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- General Guidelines And Anatomy Of Obstetrics Ultrasound
(Prince of Wales Hospital)
- Placental Ultrasound
- Ultrasound of the Gut Abnormalities
- Urinary Tract US
- Problems of Liqour Volume
 
General Guidelines And Anatomy Of Obstetrics Ultrasound
(Prince of Wales Hospital)
 
ULTASOUND IN THE FIRST TRIMESTER
   
Day 14 Ovulation occurs
   
Day 20-23 Implantation
   
Week 4 Formation of a primitive uteroplacental circulation
   
Week 5 Formation of a primitive paired vascular system, central nervous system and musculoskeletal system.
   
Week 6-10 Embryonic period
  1. Essentially all adult internal and external structures are formed
  2. Nearly all congenital malformation except abnormalities of the external genitalis originate during this period.
   
Week 8 The heart attains its definitive form
   
Week 10 The GI system has formed and remains herniated into the umbilical cord.
   
Week 12 The intestines return to the fetal abdomen.
 
ESTIMATING GESTATION AGE
 
CRL ( Crown-Rump Length )
 
1. The maximum length of the fetus from head to coccyx excluding the limbs.
2. The most reliable estimate of gestation age between 6-12 weeks.
3. But flexion and extension movement of the fetus can affect the measurement significantly.
     
BPD (Bi-Parietal Diameter)
 
1. The most commonly accepted plane of reference is the one which includes the falx, the thalamus, the cavum septum pellucidum, the third ventricle, the brain stem, the ambient cistern, and an oval head shape.
2. The most reliable estimate of gestation age between 14-20 weeks.
 
   
Femur Length (FL)
 
1. It is the distance measured from the greater trochanter to the lateral condyle of the femur.
2. This measure is correlated well with gestational age during the period of 14-22 weeks.
     
 
 
AC (Abdominal Circumference)
 
1. The junction of the umbilical vein and the left portal vein appears as an echolucent structure that is shaped like a hockey stick. This junction serves as the landmark for the level at which the abdominal circumference is obtained.
2. It is important not to confuse the gall bladder with the umbilical vein, because the long axes of both these structures lie in the same plane..
3. The stomach serves as the alternative landmark for AC in those situations where the fetal spine is directly anterior to and shadowing the umbilical vein..
 
 
AC (Abdominal Circumference)
 
1. Gestational Sac
  - It can be identified consistently as early as 5 post-menstrual weeks.
2. Fetal Pole.
  - It can be first seen at week 6 with heart activity.
3. Yolk Sac.
  - It can be seen between weeks 7-11..
  - It is the site of early blood formation and forms the luminal GI tract.
  - It appears as a round cystic structure which is separate from the fetal pole.
4. Fetal Thorax.
  - The heart can be recognized as a fluid-filled structure within the fetal thorax.
  - The lung has similar echogenicity to other soft tissue organs such as the liver or spleen.
 
   
5. Fetal Abdomen
  - The structures that are most often imaged include the fetal stomach, liver, umbilical vein, kidneys, bladder and adrenal
 
 
6. Genitalia and Cord
  - The demonstration of 1A1V is associated with numerous fetal congenital anomalies including serious cardiovascular and genitourinary abnormalities. 1A is also associated with diabetes, twins and increased neonatal mortality.