US Obstetric Second/Third Trimester — Dictation, Appropriateness, and Dose for Residents

1. The Comprehensive Fetal Anatomy Scan — More Than Just a Checklist

It’s a busy outpatient OB day. You have three 18-22 week anatomy scans back-to-back, and each one is a 45-minute deep dive. Your attending expects every required view of the fetal heart, a perfect cisterna magna measurement, and a definitive statement on placental location relative to the os. Forgetting to document the three-vessel cord or the outflow tracts is not an option. This isn’t just about filling out a worksheet; it’s about systematically clearing every major organ system in one of the highest-stakes screening exams in medicine. When I was a resident, the sheer volume of required measurements felt overwhelming. The key is having a systematic approach and a solid template. We’ve built a ton of tools for trainees over at the residents and fellows resource hub, but let’s break down this specific scan right here.

2. What the Second/Third Trimester Anatomy Scan Covers and What Attendings Look For

The 18-22 week anatomy scan is the cornerstone of fetal structural evaluation. It’s designed to provide a comprehensive survey, from biometry for growth tracking to a detailed review of organ systems. Your attending is looking for a report that systematically addresses each of these key areas, confirming normalcy or clearly describing any abnormalities.

Here’s what your final report needs to answer:

• Fetal Biometry: Are the Biparietal Diameter (BPD), Head Circumference (HC), Abdominal Circumference (AC), and Femur Length (FL) appropriate for the gestational age? What is the Estimated Fetal Weight (EFW) and percentile?
• Structural Survey: Is every major organ system visualized and grossly normal? This includes the head, face, spine, heart, abdomen (stomach, kidneys, cord insertion), and extremities.
• Placental Evaluation: Where is the placenta located (anterior, posterior, fundal)? What is its distance from the internal cervical os? Are there any features concerning for an accreta spectrum disorder?
• Amniotic Fluid Volume: Is the amniotic fluid index (AFI) or single deepest pocket (SDP) within the normal range?
• Cervical Length: Is the cervix of normal length, or is there evidence of shortening that might increase preterm birth risk?
• Umbilical Cord: Is a three-vessel cord (two arteries, one vein) present? Is the cord insertion site normal?

3. Radiology Report Template for an Obstetric Second/Third Trimester Anatomy Scan

This template provides a reliable structure for your dictation. It ensures you hit all the required elements for a comprehensive and defensible report. You can adapt this for your institution’s macros in PowerScribe or other voice recognition software.

Technique

A real-time grayscale and color Doppler ultrasound of the gravid uterus was performed transabdominally. The patient’s bladder was empty to facilitate visualization of the lower uterine segment and cervix. A comprehensive fetal anatomic survey and biometry were performed.

Findings

Fetal Biometry and Gestational Age:
Number of fetuses: Single live intrauterine gestation.
Fetal cardiac activity: Present. Fetal heart rate is [___] bpm.
Fetal motion: Present.
Biparietal Diameter (BPD): [___] cm, corresponding to [___] weeks.
Head Circumference (HC): [___] cm, corresponding to [___] weeks.
Abdominal Circumference (AC): [___] cm, corresponding to [___] weeks.
Femur Length (FL): [___] cm, corresponding to [___] weeks.
Composite Gestational Age: [___] weeks [___] days, based on [LMP/prior US].
Estimated Fetal Weight (EFW): [___] grams ([__]th percentile), calculated via Hadlock formula.

Fetal Anatomic Survey:
Head: The calvarium, midline falx, cavum septi pellucidi, thalami, cerebellum, and cisterna magna are visualized and appear unremarkable. The lateral ventricles are normal in size, with the atria measuring less than 10 mm. The choroid plexus appears normal.
Face: The fetal profile, nasal bone, orbits, and lips appear intact and unremarkable.
Spine: Visualized in sagittal and transverse planes and appears grossly intact without evidence of spinal dysraphism.
Chest: The lungs are homogenously echogenic. A four-chamber view of the heart, left and right ventricular outflow tracts, and the three-vessel trachea view are visualized and appear grossly normal.
Abdomen: The stomach is visualized on the left. The kidneys and bladder are present and appear normal. The anterior abdominal wall is intact at the umbilical cord insertion site.
Extremities: Four extremities are visualized. Hands and feet are grossly identified.
Genitalia: [Male/Female/Not clearly visualized].

Placenta, Amniotic Fluid, and Cord:
Placenta: [Anterior/Posterior/Fundal] location, grade [___]. The placenta is clear of the internal cervical os, with the inferior edge measuring [___] cm from the os. No evidence of previa or accreta.
Amniotic Fluid: The amniotic fluid index (AFI) is [___] cm, which is within the normal range (5-25 cm).
Umbilical Cord: A three-vessel umbilical cord is visualized.

Maternal Structures:
Cervix: The transabdominal cervical length is [___] cm. The internal os is closed.
Uterus and Adnexa: The myometrium is unremarkable. The adnexa are grossly unremarkable.

Impression

1. Single live intrauterine gestation at [___] weeks [___] days, consistent with dates.
2. Estimated fetal weight is [___] grams, at the [__]th percentile for gestational age.
3. Grossly normal fetal anatomic survey for gestational age, with all required elements visualized and unremarkable.
4. Normal placental location, amniotic fluid volume, and three-vessel umbilical cord.
5. Cervical length is normal.

4. Free Template Sources from the Radiology Community

Building your own templates is a rite of passage, but you don’t have to start from scratch. Before you reinvent the wheel, know that two great free repositories exist, curated by and for radiologists. They are excellent starting points for nearly any study you’ll encounter on call.

