Fetal Biometry in Second & Third Trimester

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Questions and Answers

What is the normal measurement for the atrium?

10.5 mm

8.0 mm

4.5 mm

6.5 mm (correct)

What action should be taken if the atrium measures greater than 10 mm?

Immediate surgical intervention required

Repeat measurement in one week

Serial imaging and further evaluation are warranted (correct)

No further action needed

In evaluating nuchal skin fold thickness, what is considered a normal value up to 20 weeks’ gestational age?

7 mm or less

6 mm or less

5 mm or less (correct)

4 mm or less

What should be evaluated when assessing the thorax?

Fetal breathing Signup and view all the answers

Where should the thickness of the nuchal skin fold be measured?

In the plane containing the cavum septi pellucidi, cerebellum, and cisterna magna Signup and view all the answers

What is the primary use of measuring abdominal circumference in fetal assessments?

To monitor normal fetal growth and disturbances Signup and view all the answers

Which anatomical landmarks should be visible when correctly measuring abdominal circumference?

Lower ribs and fetal stomach Signup and view all the answers

During the measurement of femur length, which part is excluded?

Epiphysis Signup and view all the answers

Why is femur length considered less reliable for establishing gestational age?

There are significant biological variabilities Signup and view all the answers

Which of the following parameters is notably correlated with Down’s Syndrome?

Short humerus length Signup and view all the answers

What is the relationship between the lengths of the tibia and fibula in fetal measurements?

Fibula is lateral to tibia and shorter Signup and view all the answers

In ocular measurements, what is the binocular distance measured from?

Lateral orbital rim Signup and view all the answers

Which statement accurately describes the accuracy of sonography in predicting fetal weight?

It is inaccurate but can estimate weight trends. Signup and view all the answers

What angle is required for an exact BPD measurement?

90 degrees Signup and view all the answers

What is the normal range for the Cephalic Index (CI)?

0.7 - 0.86 Signup and view all the answers

When the fetal head is dolichocephalic or brachycephalic, which measurement is considered more accurate than BPD?

Head circumference (HC) Signup and view all the answers

In the context of the Cephalic Index, when is the BPD considered unreliable?

When CI is less than 0.7 Signup and view all the answers

Which structure should not be included in the fetal head circumference (HC) measurement?

Scalp Signup and view all the answers

At which location should the measurement of the lateral ventricles be taken?

At the level of the occipital horns and atria Signup and view all the answers

What is the normal size range for the Cisterna Magna?

2-11 mm Signup and view all the answers

What does the abdominal circumference (AC) measurement reflect?

Aberrations of growth including both restrictions and macrosomia Signup and view all the answers

How is the orientation of the heart in a fetus different from that in an adult?

The heart lies more transversely in a fetus. Signup and view all the answers

Which part of the heart is closest to the anterior chest wall in a fetus?

Right ventricle Signup and view all the answers

What is necessary to visualize the four chambers of the heart in a fetal ultrasound?

A view with the beam perpendicular to the septum. Signup and view all the answers

Which structure should be located to obtain a four-chamber view of the fetal heart?

Fetal stomach Signup and view all the answers

In a fetus, where is the apex of the heart directed?

Toward the left anterior chest Signup and view all the answers

What is a key factor to observe when assessing fetal limb bones for anomalies?

Presence of bowing, fractures, and demineralization Signup and view all the answers

Which condition is associated with an increased risk for aneuploidy as indicated by short femur and short humerus measurements?

Trisomy 18 Signup and view all the answers

Why is it clinically important to provide information regarding gender identification in fetal assessments?

To identify gender-linked disorders risk Signup and view all the answers

What does positive hand movement in a fetus indicate during an ultrasound?

Normal fetal tone Signup and view all the answers

How can individual fingers be assessed during a fetal ultrasound?

Viewing fingers in the sagittal plane Signup and view all the answers

What is the most widely measured long bone during a fetal examination?

Femur Signup and view all the answers

What may indicate a chromosomal disorder, such as trisomy 18, during a fetal ultrasound?

Clenching of hands Signup and view all the answers

Which factor might lead to bladder under-fulfillment in normal situations?

Decreased ingestion of fluid Signup and view all the answers

During fetal assessments, which of the following is important to verify as per the guidelines for obstetric examinations?

Presence or absence of legs and arms Signup and view all the answers

What anatomical structures are noted by moving the transducer inferior to the iliac crests?

Femoral echo Signup and view all the answers

Which feature indicates that the apex of the heart is correctly positioned in a fetal echocardiogram?

It points towards the fetal left side Signup and view all the answers

What is the significance of an echogenic intracardiac focus (EIF) in fetal echocardiography?

