OBGYN Ultrasound Midterm – Vocabulary Review

Vocabulary flashcards summarizing essential fetal anatomy, ultrasound measurement criteria, normal sonographic appearances, and common abdominal pathologies for the OBGYN midterm.

Biparietal Diameter (BPD)

Head measurement taken at the thalamic level; calipers placed outer skull table to inner skull table, perpendicular to the midline falx.

Abdominal Circumference (AC)

Measurement of the fetal abdomen at the level of the stomach and portal sinus/umbilical vein confluence; abdomen should appear round and kidneys should NOT be visible.

Femur Length (FL)

Long-bone measurement taken from the greater trochanter to the lateral femoral condyle; excludes cartilaginous epiphyses.

Crown-Rump Length (CRL)

First-trimester measurement from top of fetal head to bottom of torso; most accurate parameter for gestational dating up to 14 weeks.

Falx Cerebri

Bright echogenic midline structure separating the cerebral hemispheres on axial brain images.

Cavum Septum Pellucidum (CSP)

Box-shaped anechoic space between the frontal horns of the lateral ventricles; confirms correct BPD level.

Thalami

Paired ovoid structures flanking the third ventricle; seen symmetrically at the proper BPD plane.

Lateral Ventricles

Fluid-filled cavities within cerebral hemispheres; presence in BPD view indicates scanning too high.

Choroid Plexus

Echogenic tissue within the lateral ventricles responsible for CSF production.

Fetal Stomach

Round anechoic structure in the left upper abdomen filled with swallowed amniotic fluid.

Umbilical Vein

Anechoic vessel coursing toward the liver; joins the portal sinus in the AC plane.

Diaphragm

Curved hypoechoic line separating thoracic and abdominal cavities on sagittal/coronal fetal images.

Fetal Bladder

Central anechoic pelvic structure that fills and empties cyclically; flanked by umbilical arteries on color Doppler.

Fetal Kidneys

Paired bean-shaped organs posterior in the abdomen; should NOT be included when measuring AC.

Hyperechoic

Tissue that appears brighter than surrounding structures because it reflects more ultrasound (e.g., fetal bone).

Hypoechoic

Tissue that appears darker than surrounding structures because it reflects less ultrasound (e.g., diaphragm muscle).

Anechoic

Completely black on ultrasound due to absence of internal echoes (e.g., fluid in bladder, stomach, vessels).

Amniotic Fluid

Anechoic fluid surrounding the fetus; provides cushioning and allows visualization of anatomic detail.

Echogenic Bowel

Fetal bowel that appears as bright as bone; associated with infection, aneuploidy, cystic fibrosis or placental bleeding.

Double Bubble Sign

Paired anechoic bubbles representing stomach and proximal duodenum—classic for duodenal atresia.

Gastroschisis

Right-sided abdominal wall defect with free-floating bowel loops not covered by a membrane.

Omphalocele

Midline abdominal wall defect with herniated abdominal contents covered by a membrane and umbilical cord insertion into the mass.

Congenital Diaphragmatic Hernia

Herniation of abdominal organs into the thorax through a diaphragmatic defect, often causing mediastinal shift.

Outer-to-Inner (Caliper Placement)

Standard technique for BPD: place first caliper on the outer skull table nearest the probe and second on the inner skull table farthest from the probe.

Correct BPD Plane

Shows falx, CSP, and thalami; does NOT show lateral ventricles high in the head or cerebellum low in the head.

Incorrect BPD Plane

Image that includes cerebellum, lateral ventricles, or is obliquely angled—leads to inaccurate head measurements.

Correct AC Plane

Rounded abdomen with single umbilical vein at portal sinus, stomach bubble, and absence of kidneys and ribs.

Diaphysis of Femur

Long, ossified shaft of the femur measured for FL; exclude echogenic epiphyses at the ends.

Placenta

Fetal–maternal organ that appears homogeneous and moderately echogenic; evaluated for position, grade, and cord insertion.

Ribs (Fetal)

Curved hyperechoic structures forming the thoracic cage; help identify thoracic versus abdominal level.

Portal Sinus

Junction where the umbilical vein meets the left portal vein; landmark for the correct AC measurement level.

Spine (Fetal)

Series of paired echogenic lines representing the vertebral bodies and posterior elements; used to confirm orientation and detect defects.