2nd trimester normal
Do not be overwhelmed
By dividing the examination into anatomical regions, the scan is easier to manage.
- Head
- Thorax
- Heart
- Abdomen
- Spine
- Limbs
Of course, these are scans of opportunity where we must obtain the views based on the foetal lie and cannot simply follow a sequence as we would for other ultrasound examinations.
Fetal Head
Measure:
- Bi parietal Diameter (BPD) and Head Circumference (HC)
- Lateral ventricle in the posterior portion inner to inner wall
- Cerebellum
- Cisterna magna
- Nuchal fold
Assess:
- Head shape and skull bones
- Intracranial symmetry (thalami, Cavum septum pellucidum (CSP), cerebrum, ventricles)
- Choroid plexus
- Corpus callosum
- Profile (mandible, forehead and nasal bone)
- Face (symmetry, nostrils, lips, lenses)
Biparietal diameter (BPD and Head circumference (HC)
This is an axial cross section of the fetal head obtained at the level of the thalami and cavum septum pellucidum. The image should show the falx in a horizontal position with both parietal bones equidistant to the midline to ensure symmetry before measuring.
The shape of the head should be oval with sutures present.
The correct plane for the measurement of the head circumference (HC) and bi-parietal diameter (BPD)must include the cavum septi pellucidi, thalamus and choroid plexus in the atrium of the lateral ventricles.
Ultrasound image
BPD: Measure outer table of the skull to the inner table.
HC: Measure around the outer table of the skull.
The cerebellar diameter should approximately equal the weeks of gestation. (EG 19weeks=19mm). It should be a dumbbell shape.
Normal cisterna magna is less than 10mm but not absent (obliterated).
A normal nuchal fold is less than 6mm (between 17-20weeks).
Ultrasound image-
The LATERAL VENTRICLES should be less than 10mm in diameter from inner wall to inner wall at right angles to the falx (best measured at the level of the glomus in the posterior horn).
The CHOROID PLEXI should be homogeneous. Small, and sometimes multiple, choroid plexus cysts are a common finding on high resolution equipment. They are of doubtful significance as an isolated finding.
PROFILE – should be imaged in a mid sagittal plane with the angle of the face at approximately 45degrees. The level of calcification and the full length of the nasal bone should be noted as a hypoplastic nasal bone is associated with trisomy 21 (Down Syndrome). There should be no frontal bossing (sloping) of the forehead. The tip of the mandible, upper and lower lips and tip of the nose should be in line, otherwise micrognathia should be suspected.
Ultrasound image ORBITS AND FACE: Ensure there is symmetry with a normal inter-orbital distance.
Ultrasound image
NOSE & LIPS: From the ‘face’ image, rotate the probe to visualise the nose and lips front on in a coronal plane.
Two distinctly separate nostrils with an echogenic underlying band and an intact hypoechoic upper lip should be seen.
A coronal nose and lips view.
The lenses of the eyes can be viewed in bo th the axial and coronal views.
This is an axial view of the mandible. It is important to visualise it in its entirety.
The palate must be shown in an anterior axial view to ensure that it is intact without any linear defects from the outer to inner bony margins and soft tissues. These may or may not coincide with a cleft lip.
This view must include the maxilla with alveolar ridge, tooth buds, maxilla palatine process, transverse palatine sutures, posterior nasal spine and pterygoid process.
Corpus callosum
The visualisation of the corpus callosum in a sagittal view has become a standard part of a morphology scan. Suspicion of its absence (agenesis of the corpus callosum) should be aroused if the cavum septi pellucidi cannot be seen.
The corpus callosum begins to arise embryologically at 13 weeks, however it often the most posterior portion, the splenium, may not be fully developed at the time of the morphology scan (ideally 20 weeks) . Careful assessment of the posterior splenium portion is warranted to detect partial agenesis or hypoplasia.
Partial agenesis of the corpus callosum results from an arrest of growth which occurs between 12 and 18 weeks of gestation and usually involves the dorsal part or splenium, with the more anterior callosal segments being preserved.
