Category: Patient Guide

Many parents feel worried when they hear during an NT scan:

👉 “The baby is difficult to see today.”
👉 “We may need more time.”
👉 “The image isn’t very clear.”

But in many cases, this does not mean something is wrong with the baby.

There are several reasons why NT ultrasounds can sometimes be more challenging than expected — and one of them is something surprisingly common:

👉 Bowel gas.

What Is an NT Ultrasound?

NT (Nuchal Translucency) ultrasound is usually performed between 11 and 13 weeks of pregnancy.

The purpose is to measure the fluid at the back of the baby’s neck and assess the risk of certain chromosomal abnormalities.

Because the baby is still very small at this stage, obtaining the perfect image can sometimes be technically difficult.

Why Can NT Scans Be Difficult?

Several factors affect ultrasound image quality, including:

• Fetal position
• Maternal body habitus
• Uterine position
• Early gestational age
• Bowel gas

Even a small change in angle or movement can affect the NT measurement.

Can Bowel Gas Really Affect the Scan?

👉 Yes — it absolutely can.

Ultrasound works by sending sound waves through the body.

Gas inside the intestines can interfere with those sound waves, which may:

• Reduce image clarity
• Create shadowing
• Block parts of the image
• Make measurements more difficult

This is especially noticeable during early pregnancy scans because the fetus is still very small.

Fetal Position Matters Too

Sometimes the baby may be:

• Facing downward
• Curled up
• Moving constantly
• Positioned too close to the uterine wall

In these situations, the sonographer may ask you to:

• Walk around
• Change position
• Wait and try again later

This is actually very common during NT exams.

A Difficult Scan Does Not Always Mean a Problem

One important thing to remember is:

👉 A technically difficult ultrasound is not the same as an abnormal ultrasound.

In many cases, the difficulty comes from temporary factors such as:

• Gas
• Position
• Angle
• Movement

—not because something is wrong with the baby.

What Can Help Before the Scan?

Depending on your clinic’s instructions, it may help to:

• Stay relaxed
• Avoid excessive abdominal tension
• Follow bladder instructions carefully
• Move around if asked during the scan

Every pregnancy — and every ultrasound — is different.

Final Thoughts

NT ultrasounds are important examinations, but they are also highly dependent on fetal position and imaging conditions.

If your scan takes longer than expected or the images are difficult to obtain, try not to panic immediately.

Sometimes it’s simply the baby’s position… or even bowel gas.

And that’s more common than many people realize.

There are moments in healthcare that stay with you long after the day ends.

Recently, during a 3D ultrasound scan, I explained to a patient that the baby’s position made the images difficult to obtain.
The baby was facing downward, which can make detailed facial views very challenging.

I tried to explain the situation honestly and suggested trying again later if needed.

But the patient felt that I sounded too negative.

After the exam, I kept replaying the conversation in my mind.

Did I sound too serious?
Could I have explained it more gently?
Did my words increase her anxiety instead of reassuring her?

As sonographers, we focus so much on obtaining the best possible images that sometimes we forget how emotional these moments are for parents.

For us, fetal position is a technical limitation we see every day.
But for parents, this may be a long-awaited moment filled with excitement and worry.

That day reminded me of something important:

👉 Medical information is not only about accuracy.
👉 It’s also about how patients emotionally receive our words.

At the same time, I also realized something else.

Healthcare workers are human too.

Most sonographers truly want the best for their patients.
Even on busy or difficult days, we try our best to provide safe and accurate examinations.

Sometimes communication is imperfect.
Sometimes emotions get mixed with stress and expectations.

But every difficult interaction teaches us something.

For me, this experience became a reminder to balance honesty with reassurance — and to remember the emotional side of ultrasound, not only the technical side.

Many parents feel reassured after a normal NT scan.

But then comes the 20-week anatomy scan…
and sometimes, something unexpected is mentioned.

👉 This can be confusing — and scary.

So what’s the difference between these two important ultrasounds?

