useful test to differentiate an IUP from an ectopic?
US
What are the US criteria to diagnose an arrested pregnancy?
CRL >/= 7 mm and no FHR
Empty GS with GSD >/= 25 mm
No cardiac activity 2 weeks after an US showing a GS without a yolk sac
No cardiac activity 11 days after an US showing a GS with a yolk sac
What is the first test to do in a patient with suspected ectopic?
serum beta hCG!
What is the time frame of the gestational period?
8 weeks after conception
10 weeks after LMP
What is the incidence of heterotopic pregnancies in spontaneous and ART pregnancies?
Spontaneous: 1/7000 - 1/30 000
ART: up to 1%
What are the minimum requirements to diagnose an IUP on US?
Intra uterine GS + (embryo or yolk sac)
What is the most common location of ectopic pregnancies?
1 - Ampulla (70%)
2- Isthmic (12%)
3- Fimbria (11%)
4- Ovarian (3%)
5- Interstitial / cornual (2-3%)
6- Abdominal (1%)
7- Cervical (<1%)
What is the minimal rise in beta-hCG in viable pregnancies?
55% in 48h
(1.4 - 2.1) in 48h
When does beta hCG first become positive?
21 -22 days after LMP
8 days after ovulation
= Start of implantation
What is the time frame of the gestational period?
8 weeks after conception
10 weeks after LMP
When does the amnio fuse to the chorion?
12 - 16 weeks of gestation
Describe the variations in FHR between 5-10 wks
5.5 - 6.5 weeks < 100 bpm
7-10 wks - up to 180 bpm
How long does sperm survive?
5-7 days
When can you first hear FHR by doptone?
11 -12 weeks
When should the CRL be used (in mm) to date a pregnancy?
Between 10 - 84 mm
10 mm = 7 weeks
Between how many weeks gestation are CRL and BPD equivalent?
12 - 14 weeks
What is the definition of dolichocephaly
Head longer than expected
What is the definition of brachycephaly
Skull shorter than expected
What is achodroplasia?
Prevents ossification of long bones.
Dwarfism
Scoliosis
Macrocephaly
What parameter of biometry correlates better with GA?
HC
Which biometry parameter has the most variation?
AC
What are some advantages of doing a dating US
- Improve MMS accuracy
- Identification of gross anomalies
- Identification of twin gestations
- NT
- DEcrease post date inductions
