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Ultrasound in obstetrics (US 11+0 to 13+6 (markers of chromosomal…
Ultrasound in obstetrics
US 11+0 to 13+6
- number of fetuses in uterine cavity
- assesment of fetal hesrt rate (FHR),
- Biometry measurment : crown-rump length (CRL), biparietal diameter (BPD),
- assesment of fetal anatomy:
head – shape, falx cerebri, choroid plexus,
abdominal walls – umbilical cord insertion, stomach,
fetal heart – lokalization, axis and heart rate,
urinary bladder, spine, upper and lower extremities,
chorionicity of multiple pregnancies -
LAMBDA sign for DCDA – DiChorionic DiAmniotic),
T sign for MCDA – MonoChorionic DiAmniotic.
Assesment of risk of the most frequent chromosomal abnormalities ( trisomy 21, 18,13)
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Rules of NT measurement
a. Image enlargement
– head and 1/3 of fetal thorax;
b. Neutral head position – no excessive flextion or deflexion;
c. Fetal position
– median sagittal section;
e. the widest diameter, calipers „from inner to inner” border, transverse arm of the caliper paralel to the skin
USG 18.-22. t.c.
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- Biometry, - assesment of fetal weight and GA (gestational age)– biometric measurments:
BPD – Bi-Parietal Diameter,
HC – Head Circumference,
AC – Abdominal Circumference,
FL – Femur Length
USG 28.-32. GA.
- Examination of organs and wellbeing of the foetus with doppler flows.
- Main vessels that have to be assesed are::
Middle cerebral artery (MCA)
Umbilical artery (UmA)
Ductus venosus (DV)
Umbilical Vein (UmV)
Left and right uterine artery (RUA, LUA)
- Screening for fetal malformations
- we should follow ALARA rule (As Low As Reasonably Achievable) and perform the scan in the shortest time and with minimal exposition allowing to complete the procedure
Hardware requirements
- 2 types of probes:
transabdominal convex
with frequency 3.5-5.0 MHz,
transvaginal convex (sector)
with frequency 4.0-7.5 MHz;
US scan before 10 weeks
- It should be performed with the transvaginal probe.
- Purpose:
a.visualization of gestational sac (GS) – confirmation of intrauterine gestation and exclusion of ectopic pregnancy,
b.measurement (GS – average of 3 measurements), localisation, shape (round, oval, irregular) of gestational sac, number of gesational sacs,
c.assessment of the fetus – presence, CRL measurement, presence of FHR
d.assessment of the numer of fetuses, chorions and amnions,
e. assessment of the yolk sac (YS)
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