OB ARDMS

Fetal Position and Developmental Anomalies

  • Understanding fetal positioning is crucial for assessing development:
    • Transverse Position
    • Parenthesis around maternal right (rt)/left (lt).
    • Breech Presentation
    • Cephalic Presentation
    • Agenesis of Corpus Callosum:
    • Definition: Absent cavum septum pellucidum.
    • Chiari Malformation:
    • Identified by the "banana sign" on ultrasound.

Common Anomalies and Their Associations

  • Open Neural Tube Defects (NTD):
    • Increased measurement of Maternal Serum Alpha-Fetoprotein (MSAFP).
  • Holoprosencephaly:
    • Characterized by incomplete cleavage and rotation of the early forebrain.
  • Vein of Galen Aneurysm:
    • Requires evaluation with color Doppler imaging.
  • Brachycephaly:
    • Associated with Trisomy 21 (T21).
  • Right Ventricular Outflow Tract (RVOT):
    • Involves the Main Pulmonary Artery.

Blood Flow Dynamics

  • Foramen Ovale:
    • Blood flows from the right atrium to the left atrium (left side).
  • Umbilical Vein to Ductus Venosus:
    • Connects to the Inferior Vena Cava (IVC).
  • Ductus Venosus:
    • Transforms into the Ligamentum Venosum post-birth.

Cardiac Positioning

  • Levoposition:
    • Defined as normal heart positioning.
  • Heart Position Classifications:
    • Levocardia:
    • Definition: Situs inversus; heart located on the left side with normal axis, yet with all thoracic and abdominal organs reversed.
    • Dextroposition:
    • Heart located on the right side with apex pointing left.
    • Dextrocardia:
    • Heart positioned on the left, with apex pointed right.

Thymus and Congenital Heart Disease (CHD)

  • Thymus:
    • Located posterior to the sternum between major vessels (3VV), recognized as a hypoechoic structure bordered by the left and right mammary arteries.
  • CHD Relationships:
    • Associated with increased Nuchal Translucency (NT).
    • Atrioventricular Septal Defect (AVSD):
    • Also known as endocardial cushion defect or AV canal defect, commonly linked with Trisomy 21 (T21).

Neurological Anomalies

  • Iniencephaly:
    • Defined by posterior flexion of the neck.
  • Sirenomelia:
    • Characterized by fusion of lower extremities.
  • Polydactyly:
    • Refers to the presence of an extra digit.

Pulmonary Conditions

  • Pulmonary Hypoplasia:
    • Most commonly caused by diaphragmatic hernia.
  • Diaphragmatic Hernia:
    • Bowel is compared to liver, bone, and lungs.

Gastrointestinal Anomalies

  • Esophageal Atresia:
    • Associated with Trisomy 18 (T18).
  • Gastroschisis:
    • Linked with aspirin use; defect appears to the right of the umbilicus.
  • Omphalocele:
    • Associated with aneuploidy (T13, T18).

Sonographic Markers and Measurements

  • Echogenic Bowel:
    • Associated with Trisomy 21 and cystic fibrosis.
  • Amniotic Fluid Index (AFI):
    • Polyhydramnios (Poly) > 25; Oligohydramnios (Oligo) < 5, measured perpendicular to the posterior uterine wall.
  • MVP (Maximum Vertical Pocket):
    • Poly > 8; Oligo < 2.
  • Hydronephrosis:
    • Most commonly caused by ureteropelvic junction (UPJ) obstruction.
  • Prune Belly Syndrome:
    • Characterized by weakened abdominal wall musculature, typically caused by posterior urethral valves.

Renal Anomalies

  • Multicystic Dysplastic Kidney:
    • Differentiated from hydronephrosis based on random pattern of cyst formation.
  • Polycystic Kidney Disease (Autosomal Recessive):
    • Presence of multiple microscopic cysts.

Endocrine & Musculoskeletal Disorders

  • Hypophosphatasia:
    • Defined by low levels of alkaline phosphatase.
  • Club Foot:
    • Demonstrates the bottom of the foot in alignment with the tibia and fibula.
    • Associated with Trisomy 21.
  • Rocker Bottom Foot:
    • Associated with Trisomy 13 and Trisomy 18.

Additional Ultrasound Considerations

  • Vernix:
    • Typically identified in higher gestational weeks.
  • Di/Di Pregnancy:
    • Can manifest in both monozygotic and dizygotic twinning.

Hydrops Evaluation

  • Sonographic Features:
    • Requires identification of at least two features from the following:
    • Pleural effusion.
    • Pericardial effusion.
    • Ascites.
    • Scalp edema.
    • Anasarca.
    • Presence of hydrops associated with decreased MSAFP, as seen in Turner syndrome and Trisomy 21.

