Aim of the ultrasound in the first trimestr

• Confirm fetal vitality
• Determine the number of fetuses
• Accurate dating of pregnancy
• Screening for chromosomal aneuploidies
• Early detection of fetal anomalies
• Identification of women at risk of developing preeclampsia
• Assessment of the adnexa 

Accurate dating of pregnancy

• Metods for determining EDD
  • CRL (crown rump length) 
  • LMP (last menstruation period)
  • Date of embryotransfer (in case of ART)

CRL - crown-rump length

• CRL can objectively estimate the gestational age from 8wk or CRL > 10mm
• The accuracy of pregnancy length determination is ± 3 to 5 days
• Limitations: patient’s habitus, correct measurement methodology
• The essential component of combined screening in the first trimestr

  

Why  11+0  and  13+6
 CRL  45-84 mm

• The reason for selecting 11+0
• Screening necessitates the availability of a diagnostic test
• Many major fetal abnormalities can be diagnosed at the NT scan
• The reson for selectiong 13+6
• To provide women with affected fetuses the option of 1st termination
• Nuchal fluid in chromosomally abnormal fetuses decreases after 13 weeks.
• After 13 weeks the fetus becomes vertical 

Nuchal translucency
 

• Nuchal translucency (NT) is the sonographic appearance of a collection of fluid under the skin behind the fetal neck in the first trimester of pregnancy
• The incidence of chromosomal and other abnormalities is related to the size, rather than the appearance of NT.
• 75-80% fetuses with T21 have NT above the 95th percentile

  

Screening for chromosomal aneuploidies

• Depends on maternal age, history and gestational age
• A priori risk is multiplied with the series of LR

  

Fetal heart rate

• In euploid fetuses
  • about 110 bpm at 5 weeks of gestation to 170 bpm at 10 weeks  gradually decreases to 150 bpm by 14 weeks.
• In trisomy 21 
  • mildly increased and is above the 95th centile in about 15% of cases.
• In trisomy 18 
  • mildly decreased and is below the 5th centile in about 15% of cases.
• In trisomy 13 
  • substantially increased and is above the 95th centile in 85% of cases.
• Adding FHR to the combined screening 
  • Is of little signifikance in increasing the DR of T21 and T18 but is essential in increasing the DR of  T13
• Distinguishing between trisomy 18 and 13 
  • Otherwise similar in presenting with increased fetal NT and decreased maternal serum free β-hCG and PAPP-A.

    

Biochemical parametrs

• In trisomy 21 free ß-hCG 
  • is higher than in euploid pregnancies
• In trisomy 21 PAPP-A 
  • is lower than in euploid pregnancies
• First trimestr combined screening for T 21 
  • with a combination of matgernal age, NT, FHR and serum free beta HCG a PAPP-A has a DR od 90% for T 21 with a FPR of 3%

    

Combined screening

• A beneficial consequence of screening for T21 is the early diagnosis of T18 and 13. 
• At a FPR of 3% the DR of  T21 is 90% and of  T18 and 13 is about 95%.

Nasal bone

• The nasal bone is considered to be 
  • present  if it is more echogenic than the overlying skin 
  • absent  if it is either not visible or its echogenicity is the 
    same or less than that of the skin.

• NB improves the performance of combined first trimestr screening increasing the DR of T21 from 90% to 93% and decreasing the FPR from 3% do 2,5%

  

Ductus venosus

• Short vessel connecting the umbilical vein to the inferior vena cava
• 80% of oxygenated blood from the placenta bypasses the liver and is directed to the heart and then to the fetal brain.

• If the ductus venosus a-wave is reversed - detailed ultrasound examination is carried out to exclude or diagnose major cardiac defect
• DV improves the performance of combined first trimestr screening increasing the DR of T21 from 90% to 95% and decreasing the FPR from 3% do 2,5% 

Tricuspid flow

• The fetus should not be moving
• Fetal thorax occupies the whole screen
• An apical four-chamber view of the fetal heart 
• The pulsed Doppler sample… 2 to 3 mm
• The insonation angle less than 30 degrees 
• The tricuspid valve could be insufficient in one or more of its three cusps
• The sweep speed should be high (2 to 3 cm/s)

• Normal profile:
  • with no regurgitation during systole.
• Regurgitation:
  • during approximately half of systole and with a velocity more than 60 cm/s.

Tricuspid regurgitation


At 11-13 weeks tricuspid regurgitation is found ain about:

•  1% Euploid fetuses 
•  55% Fetuses trisomy 21 
•  30% Fetuses trisomy 18 
•  30% Fetuses trisomy 13

Tricuspid regurgitation is more common if: 

• The gestation is 11 than 13 weeks.
• The fetal nuchal translucency is high.

If there is tricuspid regurgitation it is important that detailed ultrasound examination is carried out to diagnose or exclude major cardiac defects.

Tricuspid flow

• Assessment of tricuspid flow improves the performance of combined first trimester screening increasing the DR of T21 from 90% to 95% and decreasing the FPR from 3% do 2,5% 

In the chromosomally abnormal group, about 50% have trisomy 21, 25% have trisomy 18 or 13, 10% have Turner syndrome, 5% have Triploidy and 10% have other chromosomal defects.