This is a B mode image of the corpus callosum. It is identified by viewing it in a sagittal plane through the frontal bone. By obtaining a profile image and moving the probe to insonate from a perpendicular plane to the superior portion of the baby’s head , good visualisation of the entire corpus callosum can be imaged.
The corpus callosal artery is identified branching from the anterior cerebral artery.
Fetal thorax
Assess:
- Shape and size similar, but slightly smaller relative to the abdomen.
- Diaphragms (left and right) intact.
- Heart located in the chest. Occupying 1/3 of the thorax and angled approximately 45degrees to the left.
- Lungs are isoechoic or slightly echogenic relative to the liver.
The lungs are slightly more echogenic than the abdominal structures..
This image highlights a normal position and heart size in the thorax. Pericardial and pleural fluid, cysts or lesions should be excluded.
Fetal Heart
Fetal Abdomen
Measure:
- Abdominal circumference
- Renal pelves (measured in a transverse plane)
Assess:
- Situs (stomach and heart on foetal left)
- Stomach
- Cord insertion
- Kidneys
- Bladder
- Liver
- Spleen
- Bowel (in particular the echogenicity as increased echogenicity may be related to cystic fibrosis)
Abdominal Circumference (AC)
The Abdominal Circumference must include the portal section from the umbilical vein, the stomach and a true cross section of the spine with 3 ossification centres. It should be circular in shape.
Note that the portal vein should be seen coursing towards the liver. Ensure there is not a persistent Right umbilical vein.
Ultrasound image –
Note that the portal vein should be seen coursing towards the liver. Ensure there is not a persistent Right umbilical vein.
Ultrasound image- First, confirm that the organs are correctly sited right vs left.
An axial plane through the chest and upper abdomen shows the heart and stomach on the same side (which has been proven to be the left).
Ultrasound in a coronal plane, confirm the presence and position of heart, stomach and bladder. Also check the diaphragm.Ensure that there is no herniation of abdominal contents into the thorax.
Fetal kidneys
Ultrasound to confirm the presence and position of both kidneys. Be cautious not to mistake the adrenal glands which are quite large. Look for the anechoic renal pelvis. The renal pelvis measured in a transverse view should be less than 5mm.
The kidneys may be measured in a sagittal or coronal ultrasound plane. Utilise colour/power doppler to confirm renal arteries and help identify the kidneys in a larger patient. Narrowing the dynamic range is also useful in improving recognition in technically dificult examinations.
Umbilical cord
Umbilical cord insertion ultrasound image.
Ensure the abdominal wall around the cord insertion is intact and that no abdominal contents have herniated into the cord.
Use power/colour doppler to confirm the presence of 2 umbilical arteries forking around the bladder. (Be careful not to slip into a more coronal plane and mistake the iliac arteries.)
Ultrasound image. There is an obvious penis identified at 18-20 weeks. Shown on the mouseover is the 3 parallel white stripes of the external genitalia of the female vulva.
Fetal Spine
Assess:
- From skull base to distal sacrum
- For presence and symmetry of the ossification centres and the posterior skin edge intact.
Evaluate in 3 planes:
- Sagittal
- Coronal
- Axial
Ultrasound Image
Sagittal Spine.
Ensure there is a uniform, intact posterior skin edge.
Ultrasound Image
Coronal Spine.
Check for any scoliosis.
Cervico-thoracic spine:Check the ribs for symmetry.
Lumbar/sacral spine: In coronal, visualise the sacral taper and pelvic bones.
Ultrasound Image
Transverse Spine.
The 3 ossification centres of the spine should be visible from neck to the lumbo-sacral junction. A smooth intact skin line should be visible throughout.
Beware overlying cord mimicking a meningocoele.
Fetal Limbs
Measure:
- Femur length
- Humeral length (depending on departmental protocol)
- Charts are available for all long bones if needed and should be used if the femoral and humeral lengths are both <10th percentiles.