📅 What Is the NT Scan?

The NT scan (Nuchal Translucency scan) is done between 11 and 13+6 weeks of pregnancy.

It measures the fluid at the back of your baby’s neck.

👉 The main goal is to:

• Screen for chromosomal conditions (like Down syndrome)
• Assess early risk

👉 Important:
This is a screening test — not a diagnostic one.

🔍 What Is the 20-Week Anatomy Scan?

The 20-week anatomy scan (anomaly scan) is done between 18 and 22 weeks.

👉 This scan looks at:

• Brain
• Heart
• Spine
• Abdomen
• Kidneys
• Limbs

👉 In simple terms:
It checks how your baby is actually formed.

⚖️ Key Differences (Simple Comparison)

NT Scan	Anatomy Scan
Done at 1113 weeks	Done at 1822 weeks
Screening test	Structural evaluation
Measures fluid (NT)	Looks at organs
Estimates risk	Detects physical findings

👉 Think of it like this:

• NT scan = risk check
• Anatomy scan = detailed inspection

❗ “My NT Scan Was Normal… So Why Did Something Show Up Later?”

This is one of the most common questions.

👉 And the answer is:

Because the two scans look for different things.

🧬 Why This Happens

• Some structures are too small to evaluate early
• Certain conditions develop or become visible later
• NT scan focuses on markers, not anatomy

👉 So even with a normal NT scan,
something may still be seen at 20 weeks.

💛 What It Usually Means

👉 Most findings on the anatomy scan are:

• Minor
• Temporary
• Or simply need follow-up

👉 Very important:

Most of the time, everything turns out to be normal.

👩‍⚕️ From a Sonographer’s Perspective

Sometimes, what looks “abnormal” at first is simply:

• A difficult angle
• Baby position
• Or an incomplete view

👉 That’s why repeat scans are very common.

🧾 What Should You Do?

If something is mentioned:

• Don’t panic
• Ask what exactly was seen
• Follow your provider’s recommendations
• Attend any follow-up scans

👉 Information + time usually brings clarity.

📌 Final Thoughts

A normal NT scan is a very reassuring sign.

And even if something comes up later,
👉 it does not automatically mean something is wrong.

These scans work together to give the best picture of your baby’s development.

The 20-week anatomy scan is one of the most important milestones in pregnancy.

👉 This is the ultrasound where doctors carefully examine every major organ of your baby.

For many parents, it’s exciting — but also a little nerve-wracking.

In this guide, you’ll learn exactly:

• What doctors are looking for
• How the scan works
• What “normal” really means
• And what happens if something looks unclear

📅 What Is the 20-Week Anatomy Scan?

The 20-week anatomy scan (also called the mid-pregnancy ultrasound or anomaly scan) is a detailed ultrasound performed between 18 and 22 weeks of pregnancy.

Its purpose is to:

• Check your baby’s growth
• Examine the structure of organs
• Identify any potential abnormalities
• Confirm your due date
• Evaluate the placenta and amniotic fluid

👉 It is a routine scan — but also one of the most detailed ones you’ll have.

⏰ When Is It Done?

Most providers schedule this scan between 18 and 22 weeks, with 20 weeks being ideal.

At this stage:

• The baby is large enough to see clearly
• Organs are developed enough to evaluate
• There’s still time for follow-up if needed

⏳ How Long Does It Take?

The scan usually takes 30 to 60 minutes.

Sometimes it takes longer if:

• The baby is in a difficult position
• Certain structures are hard to see
• Extra images are needed

👉 From a sonographer’s perspective:
Sometimes we spend more time simply because your baby isn’t cooperating — not because something is wrong.

🔍 What Do Doctors Check?

This is the most detailed ultrasound of your pregnancy.

🧠 Brain and Head

Brain structures (ventricles, cerebellum, corpus callosum)

Skull shape and size

Face (lips, nose, eyes)

❤️ Heart

Four-chamber view

Outflow tracts

Heart rate and rhythm

👉 The heart is one of the most important — and sometimes most challenging — parts of the scan.

