The Early Gestation Scan

Embryonic/fetal growth 1 st trimester Crown rump lengthbest index of gestational lengthCrown rump lengthbest index of gestational length Phase of most rapid growth in length (up to first ½ preg.) Time when growth influenced most by aneuploidy genomeaneuploidy external influencesinfection drugs Stage being set for later effects smoking maternal nutrition maternal nutrition uterine circulation uterine circulation

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.

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 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 CHORIONICITY that is the “membrane set up”

CHORIONICITY an 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 %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

What sort of twins?

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 %  neurological sequelae Treatment i)prevention ii)delivery - “viability”

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