Assess:
- 12 long bones (Straight, equi-distant to each side and intact)
- 2 feet with 10 toes
- 2 hands with 10 fingers
- 4 limbs seen flexing/extending
Femur Length
The Femur length should only be measured when the femur is horizontal (ultrasound beam is perpendicular) and shadows evenly- at least from both ends.
Ultrasound Image Lower limbs
Confirm the presence and equal size of the tibia and fibula bilaterally.
The foot should only be seen as a rounded area at the base of the leg when seen front on. If you can see the tibia, fibula and foot in one plane, suspect talipes. Rotate 90degrees to see the sole of the foot and the toes.
5 toes should be visualised next to each other and not overlapping.
Ultrasound Image Upper limbs.
Similar to the leg, confirm the presence and size of length of the 3 long bones in each arm.
The fist is often clenched in the ultrasound image. Ideally watch the hand open/close and check for 5 fingers/knuckles on each side. Check for the presence of the 5th middle phalanx. This image is dualled with the thumb in one view separate to the 4 fingers.
SCAN PROTOCOL
Role of Ultrasound
In the 2nd trimester, ultrasound is essential for assessing the:
- Current viability
- Structural integrity of the fetus
- Placental position and condition
This scan must not be done before 18weeks,
20 weeks is optimal.
Patient History
- Gravidity
- Parity (Miscarriage, T.O.P)
- Fertility treatment
- Date of Last Menstrual Period
- Current pregnancy history
- Past pregnancy History (eg gestational diabetes)
- Gynaecological History
- Medication
- Family History if relevant
Limitations
- Fibroids or large maternal body habitus can impede good visualisation of the fetus.
- To ensure the anatomical structures can be visualised a morphology scan is ideally performed at 19 weeks or greater.
Patient Preparation
There is no need to unnecessarily fill the patients’ bladder as the cervix should be assessed using a transvaginal approach and the baby can be visualised without a full bladder.
TIPS AND PITFALLS
- Do not panic. If you do, you will be adding on another 30minutes to the scan time as you and mother get flustered.
- Wait till the baby moves into the required position,do not take short cuts.
- You may even have to bring the Mother in and out of the room 5 times or the next day if after a walk and something sweet to eat the baby still does not cooperate.That is okay!
- Remember you will need to heel and toe the probe to get the correct plane
- Roll the patient and scan them decubitus if it helps, particularly patients with a high BMI
- Show the mother the heart beat initially to calm her from the beginning. Do a 5 minute scan looking over the baby to check the main body parts are present and the situs of the heart and stomach are correct before attempting to start imaging. This is so you are not surprised to find a major defect such as an omphalocele half way through the scan. You will be prepared. Assess the baby’s head first then move down to the heart, abdomen and then the limbs. Look at the placenta and the cervix when all possible imging of the fetus is exhausted, this will give the baby time to move.
Have your worksheet with you and mark off as you go so you will not forget anything.
WHAT TO CHECK WHEN BABY IS SUPINE
- Profile, corpus callosum, nasal bone,nose/lips,mandible,palate,orbits,lenses.
- Humerus,rad/ulna,hands,fingers, phalanges
- Heart,4chamber,LVOT,RVOT, 3VV, arrowhead,heart beat,arches (ductal and aortic)
- Chest cavity
- Diaphragms
- Cord insertion
- 2 umbilical arteries
- Bladder
- Gender
WHEN BABY IS DECUBITUS
- Head,BPD,HC,CBM,NSF,CM,Ventricles, choroids
- Heart,IVS/IAS,LVOT,RVOT, 3VV, Arrowhead
- Diaphragm,liver,GB,bowel
- AC measurement,stomach,umbilical vein, liver,spleen
- Spine coronal,trans
- FL,femora,tib/fib,feet,toes
WHEN BABY IS LYING PRONE
- Spine,skin line,sagittal,trans
- Aortic Arch,Ductal Arch
- Kidneys,long and trans,PUJ
- Diaphragm
- Head, choroids
CERVIX
- Examine with some fluid in the bladder.