It is a normal variant in many pregnancies Signup and view all the answers

Which of the following is least likely to be assessed in the standard fetal echocardiography?

Left ventricular outflow tract (LVOT) Signup and view all the answers

What percentage does the four-chamber view alone have for detecting cardiac anomalies?

33-63% Signup and view all the answers

In a normal fetal heart assessment, which characteristic is expected regarding the size of the chambers?

Right and left chambers are approximately equal in size Signup and view all the answers

What is a critical visual feature that should be observed in the four-chamber view of the heart?

Symmetric ventricular septum Signup and view all the answers

Which statement regarding the movement of the mitral (MV) and tricuspid valves (TV) in real-time imaging is correct?

They move synchronously with the heart rate Signup and view all the answers

Why is only a portion of the atrial septum usually visible in fetal echocardiography?

It is not fully developed until birth Signup and view all the answers

Study Notes

Second & Third Trimester Fetal Biometry and Growth

Fetal cardiac activity needs checking at the beginning of each ultrasound study to confirm the fetus is alive.
If fetal demise or obvious anomaly is initially recognized, the sonographer should involve the physician immediately.

Second and Third Trimester Protocol

Check for fetal cardiac motion and heart rate.
Cervical length should be greater than 3 cm.
Measure biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), femur length (FL), humerus length (HL), cerebellum/head circumference (CM), lateral ventricles, and amniotic fluid index (AFI).
Understand and document presentation and lie.
Utilize ADD (Additional Data Display) as appropriate.

Basic Protocol

Document cardiac activity.
Determine the number of fetuses.
Estimate fetal age.
Document measurements (BPD, HC, AC, FL, HL).
Note fetal position.

Basic Protocol (Additional Information)

Record placental cord insertion.
Count the number of vessels in the cord.
Examine the kidneys.
Note umbilical cord insertion.
Assess the bladder, stomach, and four-chamber heart/outflow tracts.
Document placental position.

2nd & 3rd Trimester Ultrasound

Measure cerebral ventricle width, cerebellum size, cisterna magna size, spine, diaphragm and heart situs.
Measure 12 long bones, hands, and feet.

Cervical Length

Measure cervical length from the internal to the external os.
Avoid transabdominal measurements if the cervix cannot be clearly visualized, use transvaginal or translabial approaches instead.
Cervical length should be 3 cm or longer.

Fetal Presentation

Describe fetal lie in relation to the maternal long axis.
If fetal lie is oblique, describe the quadrant of the uterus containing the fetal head and direction/position of the spine.

Fetal Presentation Types

Vertex/Cephalic: Head down; relationship of fetal occiput to the maternal pelvis.
Breech: Buttocks first; Frank breech may require C-section; complete breech may be turned; relationship of fetal sacrum to the maternal pelvis.
Transverse: Lying sideways, look for placenta previa or a mass in late pregnancy, and prevent movement into vertex/cephalic presentation.

Type of Breech

Complete breech: Fetal hips and knees flexed with feet pressed against chest.
Incomplete breech: Buttocks present but one or more legs are extended.
Frank breech: Buttocks are presented, but the legs are extended, with knees and feet near the head.

Situs

Situs Solitus: Normal organ arrangement (right side gallbladder, apex of heart pointing to left, fetal aorta left of midline).
Fetal aorta slightly to left of midline, anterior to spine; inferior vena cava is to right of midline and slightly more anterior to aorta.
Document the right and left sides of the fetus to ensure normal situs.

Fetal Anatomy - Cranium

Ossifies by 12 weeks.
Check skull contour at highest levels; oval shape.
Pathology or fetal death may distort skull shape.
Brain structures more hypoechoic due to water content.
Sulcus and gyrus are more echogenic.
Becomes more complex as pregnancy progresses.

Cranial Anatomy

Examine the cerebellum, choroid plexus, cisterna magna, lateral ventricles, midline falx, and cavum septum pellucidum (CSP).

The Cranium

Midline falx is an important landmark because its presence indicates separation of the cerebrum.

The Cranium - Major Scan Planes

Three major planes (axial (transverse) is used for most scans except the cerebellar view, which is axial/oblique) accommodate three views:
Thalamic view (taken at the level of BPD and HC measurements).
Ventricular view (obtained through the atrium of the lateral ventricle).
Cerebellar view (angled through the posterior fossa, cisterna magna).

Ventricular View

Fetal ventricular system consists of two paired lateral ventricles, a midline third ventricle, and a fourth ventricle adjacent to the cerebellum.
Contains cerebrospinal fluid (CSF).
Choroid plexus tissue produces CSF within the lateral ventricles.
Located within the roof of each ventricle, except at the frontal ventricular horns.

