The Early Gestation Scan

1
The Early Gestation Scan
2
Embryonic/fetal growth 1st trimester

• Crown rump length best index of gestational
  length
• Phase of most rapid growth in length (up to first
  ½ preg.)
• Time when growth influenced most by
• genome aneuploidy
• external influences infection
• drugs
• Stage being set for later effects smoking
• maternal nutrition
• uterine circulation

3
ROUTINE EARLY ULTRASOUND (Cochrane Library)
earlier detection of multiple pregnancies twins
undiagnosed at 26 weeks OR 0.08, 95 C I 0.04 to
0.16 reduced induction post-term pregnancy
O R 0.61, 95 C I 0.52 to 0.72 No differences
detected for substantive clinical outcomes
perinatal mortality O R 0.86, 95 C I 0.67
to 1.12 Where detection of fetal abnormality
was a specific aim number of terminations of
pregnancy for fetal anomaly increased.

4

• Uterus
• Endometrial decidual reaction
• Gestational sac
• Position
• Size
• Shape
• Yolk sac
• Fetal pole- measure crown rump length
• Cardiac activity
• Adnexae
• Corpus luteum
• Free fluid

5
MSDgt 2cm and no fetal pole visible likely
anembryonic pregnancy
Two vertical measurements same diameter,
therefore, 2 horizontal and 1 vertical added and
divided by 3 to give MSD
6
Fetal pole gt6mm and no cardiac activity seen
likely non-viable pregnancy
7
Gestational dating

• CRL BEST measurement
• Fetus in longest axis
• Fetus not curled up
• Measurement from rump to top of head
• CRL until 12 weeks
• BPD after 15 weeks
• 13- 15 weeks ? Wait until 15 weeks
• Give an EDD on report using obstetric calculator
• DO NOT CHANGE DATES IF CRL OR EARLY BPD

8
(No Transcript)
9
(No Transcript)
10
Ultrasound allows us to determine the
CHORIONICITYthat is the membrane set up
11
CHORIONICITYan important 1st trimester diagnosis

• Discordant nuchal translucency in MC twins -40
  risk TTTS
• MC twins-10X morbidity mortality of DC
• Intertwin transfusion - a normal event-10-15MC
• Complications- acute TTTS after fetal death
  - chronic TTTS
• - acardiac(TRAP)
• (high incidence of antenatally acquired cerebral
  lesions)

12
Chorionicity

• Monochorionic Diamniotic (MCDA)
• One placenta
• Thin membrane
• T shaped insertion
• Same sex
• One chorion, 2 amnions (visible early)
• Dichorionic Diamniotic (DCDA)
• One or two placentae
• Twin peak or Lambda sign

13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
What sort of twins?
18
Extra Special Problems of Monochorionic Twins

• Monoamniotic twins (1 of MCs)
• TRAP
• Congenital anomaly in 1
• Conjoined twins
• Nb can get TTTS

19
PLACENTAL ANASTOMOSES

• A-A
• A-V
• V-V
• TTTS associated with absence of AAA
• isolated A-V seem to be implicated

20
ACUTE TTTS

• Occurs when 1 dies
• in 25 2nd twin dies soon after
• in 25 - 40 ? neurological sequelae
• Treatment
• i) prevention
• ii) delivery - viability

21
Twin To Twin Transfusion Syndrome
U/S for prediction diagnosis and management
22
(No Transcript)