Study guide
16.3 First-Trimester Abnormalities
ARRT Sonography Primary
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1 Introduction & Exam Overview
1.1 Current Exam Facts & Logistics 1.2 Scoring, Section Minimums & the August 2026 Cut-Score Change 1.3 Official Blueprint & Study Strategy
2 Patient Care: Ethics, Legal Practice & Communication
2.1 Ethical & Legal Aspects of Patient Care 2.2 Interpersonal Communication & Patient Education 2.3 Physical Assistance, Monitoring & Sonographer Ergonomics
3 Patient Care: Safety, Emergencies & Infection Control
3.1 Medical Emergencies & Critical Findings 3.2 Infection Control & Hazardous Materials 3.3 Ultrasound Safety & Interventional Procedure Care
4 Image Production: Transducers & the Ultrasound Beam
4.1 Piezoelectric Effect & Transducer Construction 4.2 Beam Configuration: Near Field, Far Field & Focus 4.3 Transducer Types, Selection, Care & Malfunctions
5 Image Production: Pulse Characteristics & Resolution
5.1 Pulse Characteristics: PRF, PRP, SPL & Duty Factor 5.2 Resolution: Axial, Lateral, Temporal, Elevational & Contrast 5.3 Frequency, Bandwidth, Q Factor, Power, Pressure, Intensity & Amplitude
6 Image Production: Imaging Modes & Doppler Principles
6.1 B-Mode & M-Mode Imaging 6.2 Spectral Doppler: Pulsed Wave vs Continuous Wave 6.3 Color Doppler & Power Doppler
7 Image Production: Optimization Controls
7.1 Power, Gain, TGC, Depth & Focal Zone 7.2 Frame Rate, Line Density, Dynamic Range, Harmonics & Compounding 7.3 Doppler Optimization Controls
8 Image Production: Sound–Tissue Interactions
8.1 Speed of Sound & the Range Equation 8.2 Acoustic Impedance, Reflection, Refraction & Scattering 8.3 Attenuation, Absorption & Intensity
9 Image Production: Signal Processing, Display & Bioeffects
9.1 Receiver, Signal Processing & Analog-Digital Conversion 9.2 Postprocessing, Magnification, Panoramic & 3D/4D Imaging 9.3 Bioeffects & Output Display Measures
10 Image Production: Image Evaluation & Artifacts
10.1 Criteria for Diagnostic Quality & Annotation 10.2 Grayscale Artifacts 10.3 Doppler Artifacts
11 Image Production: Real-Time Interpretation & Informatics
11.1 Real-Time Imaging, Echogenicity & Echotexture 11.2 Color & Spectral Analysis: Measurements and Waveforms 11.3 Imaging Informatics: HIS, RIS, EMR, PACS & DICOM
12 Procedures: Abdominal & Transplant Vasculature
12.1 Aorta, Its Branches & the IVC 12.2 Portal Venous System & Hepatic Vasculature 12.3 Liver & Renal Transplant Sonography
13 Procedures: Liver
13.1 Liver Anatomy, Variants & Examination Technique 13.2 Diffuse Liver Disease 13.3 Focal Liver Lesions
14 Procedures: Biliary System, Pancreas & Spleen
14.1 Gallbladder & Bile Ducts 14.2 Pancreas 14.3 Spleen
15 Procedures: Urinary Tract, GI Tract & Other Abdominal Structures
15.1 Kidneys & Ureters 15.2 Bladder & Prostate 15.3 GI Tract, Adrenals, Lymph Nodes, Hernias & Peritoneal Cavity
16 Procedures: First-Trimester Obstetrics
16.1 Early Gestation: Normal Development & Structures 16.2 First-Trimester Measurements, Dating & Maternal Anatomy 16.3 First-Trimester Abnormalities
17 Procedures: Second/Third-Trimester Biometry & Fetal Survey
17.1 Standard Biometry: BPD, HC, AC, FL & Growth Assessment 17.2 Fetal Anatomic Survey: Head, CNS, Face & Spine 17.3 Fetal Anatomic Survey: Heart, Chest, GI, GU, Skeleton & Fetal Position
18 Procedures: Chromosomal, Genetic & Structural Abnormalities
18.1 Chromosomal & Genetic Abnormalities 18.2 Major Structural Anomalies by System 18.3 Fetal Infection, Neoplasms & Hydrops