The Cranium: Lateral Ventricles

Measure the posterior horn of a lateral ventricle (atrium) directly across the posterior portion, perpendicular to the long axis of the ventricle not the falx.
Calipers positioned at the junction of the ventricular wall and lumen/cavity.
Normal atrium measures 6.5 mm.
Measurements of >10 mm warrant serial imaging and further evaluation.

The Cranium: Choroid Plexus

This should be assessed but not measured.

Transthalamic Plane

Identifying cavum septum pellucidum, thalami, cerebral peduncles, and third ventricle.

Thalamic View

Identify thalami and third ventricle.
Identify the calvaria.

The Transcerebellar Plane

Locate the cerebellum, cerebellar vermis, and cisterna magna.
Include measurement of cavum septi pellucidi.

Nuchal Skin Fold

Measure nuchal skin fold thickness in the plane containing cavum septi pellucidum, cerebellum, and cisterna magna.
5 mm or less up to 20 weeks' gestational age is normal.

The Thorax

Evaluate fetal breathing, size, texture, and location of masses.
Note bordering structures such as the heart (medially) and rib cage (laterally).
Observe the diaphragm (inferiorly).

The Thorax (Homogeneous Lungs)

Lungs are lateral to the heart, superior to the diaphragm.
Include stomach, lungs, and placenta in the view.

The Heart

The heart is more transverse in the fetus compared to an adult.
The apex of the heart points to the left anterior chest.
Observe the right and left ventricles in a four-chamber view.
Observe the four chamber of the heart taken with a beam perpendicular to the heart or in a view with a perpendicular beam.

The Heart (Four-Chamber View)

Locate the fetal stomach and angle the transducer towards the head to visualize the four chambers (locate the fetal heart with the beam perpendicular to the heart, or a perpendicular view).
Document position, situs, axis, and if there are equal-sized right and left ventricles/atria.
Check for an interventricular septum and normal placement of tricuspid and mitral valves.
Document normal rhythm and rate.

The Heart - Echogenic Foci

A bright echogenic structure within the heart chamber, which persists despite transducer position changes, is considered an echogenic intracardiac focus (EIF).
Normal variation within many normal pregnancies.
May be associated with increased risk of aneuploidy and cardiac defects.

Fetal Cardiology

AIUM/ACR standards include four-chamber views, fetal heart position, and LVOT and RVOT if applicable.
With outflow tracts, 83-85% sensitive for detecting anomalies.

Four-Chamber View

Label each chamber (RV, LV, RA, LA).
Measure each chamber.
Check for symmetry in the ventricular septum.
Observe the atrial septum.

Left Ventricular Outflow Tract

Identify the left ventricle (LV), right ventricle (RV), interventricular septum (IV septum), aorta.
Document the aorta's normal caliber,+/- LA, +/- RA.
Note medial wall ascending aorta, merges with top IV septum.
Document possible pathology (VSD, tetralogy of Fallot, transposition, truncus arteriosus).

Right Ventricular Outflow Tract

Identify the branching of the main PA into the right PA and ductus arteriosus.
Ascending aorta should be seen in cross section with the descending aorta to the left of the spine.
Confirm the PA crosses the anterior to the ascending aorta.
Note possible pathology (transposition, truncus arteriosus).

Thoracic Vessels

Assess the fetal aortic arch, pulmonary artery, trachea, and esophagus.

Ductal Arch/ductus arteriosus

Confirm correct orientation and communication between the aorta and pulmonary trunk.
Look for a hockey-stick appearance.
Note the placement of the ductus arteriosus (anteriorly).

The Diaphragm

Note the diaphragm's appearance, which differs from that of an adult.

The Hepatobiliary System and Upper Abdomen

The liver is the largest organ in the upper abdomen; the left lobe is usually larger than the right lobe.
The liver appears as pebble-gray and is discernible by its corresponding portal and hepatic vessels.

The Hepatobiliary System and Upper Abdomen (Liver Image)

Observe the liver, diaphragm, and bowel.

The Gastrointestinal System

Fetal bowel is typically larger than the fetal liver, and can be hyperechoic (similar in echogenicity to bone).
Assess the presence of an echogenic bowel (small bowel as fluid-filled rings).
Fetal bowel with hyperechogenicity is associated with risk of aneuploidy and neonatal/childhood pathology.

The Hepatobiliary System and Upper Abdomen (abnormal fluid around liver)

Check for fluid collections around liver margins.
Ascitic fluid, fluid retention, anemia, or congenital anomalies can indicate fluid collection.
Assess for liver masses; they are not common but may be present.

