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The Early Gestation Scan - PowerPoint PPT Presentation
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The Early Gestation Scan. Embryonic/fetal growth 1 st 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
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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
genomeaneuploidy
external influences infection
drugs
Stage being set for later effects smoking
maternal nutrition
uterine circulation
(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.
Uterus
- Endometrial decidual reaction
- Gestational sac
- Position
- Size
- Shape
- Yolk sac
- Fetal pole- measure crown rump length
- Cardiac activity
- Adnexae
- Corpus luteum
- Free fluid
MSD> 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
Fetal pole >6mm and no cardiac activity seen =likely non-viable pregnancy
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
Ultrasound allows us to determine the CHORIONICITYthat is the “membrane set up”
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-10-15%MC
- Complications- acute TTTS after fetal death - chronic TTTS
- acardiac(TRAP)
(high incidence of antenatally acquired cerebral lesions)
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
Extra Special Problems of Monochorionic Twins
- Monoamniotic twins (1% of MCs)
- TRAP
- Congenital anomaly in 1
- Conjoined twins
- Nb can get TTTS
PLACENTAL ANASTOMOSES
- A-A
- A-V
- V-V
- TTTS associated with absence of AAA
- isolated A-V seem to be implicated
ACUTE TTTS
- Occurs when 1 dies
- in 25% 2nd twin dies soon after
- in 25 - 40% neurological sequelae
Treatment
i) prevention
ii) delivery - “viability”
Twin To Twin Transfusion Syndrome
U/S for prediction diagnosis and management
