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The Early Gestation Scan

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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The Early Gestation Scan

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  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 genomeaneuploidy 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. 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

  6. Fetal pole >6mm 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. Ultrasound allows us to determine the CHORIONICITYthat is the “membrane set up”

  9. 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)

  10. 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

  11. What sort of twins?

  12. Extra Special Problems of Monochorionic Twins • Monoamniotic twins (1% of MCs) • TRAP • Congenital anomaly in 1 • Conjoined twins • Nb can get TTTS

  13. PLACENTAL ANASTOMOSES • A-A • A-V • V-V • TTTS associated with absence of AAA • isolated A-V seem to be implicated

  14. ACUTE TTTS • Occurs when 1 dies • in 25% 2nd twin dies soon after • in 25 - 40%  neurological sequelae Treatment i) prevention ii) delivery - “viability”

  15. Twin To Twin Transfusion Syndrome U/S for prediction diagnosis and management

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