The Hepatobiliary System and Upper Abdomen (Gallbladder)

Examine the fetal gallbladder, which appears as a cone- or teardrop-shaped cystic structure located below the left portal vein in the right upper abdomen, to distinguish it from the left portal vein.

Gallstones and Sludge

Evaluate for gallstones and sludge.

The Gastrointestinal System (Stomach)

The fetal stomach is present early, filling as a result of swallowing amniotic fluid;
full stomach should be seen in all fetuses beyond 16 weeks.

The Urinary System

Evaluate the kidneys and bladder.
Adrenal glands are usually more prominent in the fetus than in adults and positioned adjacent to the kidneys.
Kidneys appear as ovoid retroperitoneal structures with indistinct borders during the second trimester.
Renal pelvis measurement is in sagittal view when fluid is present; it is considered abnormal above certain measurements related to gestational age.

The Urinary System (Adrenals)

Assess the adrenals, usually seen by the 20th week and taking a transverse view above the kidneys; they should appear as rounded, bean-shaped structures.

Kidneys vs Adrenals (Image)

Differentiate between kidneys and adrenals in a transverse plane.

The Urinary System (Bladder)

The bladder may not always be completely full due to decreased fluid ingestion.
The bladder refills normally.

The Genitalia

Assess for gender identification to identify possible risk for gender-linked disorders, such as aqueductal stenosis or hemophilia, or for determining chorionicity in multiple pregnancies.

The Upper and Lower Extremities

Check for the presence of legs and arms;
Short femur and short humerus signify increased risk for aneuploidy.
Assess for unusual anatomic configurations of fetal limb bones such as bowing, fractures, or demineralization (common in skeletal dysplasia).
Evaluate hand and finger movement within a sagittal plane or evaluate hand clench throughout examination.
Individual fingers can often be counted in the first trimester of pregnancy.

The Upper and Lower Extremities (Hand Observation)

Note if hands are clenched in examination or if finger movements are normal.

The Upper and Lower Extremities (Measurement of Bones)

Evaluate bone length as an important part of assessing fetal growth.
Femur is measured from the neck of the femur to its distal end, not including the epiphyses, to assess the ossified portion.
Measure all long bones if a significant difference is noted in timing compared to other parameter measurements.

The Upper and Lower Extremities (Humerus)

Assess the humerus for any abnormalities in ossification or length in comparison to femur length.

The Upper and Lower Extremities (Tibia and Fibula)

Measure tibia and fibula length.
Tibia will be longer and fibula will be thinner and lateral to tibia.

The Upper and Lower Extremities (Radius and Ulna)

Measure radius and ulna.
Ulna will be longer than radius on proximal and will be the same on distal views.

Ocular Measurements

Measure interocular distance (ICD), binocular distance, and ocular diameter.
Measure these parameters if fetal position prohibits more complete fetal assessment.

Fetal Weight

Sonography is not completely precise for assessing fetal weight, and accuracy decreases with increasing gestational age and particularly if assessing post-term fetuses.
Serial sonograms are helpful for monitoring weight changes and documenting fetal growth.

Extra Fetal Obstetric Evaluation

Evaluate the placenta, amniotic fluid, and pelvis.

Umbilical Cord

Examine the umbilical cord, noting the presence of two arteries and one vein.
Cord twists may be considered associated with poor pregnancy outcomes.
The umbilical cord is easily imaged on both sagittal and transverse sections.
Umbilical vein diameter increases throughout gestation and reaches a maximal diameter of 0.9 cm by 30 weeks.
Assess for placental insertion and location; velamentous insertion is atypical.

Umbilical Cord (Insertion, etc.)

Document placental insertion, important for procedures like amniocentesis.
Report atypical insertion as velamentous insertion.

Placenta (Image)

View the placenta for assessment of size, position, and other features.

Amniotic Fluid

Amniotic fluid permits fetal movement, maintains intrauterine pressure, protects the fetus from injury, and results from production by the cord and membranes as well as the lungs, skin, and kidneys.
Oligohydramnios is low amniotic fluid; polyhydramnios is high amniotic fluid.

Amniotic Fluid (Images)

Locate and assess the amniotic fluid.

Membranes

Assess the amnion and inner/outer membranes, typically not visualized during the second and third trimesters.
The amnion is contiguous with the membrane lining the umbilical cord; at the umbilical cord's insertion point, the amnion expands over the surface of the chorionic part of the placenta.

Estimation of Fetal Age & Measurements

Use Naegele's rule (LMP + 3 months + 7 days) for due date estimations.
Utilize CRL, BPD, HC, AC, FL, and HL for more accurate estimations.