19 Procedures: Placenta, Amniotic Fluid, Cord & Cervix
19.1 Placenta: Normal, Previa, Abruption & Accreta 19.2 Amniotic Fluid Assessment & Growth Disorders 19.3 Umbilical Cord & Cervical Assessment
20 Procedures: Fetal Assessment, Doppler & Multiple Gestation
20.1 Biophysical Profile & Fetal Surveillance 20.2 Fetal & Uteroplacental Doppler 20.3 Multiple Gestations, Assisted Reproduction & Maternal Disease
21 Procedures: Gynecology — Uterus
21.1 Uterine Anatomy, Myometrium & Fibroids 21.2 Endometrium: Cyclic Changes, Hyperplasia & Cancer 21.3 Cervix & Congenital Uterine Anomalies
22 Procedures: Gynecology — Adnexa & Pelvis
22.1 Ovaries: Normal, Functional Cysts & Benign Masses 22.2 Ovarian Malignancy, Torsion & Fallopian Tubes 22.3 Cul-de-Sac, Vagina & Pelvic Floor
23 Procedures: Neck & Scrotum
23.1 Thyroid & Parathyroid 23.2 Salivary Glands & Neck Lymph Nodes 23.3 Scrotum & Testes
24 Procedures: Breast & Peripheral Vascular
24.1 Breast & Axilla 24.2 Venous Extremity Doppler 24.3 Carotid Doppler & Post-Catheterization Complications
25 Procedures: Pediatric, Interventional & Miscellaneous
25.1 Neonatal Head, Spine & Hip Sonography 25.2 Pediatric GI & Noncardiac Chest 25.3 Ultrasound-Guided Interventions, MSK & Superficial Masses
16.3 First-Trimester Abnormalities
Key Takeaways Explain This Topic AI
Pregnancy failure is diagnosed when the mean sac diameter is 25 mm or greater with no embryo, or the crown-rump length is 7 mm or greater with no cardiac activity
Time-based failure criteria: no embryo with heartbeat 2 weeks or more after a scan showing a sac without a yolk sac, or 11 days or more after a scan showing a sac with a yolk sac
Ectopic pregnancy most commonly implants in the ampullary portion of the fallopian tube; sonographic clues include an adnexal mass or tubal ring, free fluid in Morison's pouch, and a uterine pseudosac
A complete molar pregnancy shows a vesicular snowstorm intrauterine mass, markedly elevated hCG, and frequently bilateral theca lutein cysts
Embryonic bradycardia below about 90 bpm carries a poor prognosis, and subchorionic hemorrhage appears as a crescent-shaped collection lifting the chorion off the uterine wall
Last updated: July 2026
Diagnosing Pregnancy Failure
To avoid ever mislabeling a normal early pregnancy as failed, strict consensus criteria (Doubilet/Benson, endorsed by the Society of Radiologists in Ultrasound) define diagnostic findings of pregnancy failure. A terminology note before the criteria: the 2024 SRU first-trimester lexicon retired several of the legacy words still used on older question banks — pregnancy failure is now early pregnancy loss , blighted ovum is anembryonic pregnancy , missed abortion is embryonic or fetal demise , pseudosac is intracavitary fluid , and heartbeat is cardiac activity . The measurement thresholds themselves are unchanged:
- Criterion Threshold
- Crown-rump length with no cardiac activity CRL >= 7 mm
- Mean sac diameter with no embryo MSD >= 25 mm
- Follow-up after a scan showing a sac without a yolk sac No embryo with heartbeat >= 2 weeks later
- Follow-up after a scan showing a sac with a yolk sac No embryo with heartbeat >= 11 days later
Findings that are suspicious but not diagnostic include CRL < 7 mm without cardiac activity, MSD 16-24 mm without an embryo, an empty amnion, an enlarged yolk sac (> 7 mm), and a small sac relative to the embryo — these call for a follow-up scan, not a final diagnosis.
