US Obstetric First Trimester — Dictation, Appropriateness, and Dose for Residents
First Trimester Obstetric Ultrasound — The On-Call Dictation Template
Stat from the ED. 24-year-old G1P0 at 8 weeks by LMP with vaginal bleeding and pelvic pain. Beta-hCG is 3,000 mIU/mL. The ED team needs to know if it’s an ectopic, the OB team wants to know if it’s viable, and your attending expects you to nail the dating with Crown-Rump Length (CRL) and comment on the adnexa. This is one of the most common and highest-stakes studies you’ll read on call. Getting the key elements right, in the right order, is non-negotiable.
When I was a resident, the pressure on these reads was real. You’re not just looking for a heartbeat; you’re establishing the foundation for the entire pregnancy’s care. This guide is built to give you the structure and confidence to dictate a clean, comprehensive first-trimester OB ultrasound report every time. For more guides like this, check out the residents and fellows resource hub, which has free calculators and references for trainees.
What a First Trimester Obstetric Ultrasound Covers and What Attendings Look For
A first-trimester obstetric ultrasound (performed at or before 13 weeks and 6 days) is the definitive study for early pregnancy assessment. Its primary goals are to confirm the location and viability of a pregnancy, establish an accurate gestational age, and identify any immediate threats or major abnormalities.
Your attending is looking for a report that systematically answers these key clinical questions:
- Location: Is there an intrauterine pregnancy (IUP)? Are there features of an ectopic pregnancy?
- Viability: Is there a yolk sac? Is there an embryo? Is there fetal cardiac activity, and what is the rate (documented with M-mode)?
- Dating: What is the Crown-Rump Length (CRL), and what is the corresponding estimated gestational age (EGA)? How does this compare to the LMP-based dating?
- Number: Is it a singleton or multiple gestation? If multiples, what is the chorionicity and amnionicity (e.g., dichorionic-diamniotic)?
- Uterus and Adnexa: Are there uterine anomalies like fibroids? Is there a corpus luteum cyst? Is there an adnexal mass concerning for ectopic? Is there free fluid?
- Screening (if applicable): If the study is between 11+0 and 13+6 weeks, what is the nuchal translucency (NT) measurement?
A clear report addresses each of these points, leaving no ambiguity for the referring clinician.
Radiology Report Template for a First Trimester Obstetric Ultrasound
Before jumping into the template, here are the key principles to keep in your head during the read. These are the numbers and signs that drive your impression.
- Discriminatory Zone: A gestational sac should be visible transvaginally when beta-hCG is ~1500-2000 mIU/mL. An empty uterus above this level is highly suspicious for an ectopic pregnancy.
- Viability Milestones: A yolk sac should be seen by 5.5-6 weeks. An embryo with cardiac activity should be seen by 6-6.5 weeks.
- First Trimester Loss Criteria: CRL ≥7 mm without cardiac activity indicates embryonic demise. A mean sac diameter (MSD) ≥25 mm without an embryo is an anembryonic gestation.
- Dating: CRL is the most accurate biometric (±5-7 days). Re-date the pregnancy if the CRL-based age differs from the LMP-based age by more than 5-7 days.
- Chorionicity: This must be determined in the first trimester. Look for the “lambda/twin peak” sign (dichorionic) or the “T sign” (monochorionic).
- Cardiac Activity: Always use M-mode, not spectral Doppler, to document the fetal heart rate. This minimizes thermal exposure to the embryo.
Technique
Transabdominal and transvaginal pelvic ultrasound was performed. Grayscale and color Doppler images were obtained. No ionizing radiation was used.
Findings
UTERUS: Anteverted/retroverted. Normal in size and morphology. No fibroids identified.
ENDOMETRIUM: [Describe endometrial thickness and appearance. Note presence or absence of gestational sac.]
INTRAUTERINE PREGNANCY:
A single live intrauterine pregnancy is identified.
Gestational Sac: Present. Mean sac diameter is [__] mm.
Yolk Sac: Present/Absent.
Embryo: Present. Crown-rump length (CRL) is [__] mm, corresponding to an estimated gestational age of [__] weeks and [__] days.
Cardiac Activity: Present. The fetal heart rate is [__] bpm as documented by M-mode.
Nuchal Translucency (if 11+0 to 13+6 weeks): [__] mm.
Subchorionic Hemorrhage: [Present/Absent. If present, describe size and location.]
ADNEXA:
Right Ovary: Measures [__ x __ x __] cm. [Describe findings, e.g., “Contains a corpus luteum cyst measuring __ cm.” or “Normal in appearance.”]
Left Ovary: Measures [__ x __ x __] cm. [Describe findings.]
Adnexal Mass: No suspicious adnexal mass is identified.
Fallopian Tubes: Not visualized, without evidence of hydrosalpinx or ectopic pregnancy.
CUL-DE-SAC: No free fluid.
Impression
1. Single live intrauterine pregnancy.
– Estimated gestational age of [__] weeks and [__] days by crown-rump length.
– Fetal heart rate is [__] bpm.
2. [No evidence of ectopic pregnancy.]
3. [Other findings, e.g., “Small subchorionic hemorrhage.” or “Right ovarian corpus luteum cyst.”]
Where to Find Other Free Radiology Report Templates
Building a personal library of high-quality templates is a must during training. While you can create your own macros, two great free repositories exist that are curated by radiologists for radiologists.
- RadReport.org: Maintained by the RSNA, this is the most comprehensive library out there. It has standardized templates for nearly every study you can think of, aligned with best practices. (https://radreport.org/)
- Radiology Templates (AU): This is an excellent, user-friendly site maintained by Australian radiologists. It’s a great alternative with clean, practical templates. (https://www.radiologytemplates.com.au/home-page/)
Bookmark both. They’re invaluable when you encounter a rare study or just want to see how others structure a complex report.
