Gender At 13-Week Ultrasound- Is It Accurate? | Worth A Guess

You’re 13 weeks along, you’ve got an ultrasound on the screen, and that one question starts buzzing in your head: “Can they tell yet?” It’s normal to want a straight answer. It’s also normal to hear a confident “boy” or “girl” and still wonder if it’s a real read or a good-sounding guess.

Here’s the honest deal: at 13 weeks, fetal sex can sometimes be identified correctly, yet it’s not a lock. Timing, view angle, baby position, and the sonographer’s ability to capture the right plane can swing the call.

What A 13-Week Ultrasound Can Tell About Fetal Sex

At 13 weeks, the scan is usually aimed at dating the pregnancy, checking basic anatomy, and measuring structures used in first-trimester screening. Sex can be assessed during this window, but it often relies on a single feature: the genital tubercle.

The genital tubercle is the small structure that later develops into external genitalia. On a good mid-sagittal view (a true side profile), its angle relative to the spine can lean male or female. That approach is often called “genital tubercle angle” in clinical studies.

Research has found that accuracy improves fast between 11 and 13 weeks. A well-known early study from the Fetal Medicine Foundation reported rising accuracy with gestational age and described very high accuracy by 13 weeks when the view was suitable for assessment, with earlier weeks showing more misses and more “can’t tell” results (Fetal Medicine Foundation paper on first-trimester sex determination).

That last part matters: “when the view was suitable.” Real appointments are messy. Babies curl up, spin, tuck their legs, or face away at the wrong time. A single still image that looks convincing can still be off by a few degrees, and a few degrees can flip the call.

Gender At 13-Week Ultrasound- Is It Accurate? What Changes The Odds

If your scan report or sonographer gives a sex prediction at 13 weeks, treat it like an early read that can be right, not a promise. The strongest predictors of a correct call are simple: correct gestational age, a clean side profile, and a steady baby position long enough to capture the right plane.

Accuracy also depends on what “accurate” means in the moment. Some clinics will only share a guess if the view is crystal clear. Others will share a best read even when the image is borderline. Those two styles can feel the same in the room, yet they don’t carry the same certainty.

A systematic review and meta-analysis published in 2024 reported that first-trimester ultrasound sex identification can be correct in a large share of pregnancies between 11 and 14 weeks, with sensitivity improving as gestational age increases (the paper pooled studies and found mid-80% accuracy in that window) (Systematic review on first-trimester ultrasound sex identification).

So yes, 13 weeks can be pretty good in the right hands with the right view. Still, it’s not the same as a mid-pregnancy anatomy scan, where external genital anatomy is more developed and easier to see.

Why 13 Weeks Can Still Be Wrong

Most wrong calls at 13 weeks come down to one of these: the wrong plane, a shadow, or a tubercle that’s still in a “neutral” position. In early development, small differences look big on a screen, then look different again when the angle shifts by a hair.

There’s also a timing trap. Someone might say “13 weeks,” but in ultrasound terms, 12+2 and 13+6 are not the same moment. A couple of days can change what’s visible, and it can change the confidence level of a careful reader.

Then there’s the human side. Even skilled sonographers and physicians work under time limits. If the baby won’t cooperate, they may have to move on. That’s not a lack of skill. It’s just real life in a clinic schedule.

How Sonographers Actually Make The Call

Most sex predictions at this stage come from a side-profile view that shows the spine and the genital tubercle. The reader is trying to avoid “almost side profile” images where the pelvis is slightly rotated. Rotation can make the tubercle look higher or lower than it is.

On top of angle, image quality matters. Early scans can be transabdominal or transvaginal. A transvaginal scan can give sharper detail early in pregnancy, though what’s used depends on clinic practice and what’s medically appropriate. Patient-facing guidance from RadiologyInfo describes how obstetric ultrasound is performed and what it is used for during pregnancy (RadiologyInfo obstetric ultrasound overview).

If you’re getting a sex guess from a boutique scan, ask who is performing it and what training they have. A pretty image is not the same thing as a clinical read.

Common Reasons You Might Hear “Not Sure Yet”

“Not sure yet” can feel frustrating, but it’s often the most careful answer in the room. A cautious reader would rather tell you they can’t see it than send you home with a confident call that flips later.

These are the most common blockers:

• Baby is curled tightly, with pelvis tucked.
• Legs are crossed or pressed together.
• Placenta position or maternal tissue makes the view less clear.
• The scan is being done early in the 13th week window.
• The fetus is rotating, so the “perfect plane” never holds long enough.

If you got a “not sure,” it doesn’t mean anything is wrong. It usually means the reader took accuracy seriously.

Accuracy Boosters You Can Try Before The Scan

You can’t control the baby’s pose, but you can make the appointment smoother. Keep expectations realistic, then do a couple of small things that sometimes help:

• Arrive hydrated unless your clinic gave different instructions.
• Wear two-piece clothing so setup is quick and comfortable.
• If you’re nervous, say so. A calmer pace can help get better images.

During the scan, you can also ask the right kind of question. Instead of “Boy or girl?” try: “Is the view clear enough for a confident call, or is it still a guess?” That invites honesty without putting anyone on the spot.

Table Of Factors That Affect A 13-Week Sex Prediction

The table below lays out what most often shifts a 13-week prediction toward “pretty solid” or “could flip.”

