Ultrasound for First Trimester Dating and Screening

Question 1

T1 USS used for

Answer 1

Dating
Identification of multiple pregnancy
Screening for trisomies
Gross anomalies (anencephaly, cystic hygroma)

Question 2

T1 US window

Answer 2

11+3 to 13+6wks

Question 3

What is used to date pregnancy in each stage:

Answer 3

From week 11+3-13+6: Crown-Rump Length (CRL)
expected to be 45-84mm
14-20: Head circumference
>20 measurements are innacurate

Question 4

Combined test

Answer 4

Nuchal translucency
b-hCG
PAPPA
Maternal Age

Question 5

Nuchal translucency median

Answer 5

if CRL 45mm = 1.2mm

id CRL 84mm = 1.9mm

Question 6

Trisomy 21 b-hCG and PAPP-A

Answer 6

High b-hCG

Low PAPP-A

Question 7

% of T21 picked up by combined test

Answer 7

90%

Question 8

Results of combined test

Answer 8

High chance <1:150
Low chance >1:150
Takes 2 weeks max

Question 9

Improved false positives on the combined test

Answer 9

examine nasal bone, ductus venosus flow, and tricuspid flow

Question 10

Quadruple test

Answer 10

weeks 14-20

• alpha-fetoprotein
• hCG
• unconj oestriol
• inhibin A

Question 11

Triple test

Answer 11

some countries
hCG
unconj oestriol
AFP

Question 12

If high risk screening offer invasive testing

Answer 12

CVS: 11-15wk (99%)
Amniocentesis: >15wks (99%)
cffDNA: privately

Question 13

Pregnancy of unknown location

Answer 13

Def: positive test but no IU or EU pregnancy
?ectopic that couldnt be seen on TVUSS
Mx:
repeat hCG at 48hrs
repeat TVUSS
Laparoscopy
most will self resolve