Although increased fetal NT thickness is associated with abnormalities and fetal death the majority of babies survive and develop normally.

Management of increased NT > 3,5mm

• Risk for chromosomal defect – invasive diagnostic test
• In case of positive family history – targeted DNA diagnostic
• Detailed morfological ultrasound to exclude defects at 16-22 weeks
• Follow up is normal:
  • risk for serious abnormality or neuro-developmental delay may not be higher than in the general population.

This is found in about 1% of pregnancies.

Persistence of  increased of NT

• No obvious anomaly found on detailed US scan
• Maternal blood should be tested for toxoplasmosis, cytomegalovirus and parvovirus B 19
• Consider testing for certain genetic conditions (Noonan syndrome)
• Follow up scans every 4 weeks

There is a 10% risk of perinatal death or a live birth with a genetic sndrome that could not be diagnosed prenatally.

Simplified cardiac scan - video attached

Holoprosencephaly - video attached
Polydactyly
 - video attached

Congenital diaphragmatic hernia - video attached

Congenital diaphragmatic hernia
 2 - video attached
Pentalogy of Cantrell
 - video attached


HLHS - video attached
HLHS 2 - video attached

Advantages of early anatomy scan

• Longer time for genetic analysis if necessary
• Earlier detection of associated anomalies
• Earlier termination of pregnancy is safer less traumatic
• Especially in cases where there is high risk of structural abnormality due to a history of a previous affected fetus

Limitations of early anatomy scan

• Small size of anatomical structures
• Some defects do not manifest until later in pregnancy
• Increased BMI, fibroids and scars
• Vaginal probe …better resolution
• Fear of false positivity

Mistakes to avoid in the 2nd and 3rd 
trimesters measurement

• There are rules to follow in measurements of fetal biometry (BPD, AC, FL) 
• Small error in pre-viable fetus is not clinically significant
• Errors are more important at extremes
• Optimize the image
• Use correct planes and correct endpoints

BPD measurement

• Head is symmetrically positioned (3rd ventricle, thalami and falx are right in the middle)
• Posterior fossa and orbits should not be on the image
• Cursers are placed correctly (outer to inner) 

AC measurement

• At the level of the liver (the largest abdominal organ in the fetus) 
• Stomach bubble and the intrahepatic umbilical vein
• Skin edge to skin edge
• You can‘t see the skin edge (placenta, oligohydramnios or fetal parts)
• Abdomen is compressed (don´t push so much)
• Too big 
  • measurement is taken in oblique plane, not axial plane 
  • fetus is prone, spine obscures the landmarks
• Too small
  • entire abdominal wall is not included
  • rib is mistaken for skin
  • dependent fat is not included
• When struggling
  • round is best

TG 11,72 mmol/l

FL measurements

• Long axis of the bone parallel to the transducer
• Only diaphysis and metaphysis are measured, epiphysis is excluded
• Not at the longest echogenic point (the „distal femoral point“ which has no anatomic correlate)

Mistakes to avoid in the anatomy - 
lateral ventricles

• Lateral ventricles artificially increased (off axis measurement)
• Inner border of the lateral ventricles
• Dangling choroid (greater then the 3mm space between the wall and choroid)
• Assume symmetry unless asymmetry is visible

  

Choroid plexus cysts

• < 1% of fetuses
• Associated with trisomy 18 (x transient normal finding)
• Discrete round structures, >2mm, completely within the choroid, seen in 3 planes
• Differential is the spongy choroid 

Dandy – Wolker Variant

• Absent or hypoplastic cerebellar vermis
• Vermian development not complete until at least 18 weeks
• Overcalled because
  • fetuses are too young
  • images too oblique (semi-coronal)
• Stay axial to include vermis

  

Mega Cisterna Magna

• Overcalled as pathology
• Look for well formed cerebellum in axial plane
• Note normal subarachnoid septa in cisterna magna
• Careful search for other malformations
• If none, good outcome

Kidneys

• Adrenal glands are labeled as kidneys
• Stomach on image (higher than the level of the kidneys)
• Adrenals are hypoechoic and easy to see
• Kidneys are isoechoic and not easy to see
• Kidneys have a black slit…..renal pelvis 

Pseudo Ascites

• Hypoechogenic rim along the abdominal wall
• Look elsewhere in the pelvis and abdomen

3VT view

• Course and size of PA, Ao and SVC 
• Aortic isthmus and the ductus arteriosus
• Aortic arch right or left-sided 
• Thymus visualised
• Assessment with colour doppler: „Blue V“ or „Red V“
• Atypical vessels (left persistent SVC, vertical vein)

3VT view in early gestation

• Very important view in evaluating great vessels in early gestation 
• Rule out conotruncal anomalies of very serious consequences

Abnormal 3VT view (2D and colour)

• Abnormal vessel size (large or small
• Abnormal vessel number
• Abnormal course and alignment
• Discontinuity of vessels
• Turbulent flow
• Reverse flow

Normal size great vessel - video attached
Abnormal size great vessel - video attached

3VT view - conclusion

• 3VT view and 4CV are the most important ultrasound views in the fetus
• It is easy to obtain - especially in early gestation 
• Anatomic landmarks easy identify and master
• It is affected in most major CHD
• Strong consideration should be given to  incorporation in screening (the effort pays off)