Factor	What It Changes	What You Can Ask Or Do
Gestational age within week 13	Later days can show clearer genital development	Ask how far along you measure on scan, not just by dates
True side-profile plane	Rotation can tilt the tubercle and flip the read	Ask if the image is a mid-sagittal view
Baby position	Legs tucked or crossed can hide the area	Ask if movement could improve visibility, then allow a few minutes
Scan type (abdominal vs vaginal)	Early detail can be sharper with a vaginal approach	Ask what method is being used and why
Image quality and zoom	Shadows or blur can create false “signs”	Ask if the reader can capture a still image with clear landmarks
Reader experience with early sex reads	Pattern recognition improves with volume and training	Ask if the clinic routinely offers sex guesses at this stage
Fetus angle at the moment of capture	A slight pelvis tilt changes perceived tubercle angle	Ask if multiple views matched the same conclusion
Clinic policy on sharing “best guess”	Some clinics share only high-confidence calls	Ask what level of certainty they require before saying it out loud

What To Expect At The 18–22 Week Anatomy Scan

If you want the clearest ultrasound answer, the mid-pregnancy anatomy scan is the usual moment. External genital anatomy is more developed, and the sonographer has more time to check multiple angles.

In many health systems, this scan is scheduled near 20 weeks. The NHS explains the purpose and timing of the 20-week screening scan (also called the anomaly scan), including what it checks for during pregnancy (NHS guidance on the 20-week screening scan).

Sex is often visible at this stage, though clinics vary on whether they offer it routinely. Some places treat it as optional info and only share it if you ask, since the medical aim of the scan is anatomy review.

Blood Testing Options That Can Report Fetal Sex Earlier

If you want earlier information and you’re already doing prenatal screening, you may hear about cell-free DNA screening (often called NIPT). This is a screening test, not a diagnostic test, but it can report fetal sex in many settings because it looks at fetal DNA fragments in maternal blood.

ACOG describes cell-free DNA as the most sensitive and specific screening test for common fetal aneuploidies, while also noting that screening can still have false positives and false negatives (ACOG current guidance on noninvasive prenatal testing).

If fetal sex knowledge is tied to a sex-linked condition in your family, ask your obstetric clinician how they want to confirm it. In that setting, a screening result may not be enough on its own.

Table Comparing Timing And Certainty Across Methods

Different tools answer different questions. This table keeps it simple and practical.

Method	Typical Timing	What It Can Tell About Sex
13-week ultrasound guess	11–14 weeks	Can suggest male or female when the view is clear; can be wrong
Anatomy scan ultrasound	18–22 weeks	Often clearer visual identification based on developed anatomy
Cell-free DNA screening (NIPT)	Often from 10 weeks onward	May report sex chromosomes; still a screening test, not diagnostic
Chorionic villus sampling (CVS)	Often 10–13 weeks	Diagnostic chromosome testing that can determine sex chromosomes
Amniocentesis	Often 15+ weeks	Diagnostic chromosome testing that can determine sex chromosomes

How To Handle A 13-Week Result Without Overthinking It

If you got a confident “boy” or “girl” at 13 weeks, enjoy it, then leave a little space for the possibility of a flip. If you’re planning a reveal party or ordering personalized items, waiting until the anatomy scan lowers the chance of a costly redo.

If you got a “maybe,” treat it as a fun detail, not a fact. If you got a “can’t tell,” that’s often the most careful outcome, and it can save you a lot of second-guessing later.

One practical way to frame it is to ask the clinic for their wording. Some practices will write “appears male/female” when they feel good about it, and they’ll avoid that phrasing when the view was borderline. The exact language varies, so it’s worth asking what terms they use.

When Accuracy Matters For Medical Reasons

Most people ask out of curiosity. Sometimes there’s a medical reason, like a family history of a sex-linked genetic condition. In that situation, getting the answer right can shape screening and next steps.

If you’re in that group, don’t rely on an early ultrasound guess. Ask your obstetric clinician what confirmation path fits your situation. Screening tests, diagnostic tests, and imaging each play a different role, and the right choice depends on your own medical picture.

Smart Questions To Ask At Your Next Appointment

If you want clarity without awkwardness, these questions work well:

• “Was the view a true side profile, or was the pelvis rotated?”
• “Is this a high-confidence call, or a best read?”
• “If it’s a guess, what’s the main reason it could flip?”
• “Will the anatomy scan be the point where you confirm it?”

You’re not grilling them. You’re asking for context. Most clinicians appreciate that.

What This Means If You’re Planning A Reveal

If you’re set on an early reveal, build in a backup plan. Keep decorations and clothing flexible. Save the name sign for later. If you’re ordering a custom cake topper, wait until the anatomy scan or choose neutral wording.

If you’d rather keep it calm, a simple plan works: treat 13 weeks as a hint, then treat 18–22 weeks as the confirmation point. That approach fits how most clinics view the timeline of visibility.

Takeaway You Can Trust

A 13-week ultrasound can be right about fetal sex, and research shows accuracy rises sharply by this stage when the correct view is captured. Still, real-world scans don’t always offer that perfect view. If you want the clearest ultrasound answer, the mid-pregnancy anatomy scan is the more reliable moment. If fetal sex knowledge is tied to medical decisions, ask your obstetric clinician about confirmation with the testing path that fits your situation.