The Next-Level Move: AI-Assisted Structured Reporting
The biggest friction point in reporting isn’t knowing the findings; it’s translating them into a perfectly structured report that your attending expects, especially under pressure. Instead of meticulously editing a static macro, you can dictate your positive findings in free form and let an AI tool handle the rest.
Tools like GigHz Precision AI are designed for this exact workflow. You speak your findings naturally—”single live IUP, CRL of 15 mm for 8 weeks 0 days, heart rate 160, small subchorionic hemorrhage”—and the platform generates a complete, structured report using pre-loaded ACR templates. It also helps surface relevant Clinical Decision Support (CDS) criteria when applicable, though no specific CDS popup fires for this particular first-trimester ultrasound template. This approach helps streamline the dictation process, ensuring key elements aren’t missed while reducing the manual effort of template management.
When Should You Order a First Trimester Obstetric Ultrasound? ACR Appropriateness Criteria
The American College of Radiology (ACR) provides evidence-based guidelines to help clinicians choose the right imaging study. For a patient presenting with first-trimester vaginal bleeding, the guidance is clear.
Per the ACR Appropriateness Criteria for First Trimester Vaginal Bleeding, a pelvic ultrasound—including both transabdominal and transvaginal approaches—is rated as Usually Appropriate. This is the definitive initial imaging test to determine the presence, location, and viability of a pregnancy and to identify potential causes of bleeding like a subchorionic hemorrhage or an ectopic pregnancy.
Alternatives are limited in this clinical scenario. Serial quantitative beta-hCG measurements are a complementary biochemical assessment, not a replacement for imaging. MRI is rarely used in the first trimester for bleeding but may have a role if sonographic windows are suboptimal or complex pathology is suspected, though this is uncommon.
How Much Radiation Does a First Trimester Obstetric Ultrasound Deliver?
A first-trimester obstetric ultrasound delivers an effective radiation dose of 0 mSv. The study uses sound waves, not ionizing radiation, making it completely safe for both the mother and the developing embryo. This is a critical point of reassurance for patients and referring providers.
The lack of radiation is why ultrasound is the sole imaging modality for routine pregnancy evaluation. There are no dose-reduction protocols to consider because there is no dose to begin with. The main safety consideration is minimizing thermal exposure by using M-mode instead of spectral Doppler to document the fetal heart rate in the first trimester.
First Trimester Obstetric Ultrasound Imaging Protocol — Technique and Key Parameters
The first-trimester OB ultrasound protocol is a two-part exam designed to maximize diagnostic information, starting with a broad overview and moving to a high-resolution evaluation. The exam typically begins with a transabdominal approach to get a general survey of the pelvis, followed by a transvaginal approach for detailed views of the pregnancy and adnexa.
The table below outlines the key technical parameters for each component of the study.
| Phase / Technique | Transducer | Patient Prep / Approach | Key Purpose |
|---|---|---|---|
| Transabdominal Survey | Curved array (2-5 MHz) | Full bladder (acoustic window) | Global view of uterus, adnexa, and cul-de-sac. Identify large abnormalities. |
| Transvaginal Imaging | Endovaginal probe (5-10 MHz) | Empty bladder | High-resolution views of gestational sac, yolk sac, embryo, and ovaries. Essential for early gestations. |
| M-mode | Endovaginal probe | Focused on embryo | Accurately document fetal heart rate with low thermal index (TI). |
| Color/Spectral Doppler | Endovaginal probe | Used sparingly on adnexa | Evaluate for “ring of fire” in suspected ectopic. Avoid use on the embryo due to higher thermal index. |
A common protocol pitfall or variation is the order of operations. While many centers start with a transabdominal scan, some will proceed directly to transvaginal imaging if the patient is known to be in very early gestation (e.g., <7-8 weeks), as the transabdominal views are unlikely to be diagnostic.
The 3-Months-Free Offer for Radiology Residents and Fellows
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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 firing automatically. This lets you focus on the images, not on hunting for macros or manually structuring every sentence.
All we ask in return is your feedback so we can keep improving the product for trainees. The signup process is simple, with no credit card and no long forms. To get started, just provide these three items:
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If you’re ready to streamline your reporting workflow, you can apply for the residents free-access program and get set up quickly.
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.
Frequently Asked Questions
Is it HIPAA-compliant?
Yes. The platform is designed for de-identified workflows by default. You dictate the clinical findings, not the patient’s name, MRN, or date of birth. It operates on the anonymized clinical data within your dictation to generate a structured report, maintaining patient privacy.
Do I need my hospital’s IT department to set it up?
No. It’s a browser-based tool that works on any modern computer, including the workstations in the reading room or your personal laptop or iPad. There is no software to install and no complex integration required with the hospital EMR or PACS.
Does it work with PowerScribe or other dictation systems?
Yes. You can use it alongside your existing dictation system. Most residents generate the structured report in the browser, then simply copy and paste the final text into PowerScribe or Fluency. It complements your existing workflow rather than replacing it.
Can I use it on my phone or iPad on call?
Absolutely. The platform is web-based and responsive, so you can access it on a tablet or even a phone to quickly look up a template or generate a report structure when you’re away from a dedicated workstation.
Can I customize the templates?
Yes. While the system comes pre-loaded with standardized templates from governing bodies like the ACR and SIR, you have the ability to create, modify, and save your own templates to match your personal or institutional preferences.
What happens after I finish my residency or fellowship?
The free access program is specifically for trainees. After you graduate, you can transition to a standard attending-level subscription to continue using the service in your practice.
Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 7, 2026