🫁 Chest and Lungs

Lung development

Diaphragm integrity

🍼 Abdomen

Stomach (checking swallowing)

Abdominal wall closure

Bowel

🫘 Kidneys and Bladder

ㅇㅇKidneys (size and presence)
Bladder filling and emptying


🦴 Spine and Limbs
Spine alignment (checking for spina bifida)

Arms, legs, hands, and feet

Bone measurements

🤰 Placenta and Amniotic Fluid

• Placenta location
• Amniotic fluid levels
• Umbilical cord

👶 Can You Find Out the Baby’s Sex?

Yes — if you want to know.

At 20 weeks, the baby’s sex is usually visible.

However:

• It’s not always 100% certain
• Baby position matters
• Some parents prefer a surprise

🧾 How to Prepare

Preparation is simple:

• Drink water beforehand
• Wear comfortable clothing
• Bring a support person (if allowed)
• Bring previous scan records

👉 No special preparation is required.

⚠️ What If Something Looks Unusual?

This is the part most parents worry about.

👉 Here’s the key point:

Most anatomy scans are completely normal.

If something is mentioned, it could be:

• Soft marker → usually minor and often harmless
• Structural finding → may need further evaluation
• Incomplete view → baby position prevented a clear image

👉 Follow-up scans are very common and do not automatically mean something is wrong.

❓ Common Questions

Can this scan detect Down syndrome?

It can identify certain markers, but it is not a diagnostic test. Additional testing may be recommended if needed.

Is ultrasound safe?

Yes. Ultrasound uses sound waves, not radiation, and is considered safe.

What if the baby doesn’t cooperate?

You may be asked to:

• Change position
• Walk around
• Eat something

Sometimes, a repeat scan is scheduled.

Will I get pictures?

Most clinics provide printed or digital images — ask in advance.

📌 What Happens After the Scan?

After the exam:

• The doctor reviews the images
• Results are usually discussed the same day or shortly after
• Most scans are normal

If something needs follow-up, your provider will guide you clearly.

💛 Final Thoughts

The 20-week anatomy scan is a powerful and reassuring moment in your pregnancy.

It allows doctors to carefully check your baby’s development — and in most cases, everything looks exactly as it should.

👉 Go in informed, ask questions, and try to enjoy the experience.

You’re getting one of the most detailed looks at your baby before birth.

자궁경부 길이, 어떤 초음파가 더 정확할까요?

ㅇ

👀 “복부로 봤는데 정상이라던데요?”




산모분들이 정말 많이 하시는 질문입니다


👉 “복부초음파로 봤으면 괜찮은 거 아닌가요?”


👉 결론부터 말씀드리면
👉 상황에 따라 다르지만, 정확도는 TVS가 더 높습니다


📊 TAS vs TVS 한눈에 비교

구분	TAS 복부초음파	TVS 질 초음파
정확도	보통	매우높음
검사방법	배위에서	질내부
방광필요	필요 (full bladder)	필요없음
장점	접근편함	가장정확
단점	과대평가 가능	거부감

📏 왜 TVS가 더 정확할까요?

👉 핵심 3가지

1️⃣ 거리 차이

• TAS: 멀리서 봄
• TVS: 바로 옆에서 봄

👉 해상도 차이 발생

2️⃣ 방광 영향

• TAS는 방광이 차야 보임
  👉 이때 자궁경부가 길어 보일 수 있음

👉 즉,

실제보다 “더 길게 측정되는 경우” 있음

3️⃣ Funnel / Dynamic 변화

• TVS: funneling, shortening 잘 보임
• TAS: 놓치는 경우 많음

❗ 그래서 중요한 포인트

👉 이거 핵심입니다

✔ TAS에서 정상 → 안심 가능 (기본 screening)

❗ BUT

✔ 의심되면 → TVS로 반드시 확인

🧠 실제 임상 기준

👉 보통 이렇게 갑니다

• 1차: TAS로 확인
• 애매하다 / 짧아 보인다 → TVS

👉 특히 이런 경우

• 이전 조산 경험
• 복통 / 수축
• 경부 짧아 보임

👉 무조건 TVS

💡 한줄 정리

TAS는 “대략적인 확인”

TVS는 “정확한 진단”

TAS vs TVS: Which is more accurate for cervical length?