Anembryonic Pregnancy and Embryonic Demise
An anembryonic pregnancy (historically called a blighted ovum ) is a gestational sac that develops without an embryo — the sac and often a yolk sac grow, but no embryonic pole forms. It meets failure criteria when the MSD reaches 25 mm with no embryo. Embryonic demise refers to an embryo that formed and then died: the hallmark is an embryo at or above the 7 mm CRL threshold without cardiac activity, confirmed with M-mode and high magnification before pronouncing absence of motion. Embryonic bradycardia is a warning sign: a heart rate below 90 bpm in the early embryo is associated with a high rate of subsequent demise, while rates of 90-110 bpm warrant short-interval follow-up.
Spontaneous Abortion Spectrum
Spontaneous abortion (miscarriage) is pregnancy loss before 20 weeks. The clinical types form a sequence the exam tests by definition:
Threatened abortion — vaginal bleeding with a closed cervix and a live intrauterine embryo; the pregnancy may continue.
Inevitable abortion — bleeding with a dilated/open cervix ; loss cannot be stopped. A sac low in the uterus or within the cervical canal supports this.
Incomplete abortion — only part of the products of conception have passed; the cervix is open and tissue remains in the uterus.
Complete abortion — all products expelled; the uterus is empty with a thin endometrium and the cervix closes.
Missed abortion — embryonic demise with retention of the nonviable pregnancy; no bleeding or passage of tissue, cervix closed.
Retained products of conception (RPOC) appear as an echogenic endometrial mass with demonstrable color Doppler flow; an endometrial thickness under about 8-10 mm with no focal mass makes significant RPOC unlikely. RPOC predisposes to hemorrhage and infection and may require evacuation.
Ectopic Pregnancy
An ectopic pregnancy implants outside the endometrial cavity and remains a leading cause of first-trimester maternal mortality from tubal rupture and hemorrhage. About 95% occur in the fallopian tube , and of tubal implantations the ampullary portion is the most common site (roughly 70%), followed by the isthmic portion. Less common sites include interstitial (cornual), cervical, cesarean scar, ovarian, and abdominal implantations. A heterotopic pregnancy — simultaneous intrauterine and ectopic gestations — is rare naturally (about 1 in 4,000-30,000) but rises toward 1 in 100 with assisted reproduction.
Risk factors: prior ectopic pregnancy (strongest), pelvic inflammatory disease (especially chlamydia) and tubal scarring, prior tubal surgery or sterilization, intrauterine device use, in-vitro fertilization, and smoking.
Sonographic signs with an empty uterus and positive hCG:
Adnexal mass or tubal ring (bagel/donut) sign — an echogenic ring separate from the ovary; the most specific finding is a live embryo with cardiac activity in the adnexa, though an extrauterine sac with yolk sac is also diagnostic.
Free fluid — echogenic free fluid in the posterior cul-de-sac (pouch of Douglas) or in the hepatorenal recess ( Morison's pouch ) suggests hemoperitoneum from rupture; scanning Morison's pouch is part of the ectopic workup.
Pseudosac — a central intrauterine fluid collection in 10-20% of ectopics, lacking the double decidual sign (see Section 16.1).
Gestational Trophoblastic Disease
Gestational trophoblastic disease (GTD) is abnormal proliferation of trophoblastic tissue. The complete hydatidiform mole is classically diploid 46,XX of entirely paternal (androgenetic) origin with no fetal tissue, markedly elevated hCG (often above 100,000 mIU/mL), hyperemesis, and a uterus large for dates. Sonography shows a heterogeneous intrauterine mass of countless small vesicles — the snowstorm or bunch-of-grapes appearance — with no embryo. Ovarian stimulation by the very high hCG produces bilateral multiloculated theca lutein cysts . A partial mole is triploid (typically 69,XXY) and may show a coexisting abnormal fetus with a focally cystic placenta. Complete moles carry a risk of persistent trophoblastic disease and choriocarcinoma , so hCG follow-up after evacuation is mandatory.
Subchorionic Hemorrhage
A subchorionic (subchorionic-placental) hemorrhage is bleeding between the chorionic membrane and the uterine wall, appearing as a crescent-shaped fluid collection lifting the chorion away from the myometrium. Its echogenicity varies with age — hyperechoic or isoechoic when acute, becoming hypoechoic/anechoic as it resolves — and it shows no internal blood flow on Doppler, distinguishing it from a vascular mass. Small collections in a pregnancy with cardiac activity usually resolve with good outcomes; large hemorrhages (involving a substantial portion of the sac circumference or elevating a large placental area) increase the risk of miscarriage, especially with advancing maternal age.