Conditions Associated with Turners and Genetic Syndromes

  • Turner Syndrome Features:
    • Characterized by cystic hygroma, hydrops, cardiac, and renal defects.
  • Meckel Gruber Syndrome:
    • Includes encephalocele, multicystic dysplastic kidneys or recessive polycystic kidneys, and polydactyly.

Amniocentesis and Chorionic Villi Sampling

  • Amniocentesis: Done at 15-16 weeks; indicated by elevated MSAFP, check for open NTD among other conditions.
  • Chorionic Villi Sampling: Conducted at 10-12 weeks; used for karyotyping, gestational age, viability; does not screen for NTDs.
  • Coelocentesis: Performed at 6 weeks; solely for karyotyping.

Placental Considerations

  • Succenturiate Placental Lobe: Ectopic piece of placenta not connected to the main placenta.
  • Placental Infarcts: Hyperechoic triangular-shaped areas from ischemia to placental villi.
  • Vasa Previa: Condition where placental vessels cover the cervical os.
  • Placenta Accreta: Invasion of less than 50% of the myometrium.
  • Placental Abruption: Presents with severe pain and bleeding due to early separation of the placenta, potentially resulting in fetal demise.

Cord Insertions and Types

  • Marginal Cord Insertion (Battledore): Attachment to the periphery of the placenta.
  • Velamentous Cord Insertion: Correlation with placental membranes, typically seen with vasa previa.

Umbilical Vein and Arteries

  • Persistent Right Umbilical Vein: Vein curves to the left, with the gallbladder being positioned medial to the vein.
  • Umbilical Arteries: Antegrade diastolic flow typically increases as pregnancy progresses.

Nuchal Translucency and Other Measurements

  • Nuchal Translucency: Measured between 11-14 weeks; taken in a midsagittal view from inner to inner borders.
  • Nasal Bone: Best visualized in the sagittal view.
  • Orbits: Measured in the axial view.
  • Femur Measurement: Measure from diaphysis to diaphysis.

Assessing Scoliosis and Ventricles

  • Scoliosis: Best evaluated in the coronal view.
  • Lateral Ventricle Measurement: Utilize landmarks such as the Cavum Septum Pellucidum (CSP) and Glomus of the Choroid Plexus.
  • Biparietal Diameter (BPD) and Head Circumference (HC): Measure using the thalamus and third ventricle as landmarks.
  • Cerebellar Measurement (CM): From the anterior-posterior posterior vermis to the inner cranium.

Gynecological Considerations

  • Ampulla: Most common site for ectopic pregnancies.
  • Molar Pregnancies:
    • Partial Molar Pregnancy: Presence of a fetus with heterogeneous molar tissue.
    • Complete Molar Pregnancy: Absence of a fetus, characterized by elevated hCG levels and theca lutein cysts.
  • Yolk Sac (YS): A diameter less than 5.6 mm is considered normal; measured from anterior to inner dimensions.

Hormonal and Reproductive Health

  • Transvaginal (TV) vs Transabdominal (TA) Measurement Characteristics:
    • TV: hCG of 1000-2000 correlates with gestational sac (GS) of 16 mm.
    • TA: hCG of 4000 correlates with GS of 25 mm.

Gravida and Parity Definitions

  • Gravida: Total number of pregnancies.
  • Parity: Number of births at or beyond 20 weeks.
    • Term: 37 weeks or more.
    • Pre-term: Between 20-36 weeks.
  • Low Levels of hCG: May indicate missed abortion, ectopic pregnancy, fetal demise, or incorrect last menstrual period (LMP).

Advanced Imaging Techniques

  • Power Doppler: Utilized to visualize low blood flow.
  • 3D Imaging: Effective for imaging intrauterine devices (IUDs).

Obstetrical Imaging**

  • Differentiating features of Gastroschisis vs. Omphalocele and other conditions.
  • Visual representation of Sacrococcygeal Teratoma and a fetus with Acrania.

Additional Anomalies and Measurements

  • Chiari Banana Sign: Technique to localize the Middle Cerebral Artery (MCA).
  • Brachycephaly: Recognized for its distinctive features in imaging.
  • Evaluating facial features:
    • Nose/Lips: Coronal image to rule out cleft lip.
    • Eyes: Assessed in an axial image.
    • AVSD & RVOT: Important congenital heart conditions to be recognized.

Amniotic Sac Measurements

  • Measurement of the cervix transvaginally is important; understanding normal anatomy and associated anomalies.