👉 Transvaginal ultrasound (TVS) is more accurate

Why?

• Closer to the cervix → better resolution
• No bladder distortion
• Better detection of funneling

👉 TAS may overestimate cervical length

Key takeaway

TAS = screening

TVS = gold standard

Pulmonary embolism (PE) is one of the leading causes of maternal mortality.

When PE is suspected during pregnancy, rapid diagnosis is critical.

However, many patients worry:

“Is CT safe? Should MRI be used instead?”

Understanding imaging choices helps clarify risk and safety.

Why Is Pulmonary Embolism a Concern in Pregnancy?

Pregnancy increases the risk of blood clots due to:

• Hypercoagulable state
• Reduced venous return
• Vascular compression by the uterus

Symptoms such as:

• Sudden shortness of breath
• Chest pain
• Tachycardia

Should never be ignored.

Imaging Options for PE in Pregnancy

1️⃣ CT Pulmonary Angiography (CTPA)

CTPA is widely used because it:

• Provides rapid diagnosis
• Has high sensitivity and specificity
• Is widely available in emergency settings

Fetal radiation exposure from chest CT is generally low because the uterus is outside the primary radiation field.

2️⃣ MRI for Pulmonary Embolism

MRI avoids ionizing radiation.

However:

• MRI is less commonly used for acute PE diagnosis
• Availability may be limited
• Diagnostic accuracy for PE is variable compared to CT

MRI is not typically first-line for suspected pulmonary embolism.

3️⃣ Ventilation-Perfusion (V/Q) Scan

In some centers, a V/Q scan may be considered.

Radiation exposure to the fetus can be comparable to or sometimes lower than CT, depending on protocol.

Choice depends on:

• Chest X-ray findings
• Institutional protocol
• Maternal clinical stability

Is CT Safe During Pregnancy?

For suspected PE:

• Chest CT delivers relatively low fetal radiation dose
• Maternal breast exposure is higher than fetal exposure
• Delayed diagnosis poses greater risk than imaging

Untreated pulmonary embolism is life-threatening.

What Do Guidelines Recommend?

Most clinical guidelines support:

• Risk stratification
• Imaging when PE is strongly suspected
• CT or V/Q scan depending on local protocol

MRI is generally not first-line for acute PE.

Counseling Perspective

Patients often focus only on radiation risk.

It is important to explain:

• Maternal survival is the priority
• Fetal radiation dose from chest CT is low
• Missing a pulmonary embolism is far more dangerous

Rapid, evidence-based imaging protects both mother and baby.

Final Thoughts

When pulmonary embolism is suspected during pregnancy, imaging should not be delayed.

CT pulmonary angiography is often the preferred diagnostic tool due to speed and accuracy.

MRI is not typically first-line for PE diagnosis.

The greater risk is untreated embolism — not appropriate imaging.

Hearing that you may need a CT scan during pregnancy can be frightening.

Many patients immediately ask:

“Will the radiation harm my baby?”

Understanding radiation dose, gestational timing, and medical necessity helps clarify real risk versus perceived risk.

Does a CT Scan Expose the Baby to Radiation?

Yes — CT scans use ionizing radiation.

However, risk depends on:

• Body area scanned
• Radiation dose (mGy)
• Gestational age
• Distance between the uterus and the scan field

Not all CT scans carry the same fetal exposure.

CT of the Head or Chest

When the CT scan is performed on:

• Head
• Neck
• Chest

Fetal radiation exposure is usually very low, often below harmful thresholds.