- Gold standard is to perform a transvaginal scan as it is the most accurate for measuring and determining if there is any funnelling or Vasa Previa.
- Previous Caesar scar and myometrial thickness, looking for signs of placenta accreta.
PLACENTA
- Anterior, posterior, fundal or lateral
- Placental praevia (or low lying if less than 2cm from internal os)
- Cord insertion
- Fibroids
- Perfusion in all areas of the placenta
OTHER
- Maternal adnexae and ovaries
- Maternal kidneys if mother has had pain there
- Maternal Gallbladder if mother has had RUQ pain.
Equipment setup
- Modern ultrasound unit
- Curved linear probe approx 3-9 MHz depending upon maternal factors
- Ensure patient comfort and privacy.
- Warm gel, clean towels
- Select “Obstetric” preset for appropriate power levels and measurement packages
MOST COMMON ABNORMALITIES TO LOOK FOR WHEN IMAGING THE FOLLOWING STRUCTURES:
Profile, nasal bone, nose/lips, mandible, palate, orbits.
Cleft lip and palate
Cystic hygroma
Exophthalamus
Proptosis
Prominent eyes
Hypertelorism
Hypotelorism
Microphthalmia
Anophthalmia
Facial asymmetry
Macroglossia
Micrognathia
Nasal bone absent or hypoplastic
Head
BPD, HC, Corpus callosum, CBM, NSF, CM, Ventricles
Choroids plexus cysts(CPC)
Agenesis of the corpus callosum
Dandy-Walker cyst
Echogenic brain focus or foci
Encephalocele
Holoprosencephaly
Intracranial cyst
Clover leaf skull
Macrocephaly
Microcephaly
Ventriculomegally
Arnold chiari malformation
Dandy-Walker malformation
Arachnoid cysts
Intracranial bleed
Posterior fossa cyst
Vein of Galen aneurysm
Anencephaly
Aqueductal stenosis
Intracranial teratomas
Heart
4chambers, LVOT, RVOT, Arrowhead view, heart beat, aortic and ductal arch
Bradycardia
Tachycardia
Heart axis towards the right
Enlarged heart
Ventricular septal defect (VSD)
Atrial septal defect (ASD)
Coarctation of the aorta
Double outlet right ventricle
Hypoplastic left heart syndrome
Hypoplastic right heart syndrome
Single ventricle
Tetralogy of Fallot
Cardiac rhabdomyoma
Ebstein’s anomaly
Endocardial cushion defect (atrioventricular canal)
Ectopia cordis (pentralogy of Cantrell)
Common arterial truncus
Premature atrial contractions
Transposition of the great arteries
Bright echoes in the heart
Left/right heart enlargement
Right atrial enlargement
Pericardial effusion
Small chest
Pleural effusion
Chest cavity
Pericardial effusion
Small chest
Enlarged heart
Pleural effusion
Cystic masses
Cystadenomatoid malformations
Diaphragmatic hernia
Chest wall haematoma
Pericardial cyst
Tracheal atresia
Mediastinal teratoma haemothorax
Diaphragm,liver,GB,bowel
Diaphragmatic hernia
Anal atresia
Duodenal atresia
Gastrointestinal atresia or stenosis
Gastroschisis
Omphalocele
Meconium cyst
Meconium ileus
Umbilical hernia
Tracheooesophageal atresia or fistula/oesophageal atresia
Ascites
Midgut volvulus
Small bowel atresia
Meconium peritonitis
Dilated stomach
Dilated duodenum
Dilated bowel
Echogenic mass
Adrenal haemorrhage
Hepatic tumour
Neuroblastoma
Ovarian cyst with haemorrhage
Echogenic bowel
Cystic fibrosis
Intragut or intrabdominal bleed
Calcification
Gallstones
Teratoma
Kidneys and Adrenals
Hydronephrosis
Ectopic ureter
Infantile polycystic kidney disease
Multicystic dysplastic kidney
Posterior urethral valves
Reflux (<6mm PUJ)
Ureterocele
Ectopic ureter
Pelvo-uretero junction obstruction
Ureterovesicle junction obstruction
Horseshoe kidney
Pelvic kidney
Renal agenesis
Ureterocele
Adrenal haematoma
Adrenal mass
Cord and insertion
Omphalocele
Gastroschisis
