Imaging technique of USG in first trimester pregnancy

1. USG IN OB & GY
Ref- Ultrasound in Obstetrics and Gynecology
A practical approach
First edition
Editor- Alfred Abuhamad, MD

3. USG IN FIRST TRIMESTER
• Location
• Confirmation of intrauterine gestation
• Assess viability
• Number
• Date
• Major fetal anomalies

4. GESTATIONAL SAC
• Paracentrically in the decidua = intradecidual sac sign
• Should not be confused with fluid collection between
the decidual layers= pseudosac ( especially in the
presence of an ectopic pregnancy)
• Growth rate 1 mm/day
• Echogenic border appears when mean diameter 2-4
mm
• Echogenic border is important USG sign

5. GESTATIONAL SAC
• MSD cut off of ≥25 mm with no embryo = failed
pregnancy
• MSD between 16-24 mm with no embryo= suspicious
of failed pregnancy

6. Fluid collection

7. MSD ≥ 25 mm without embryo

8. YOLK SAC
• Yolk sac –at 5 week with TVS
• 2 mm at 6 wk
• 6 mm at 12 wk
Suspicious
Less than 3 mm bet 6-10
wk
More than 7 mm before 9
wk

9. Normal yolk sac
Diamond engagement ring
Abnormal yolk sac
A- small B -large

10. AMNION
• Amniotic sac appears following the appearance of the
yolk sac and just before the appearance of the
embryo
• Growth rate of embryo closely related to that of
embryo bet 6-10 wks
1
2
3
1- yolk sac
2- Vitelline duct
3-amniotic sac

11. EMBRYO
• First focal thickening of yolk sac= diamond
engagement ring
• First cardiac activity – 5-7 mm in length or greater
• 100-115 BPM before 6 wk
• 145-170 at 8 wk
• 137 to 144 after 9 wk
• Increased 1 mm per day in length

12. EMBRYO - CRL
• Length of the embryo- CRL ( crown rump length) (
mm)
• Cranial to caudal end of the body
• Cutoff of ≥ 7 mm with no cardiac activity = failed preg

13. EMBRYO
• Embryo develop within the amniotic cavity ( intra-
amniotic)
• Yolk sac is out side the amniotic cavity ( extra
amniotic)
• 6 wk- grain of rice appearance
• Age advance – gummy-bear appearance
• TVS at 12 wk or beyond – for diagnosis of major
malformation

14. MULTIPLE GESTATION
• 1st trimester is most optimum time for dx of multiple
gestations & chorionicity
• One placenta = monochorionic ( MC)
• Two separate placenta = dichorionic ( DC)

15. MULTIPLE GESTATION
• All dichorionic placenta , by definition, have 2
amniotic sacs
• Dizygotic twins always have – dichorionic placentation
• Dizygotic twins are more common tan monozygotic
• Monozygotic twins
• monochorionic & diamniotic (75%)
• Dichorionic & diamniotic (25%)
• Monochorionic & monoamniotic (1%)

16. MULTIPLE GESTATION
DICHORIONIC – DIAMNIOTIC TWINS
• Two gestational sac
• Thick dividing membrane
• Delta, lambda or twin peal sign ( dichorionic
gestation)

17. MULTIPLE GESTATION
MONOCHORIONIC – DIAMNIOTIC TWINS
• One gestational sac & two amniotic sac
• Dividing membrane – thin and inserts in T
configuration into shared placenta

18. MULTIPLE GESTATION
MONOCHORIONIC – MONOAMNIOTIC
TWINS
• One gestational sac and one amniotic sac
• No separating membrane
• Conjoined twins ( mono – mono)

19. DATING IN THE FIRST TRIMESTER
• Gestational sac diameter when no embryo is seen
• CRL in late 1st trimester 912-13 wk)
• BPD
• Measuring before 14 wks is most reliable for
gestational age

20. BIOMETRIC MEASUREMENTS IN FIRST
TRIMESTER
CRL
• Less than 14 wk use CRL
• Mid sagittal plane
• Longest straight line distance from the top of head to
rump
• Increased 1.1 mm per day
• GA = CRL(mm)+ 42

21. BIOMETRIC MEASUREMENTS IN FIRST
TRIMESTER
MSD
• First visualized – 4 to 4.5 wk after LMP
• Best by TVS
• Paracentrically with echogenic borders
• Calculated as mean diameters from its greatest
sagittal , transverse and coronal diameter
• Confirm intrauterine preg but not viability
• Empty G sac or with yolk sac – 5- 6 wk gestation
• Follow in 7- 14 days – presence of an embryo –
confirm viability

22. BIOMETRIC MEASUREMENTS IN FIRST
TRIMESTER
MSD

23. AMNIOTIC SAC / YOLK SAC
• Amniotic sac – thin membrane , less echogenic than
yolk sac
• Size of amniotic cavity or yolk sac – not for dating but
for documentation of normal development

24. ELEMENTS OF PREGNANCY FAILURE
• UCG (+) , no G sac in USG
• DDx- incomplete abortion
• Ectopic pregnancy
• Early intrauterine preg that is not yet recognizable
• G sac by TVS , no embryo or yolk sac
• Embryo by TVS , no cardiac activity
• Embryo with cardiac activity but measurements are
out of range
• Abnormal anatomic appearance of embryo

25. ELEMENTS OF PREGNANCY FAILURE
• If pt is not in danger ( bleeding , pain) – ectopic is not
in DDx but follow up USG is helpful
• G sac no noticeable change after 1 wk or more –
suspected failed pregnancy
• Subchorionic hge without other markers of pregnancy
failure – good outcome

26. DX SIGNS OF EARLY PREG FAILURE IN
1ST TRIMESTER
• CRL ≥7 mm without cardiac activity
• MSD ≥25 mm without embryo
• G sac with yolk sac but no embryo at 2 or more wks
follow up scan
• Embryo without heart beat at 11 days or more after
USG showed G sac with yolk sac

27. THANKS
PP BY DOUBLE M
14-APR-2019
HAPPY MYANMAR WATER FESTIVAL