Estimation of Fetal Age: Second Trimester Measurements

Measure BPD, HC, AC, FL, and HL.

Additional Measurements

Measure cerebellum size/occipitofrontal diameter (OFD); lateral ventricles/cephalic index (CI).

Biparietal Diameter (BPD)

Assess the BPD, including the falx, thalamus, third ventricle, cavum septum pellucidum.
Calipers are placed outer-to-inner, and the angle should be 90 degrees between 10- and 12-weeks gestation, decreasing in reliability after the 26th week.

BPD and HC

Assess the BPD/calvaria, third ventricle, thalami, and CSP.
Ensure that the calvaria is smooth and symmetrical;
Assess the presence of CSP within the brain's anterior portion.
Position calipers circumferentially around the calvarial wall without including the calvarial wall.

Occipitofrontal Diameter (OFD)

Measure OFD.
Use image containing BPD for better accuracy.
Ensure 90-degree perpendicularity to the fetal BPD.

Cephalic Index

Calculate cephalic index (CI) using the formula C.I. = BPD / OFD x 100.
A CI of 0.7 to 0.86 is normal; below 0.7 is dolichocephalic; above 0.86 is brachycephalic.

Head Circumference (HC)

Measure HC on the same image as BPD.
Don't include the scalp/calvaria.
HC is more accurate than BPD for dolichocephalic or brachycephalic heads.
Don’t consider cerebellum in measurement area.

Additional Measurement Techniques

Document the lateral ventricles in an axial view.
Measure across the ventricle, near the posterior tip of the choroid plexus, perpendicular to the axis of the lateral ventricle in the axial view.

Cerebellum, Cisterna Magna

Assess the cerebellum and cisterna magna in an axial view of the posterior fossa.
Useful for gestational age determination when other measurements aren't possible.

Cerebellum/Cisterna Magna Measurements

Assess cerebellum size and shape, along with vermis connection.
Measure cerebellar width.
Measure cisterna magna depth: normal 2-11 mm, average 5-6 mm.

Cerebellum/Cisterna Magna Measurements (Transverse Plane)

Assess the cerebellum in a transverse plane, measuring across the cerebellar hemispheres at the level of the cerebellar hemispheres.
Measure from the vermis to the inner skull.

Abdominal Circumference (AC)

Assess the liver, which is the largest abdominal organ.
AC reflects growth aberrations, such as growth restriction and macrosomia.
Measure AC at the point of the liver's greatest transverse diameter.

Abdominal Circumference (Measurement Plane)

Measure AC in a plane positioned with the umbilical portion of the left portal vein positioned midline within the liver, with the curve towards the right.
Measure across skin line to encompass soft tissues and subcutaneous fat, and note fetal spine, umbilical vein, portal sinus, and adrenal glands.

Abdominal Circumference (Observation Checklist)

Verify position with fetal spine, fetal stomach, umbilical vein and portal sinus, and adrenal glands for appropriate placement and symmetry.

Femur Length (FL)

Measure length from the neck of the femur to the distal end of the femoral condyle, excluding epiphyseal parts.
FL remains less affected than other measures by IUGR.
Combination of FL, BPD, and AC are used to determine fetal weight; FL is less reliable in establishing gestational age.

Femur Measurement

Place calipers on the ossified part of the femoral diaphysis, measuring from end to end.

Humerus Length (HL)

Measure HL less affected by parental height than FL and is a stronger marker of Down Syndrome than short femur.
Measure is from the ossified part of the diaphysis.
Identify fetal spine, humerus, and scapula for proper placement.

Humerus Measurement (Procedure)

Obtain an image of the fetal spine in the upper thoracic/lower cervical region and identify the scapula.
Rotate transducer until the long axis of the humerus is clearly visible. Measure the humeral shaft only (diaphysis); do not include any proximal humeral points.

Tibia and Fibula Measurements

Notice that the tibia is longer than the fibula and the fibula is thinner, lateral to the tibia.
Measure the length of tibia and fibula from point to point on image.

Radius and Ulna Measurements

Locate the ulna and radius.
Ulna is longer than radius on the proximal view and both are of equal length on the distal view.

Ocular Measurements (Procedure)

Locate the lateral orbital rim.
Perform measurements if necessary.

Fetal Weight (Important Points)

Document weight changes from serial sonograms to assess changes.

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Description

This quiz covers essential protocols for assessing fetal biometry during the second and third trimesters of pregnancy. Key aspects include measuring fetal parameters, checking cardiac activity, and understanding fetal position and growth. Perfect for sonographers and medical students focusing on obstetrics.