Umbilical hernia
One umbilical artery
Bladder and Gender
Absent bladder
Renal agenesis
Bladder exostrophy
Dilated bladder
Spine sagittal, coronal,axial
Spina bifida
Myelomeningocele
Myeloschisis
Meningocele
Cystic masses
Solid masses- Sacrococcygeal teratoma
Lower limbs
Rocker-bottom feet
Polydactyly
Achondroplasia
Achondrogenesis
Absent digits
Absent limbs
Bowing
Clinodactyly
Club foot
Fractures
Joint contractures
Mesomelic shortness
Muscle wasting
Rhizomelic shortening
Limb shortening
Upper limb
Polydactyly
Achondroplasia
Achondrogenesis
Absent digits
Absent limbs
Abnormal thumb
Bowing
Clenched hands
Clinodactyly
Fractures
Joint contractures
Mesomelic shortness
Muscle wasting
Radial hypoplasia
Rhizomelic shortening
Short limbs
Limb shortening
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SCANNING TECHNIQUE
IMAGES TO CHECK GROWTH
Biparietal Diameter and Head Circumference (BPD AND HC):
The fetal head measurement must be taken in a cross sectional approach to include the skull, thalamus, cavum septi pellucidi and it must be symmetrical. The fetal head should be imaged laterally through the parietal bone. The measurement is from the outer edge to the inner edge of the cranium .
**Note: The cerebellum must NEVER be seen in this image or the probe is too caudal which can give an inaccurate size of the foetal head.
Abdominal Circumference (AC):
The abdominal circumference is taken with a transverse image to include the stomach, portal vein and the spine in a true tranverse plane. The ribs may or may not be seen but must be symmetrical if included. It should be a circle at 18-20 weeks and no compression by external forces. It is best taken with the baby supine or lateral because if the baby is prone then the rib shadows make it difficult to check the correct level. The measurement must be taken around the waist on the edge of the skin layer.
**Note: The kidneys should not be seen in the AC image or the plane is too caudal.
Femur Length (FL):
The femur bone must only be imaged when it is parallel to the probe as it will not be foreshortened. The lateral edge of the shaft is measured from the greater trochanter to the lateral femoral condyle.
**Note: Do not take the measurement if the femur is oblique. It can be underestimated if the medial edge is measured on the deeper femur.
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IMAGING
- Do not have your colour scale set too low or ‘bleeding’ over walls will occur and a small VSD could be missed or a coarctation.
- Make sure the baby is over 18weeks
- Dynamic range is narrowed for the heart.
Basic Hardcopy Imaging
A morphology series should include the following minimum images:
- Cervix length (most accurate assessment is done transvaginally)
- Placenta and placental cord insertion
- Placenta to cervix distance transvaginally ideally
- BPD
- HC
- AC
- FL
- REPORT
- Ventricles and choroids (Lateral ventricle measurement posterior horn)
- Cerebellum, NF, Cisterna Magna all measured.
- Corpus Callosum sagittal view
- Profile
- Nose and lips
- Eyes/lenses and orbits
- Palate
- Mandible
- Spine (sagittal, coronal and transverse)
- Pelvis
- Arms, hands, fingers
- Legs, feet, toes
- Diaphragm (left and right)
- Stomach shown on left side
- Kidneys (long and transverse) with renal pelvis measurement done in transverse
- Bladder
- Cord insertion
- 2 umbilical arteries
- Heart- 4 chamber, IVS/IAS, LVOT, RVOT, PAV, Arrowhead view, Aortic arch and ductal arch (in B mode and colour)
- Heart rate