• RadReport.org: Maintained by the RSNA, this is a comprehensive library of peer-reviewed templates covering nearly every modality and subspecialty. (https://radreport.org/)
• Radiology Templates (AU): An excellent, clean resource maintained by Australian radiologists with a strong focus on practical, clear templates for daily use. (https://www.radiologytemplates.com.au/home-page/)

5. The Next-Level Move: Free-Form Dictation with AI-Powered Structuring

The biggest friction with standard templates is the rigid, click-box nature of structured reporting. It can feel like you’re performing data entry instead of interpreting a study. You see a finding, but then you have to stop, find the right field, and document it before moving on. This breaks your flow.

The alternative is to dictate your positive findings in free form, just as you see them, and let an AI handle the tedious work of organizing them into a perfectly structured report. This is the core idea behind GigHz Precision AI. You can simply dictate, “The placenta is anterior and low-lying, with the inferior edge 1.5 cm from the internal os,” and the tool automatically populates the correct sections of the report, flags the finding, and can even suggest the appropriate follow-up recommendation based on society guidelines. It helps streamline the reporting process by combining the speed of narrative dictation with the clarity and compliance of a structured template.

6. When Should You Order an Obstetric Anatomy Scan? ACR Appropriateness Criteria

While the 18-22 week anatomy scan is a routine screening examination for all pregnancies, ultrasound is also the frontline tool for evaluating specific problems. The American College of Radiology (ACR) provides guidance on these scenarios.

For instance, in the case of **Second and Third Trimester Vaginal Bleeding**, a pelvic ultrasound is considered “Usually Appropriate.” The primary goal is to assess for placenta previa, where the placenta covers or is near the internal cervical os, which is a common cause of bleeding. The anatomy scan protocol is perfectly suited to evaluate placental location and rule out this and other potential causes. The ACR notes that fetal MRI is not a first-line tool for this indication but may be used to clarify suspected fetal anomalies or complex placental issues found on ultrasound.

7. How Much Radiation Does an Obstetric Ultrasound Deliver?

This is a common and important question from patients. An obstetric ultrasound delivers an effective radiation dose of 0 mSv.

Ultrasound imaging does not use ionizing radiation. Instead, it uses high-frequency sound waves to generate images. This is why it is the primary imaging modality used throughout pregnancy. There is no radiation dose to the mother or the fetus.

8. US Obstetric Anatomy Scan Protocol — Key Views and Measurements

The success of an anatomy scan hinges on a standardized, comprehensive protocol. The goal is to systematically evaluate every major fetal structure and the maternal environment. The exam is typically performed transabdominally with a 2-5 MHz curved array transducer, with the patient supine. A full bladder is not necessary and can actually distort the view of the lower uterine segment and cervix.

The protocol is a systematic survey. Below is a table summarizing the key components and their purpose.

Common protocol pitfalls: Performing the scan too early (before 18 weeks) can limit visualization of key structures due to fetal size. Performing it too late can be challenging due to acoustic shadowing from ossified bones and a more crowded fetal position. Missing the outflow tract views is a common error that can lead to missed cardiac anomalies.

7. The 3-Months-Free Residents Offer

3+ months free for radiology residents and fellows

Look like a rockstar on your reports — dictate positive findings in free form, and the AI generates a structured report using ACR + SIR templates with the appropriate Clinical Decision Support (CDS) firing automatically. All we ask is feedback so we can keep improving the product for trainees.

Signup is simple. No credit card. No long forms. To get started, just provide these three items:

1. Your PGY year (e.g., PGY-2, PGY-4)
2. Your training type (radiology residency or specific fellowship — IR, body, MSK, neuro, peds, breast, nucs)
3. Your training program / hospital name

You can also include an optional institutional email. Ready to give it a try? Apply for the residents free-access program here.

8. Frequently Asked Questions

Is GigHz Precision AI HIPAA-compliant?

Yes. The platform is designed for de-identified workflows by default. It processes the clinical content of your dictation without requiring or storing patient-identifying information (PII/PHI). All data is handled within a secure, HIPAA-compliant environment.

Do I need my hospital’s IT department to set this up?

No. GigHz Precision AI is a secure, browser-based tool. There is no software to install on hospital machines. It works on any modern web browser, including on the call-room computer, your personal laptop, or even an iPad.

Does it work with PowerScribe or other voice recognition software?

Yes. It’s designed to complement your existing dictation system, not replace it. You can dictate into your usual microphone and PACS setup. The AI works in the background to help structure the output, which you can then copy and paste into your final report in the EMR.

Can I use it on my phone or iPad?

Yes, the platform is fully responsive and works on mobile devices and tablets. This is particularly useful for reviewing or editing reports on the go or using it on a tablet in the reading room.

Can I customize the templates?

Yes. While the system comes pre-loaded with templates based on ACR and other society guidelines, you can customize them to match your institution’s specific formatting preferences or your personal style.

What happens after my residency or fellowship ends?

We offer continuity plans for graduating trainees who want to continue using the platform in their practice. Your customized templates and settings can be carried over, so you don’t lose your work.

Free GigHz Tools That Pair With This Article

Three free tools that complement the material above:

• ACR Appropriateness Criteria Lookup — Type an indication or clinical scenario in plain language and get the imaging studies the ACR rates for it, with adult and pediatric radiation levels. Built directly from 297 ACR topics, 1,336 clinical variants, and 15,823 procedure ratings.
• GigHz Imaging Protocol Library — A searchable library of 131 imaging protocols with the physics specs surfaced and the matching ACR Appropriateness Criteria alongside. Plain-English narratives readable in 60 seconds, organized by modality.
• GigHz Radiation Dose Calculator — Pick the imaging studies a patient has had and see total dose in millisieverts (mSv) with comparisons to natural background radiation, transatlantic flights, and chest X-rays. Useful for shared decision-making.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 7, 2026