The anomaly scan, also known as a target or Level II anatomical scan, belongs to the specialty of maternal-fetal medicine and obstetrics. Its primary goal is the systematic clinical evaluation of major fetal organ systems, including the brain, heart, spine, kidneys, abdomen, and limbs. Using high-frequency sound waves transmitted transabdominally, clinicians construct two-dimensional and three-dimensional cross-sectional images of internal fetal structures. Standardized clinical practice guidelines from the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) and the American College of Obstetricians and Gynecologists (ACOG) define the precise anatomical planes required to confirm standard structural development or detect congenital malformations early in gestation.

The patient lies supine on an examination couch, with the lower abdomen exposed. Water-based acoustic gel is applied to the skin to eliminate air gaps. The sonographer places a transabdominal transducer against the abdomen, using cross-sectional imaging planes to measure fetal biometry (head circumference, biparietal diameter, abdominal circumference, femur length). Systematically, the operator examines fetal intracranial structures, facial profile, lip/palate, spine, four-chamber cardiac view, outflow tracts, stomach, kidneys, bladder, abdominal wall insertion, and four extremities. Placental location, umbilical cord vessels, and amniotic fluid index are documented. If visual resolution is limited by maternal body habitus or fetal position, transvaginal scanning or patient repositioning may be utilized. Images and measurements are archived, and a formal clinical report is compiled.

The evidence-based clinical advantages of a Level II anomaly scan include:

• Early Structural Detection: Identifies up to 70-80% of major structural malformations, enabling early medical intervention and specialized care planning (ISUOG Guidelines, 2023).
• Accurate Fetal Biometry: Measures critical growth parameters to establish a baseline for identifying intrauterine growth restriction (IUGR) or fetal macrosomia.
• Risk Refinement for Aneuploidy: Detects physical soft markers that refine individual risk assessments for Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13).
• Placental Localization: Diagnoses low-lying placenta or placenta previa early, reducing risks associated with unexpected third-trimester hemorrhage (ACOG Practice Bulletin No. 229).
• Amniotic Fluid Evaluation: Quantifies fluid volume to detect underlying fetal renal dysfunction, swallowing difficulties, or placental insufficiency.
• Optimized Delivery Management: Facilitates coordinated care pathways, allowing neonates with severe anomalies (e.g., congenital heart disease or diaphragmatic hernia) to be delivered in specialized tertiary hospitals.
• Non-Invasive Safety: Utilizes non-ionizing acoustic wave energy, presenting no proven biological hazards to the pregnant patient or developing fetus when operated under standard output indices (thermal and mechanical indices below 1.0).

Because an anomaly scan is a entirely non-invasive diagnostic ultrasound procedure, there is no physical recovery period. Patients can immediately resume normal daily activities, exercise, work, and dietary habits following the exam. If transvaginal imaging was required to assess cervical length or low placental location, minor localized pelvic pressure or mild discharge from ultrasound gel may occur briefly. If structural variations are identified during the scan, the recovery phase involves clinical counseling, emotional support, and consultation with maternal-fetal medicine specialists or clinical geneticists to outline management steps.

An anomaly scan is a diagnostic tool used to identify and evaluate various structural conditions, developmental variations, and pregnancy parameters, including:

• Central Nervous System Anomalies: Spina bifida, anencephaly, ventriculomegaly, agenesis of the corpus callosum, and Dandy-Walker malformations.
• Congenital Heart Defects (CHDs): Hypoplastic left heart syndrome, transposition of the great arteries, tetralogy of Fallot, ventricular septal defects, and atrioventricular canal defects.
• Gastrointestinal and Abdominal Wall Defects: Omphalocele, gastroschisis, congenital diaphragmatic hernia, duodenal atresia, and echogenic bowel.
• Renal and Genitourinary Abnormalities: Renal agenesis, hydronephrosis, polycystic kidney disease, and posterior urethral valves.
• Skeletal and Limb Dysplasias: Clubfoot (talipes), achondroplasia, limb reduction defects, and polydactyly.
• Placental and Fluid Conditions: Placenta previa, vasa previa, single umbilical artery, oligohydramnios, and polyhydramnios.
• Chromosomal Soft Markers: Increased nuchal fold, absent nasal bone, choroid plexus cysts, intracardiac echogenic foci, and pyelectasis.

Preparation for an anomaly scan is simple. Patients are usually advised to wear comfortable, two-piece clothing for easy access to the abdomen. Depending on gestational age and clinical unit guidelines, a moderately full urinary bladder may be requested to elevate the uterus out of the pelvis, though at 18 to 22 weeks, amniotic fluid generally provides sufficient acoustic windows. Patients should continue taking prescribed medications and eat normally; having a small snack or fruit juice 20-30 minutes prior to the scan can encourage fetal movement if the fetus is in a suboptimal position. Medical records, prior screening results (such as cell-free DNA or first-trimester screening), and baseline obstetric documentation should be brought to the appointment.

Diagnostic ultrasound has been used in clinical obstetrics for over five decades with no established structural, developmental, or carcinogenic risks to the fetus or mother when performed within safety guidelines. Diagnostic ultrasound uses non-ionizing mechanical sound waves, not radiation. Modern ultrasound equipment continuously displays the Thermal Index (TI) and Mechanical Index (MI), which clinicians monitor to keep acoustic output well within safe biological limits (TI < 1.0, MI < 1.0) according to the As Low As Reasonably Achievable (ALARA) principle. The primary non-physical risks involve potential psychological distress or anxiety if unexpected fetal structural anomalies or soft markers are identified, or false-positive results that necessitate further invasive testing such as amniocentesis.

The clinical journey for an anomaly scan begins with scheduling between 18+0 and 22+6 weeks of gestation. During the pre-procedure phase, the patient completes a medical history review and maintains a moderately full urinary bladder if instructed. The procedure phase occurs in an outpatient diagnostic suite, where a qualified sonographer or maternal-fetal specialist moves an ultrasound transducer over the maternal abdomen to systematically evaluate fetal organ systems; this takes 30 to 45 minutes. Recovery is immediate, requiring no downtime or restriction of normal activities. The post-procedure phase includes a direct medical debriefing of findings, a formal written report sent to the primary obstetric team, and referral for follow-up testing, fetal echocardiography, or genetic counseling if structural variations are identified.