Scatter radiation may reach the uterus, but typically at minimal levels.

Abdominal or Pelvic CT

CT scans involving the abdomen or pelvis result in:

• Higher direct fetal radiation exposure
• Greater theoretical risk

Even then, most diagnostic CT scans deliver doses below levels associated with severe fetal harm.

What Radiation Dose Is Considered Risky?

Estimated fetal radiation effects:

• <50 mGy: No measurable increase in fetal anomalies
• 50–100 mGy: Slight increase in theoretical risk
• 100 mGy: Higher concern for developmental effects

Most single diagnostic CT scans remain below these thresholds.

Is CT Ever Necessary During Pregnancy?

Yes.

CT scans may be necessary in emergencies such as:

• Trauma
• Pulmonary embolism
• Severe abdominal pain
• Suspected life-threatening conditions

Maternal stabilization is the priority — untreated maternal illness may pose greater risk than imaging.

Are There Safer Alternatives?

Whenever possible:

• Ultrasound is preferred
• MRI without contrast may be considered

However, CT should not be delayed if it is medically necessary.

Counseling Perspective

Patients often equate “radiation” with inevitable harm.

It is important to explain:

• Dose matters
• Location matters
• Most diagnostic CT scans carry low fetal risk
• Delaying critical imaging can endanger both mother and baby

Balanced counseling prevents unnecessary fear while preserving safety.

Final Thoughts

A CT scan during pregnancy is not automatically dangerous.

Risk depends on radiation dose and body region scanned.

When medically indicated, CT imaging can be performed with careful risk assessment and appropriate shielding.

Maternal health and fetal safety must be evaluated together.

초음파에서 보이는 사지 소견 차이

두 염색체 이상 모두 사지 이상이 동반될 수 있지만,

양상이 다릅니다.

핵심은:

T18은 “고정된 변형”

T21은 “경미한 soft marker”

1️⃣ 손 소견 비교

🔴 Trisomy 18

• Persistent clenched hand
• Index finger overlapping 3rd finger
• 5th finger overlapping 4th finger
• 고정된 주먹 모양
• 움직임 거의 없음

👉 구조적 이상 + 기능적 고정

🟢 Trisomy 21

• Clinodactyly (5번째 손가락 휘어짐)
• Sandal gap (엄지-두번째 발가락 간격 증가)
• 경미한 단축

👉 손은 움직이고, 고정된 clenched 형태는 아님

2️⃣ 발 소견 비교

🔴 Trisomy 18

• Rocker-bottom foot
• Overlapping toes
• 발 모양 왜곡
• 종종 양측성

구조 자체가 변형된 모습

🟢 Trisomy 21

• Sandal gap
• 경미한 발가락 배열 변화
• 구조적 변형은 드묾

대개 soft marker 수준

3️⃣ 장골 길이 비교

🔴 Trisomy 18

• 성장 지연 동반
• 여러 구조 이상과 함께

🟢 Trisomy 21

• Isolated short femur 가능
• 다른 이상 없으면 단독 soft marker

4️⃣ 패턴 차이

항목	Trisomy 18	Trisomy 21
손	고정된clenched hand	clinodactyly
발	rocker-bottom foot	sandal gap
사지형태	구조적 변형	soft marker 중심
성장	심한 성장지연	경미~ 정상
동반기형	다장기 이상 흔함	심장 이상 흔함

🧠 임상적 사고

Trisomy 18은:

👉 “심각하고 고정된 변형”

👉 다장기 이상 동반

Trisomy 21은:

👉 경미한 구조 변화

👉 soft marker 중심

하나의 손가락 소견만으로 판단하지 않습니다.

🔥 핵심 한 줄

T18은 “형태가 무너진 패턴”

T21은 “부드러운 마커의 조합”

초음파는 차이를 읽는 검사입니다.

Classic Limb Findings on Prenatal Ultrasound

Trisomy 18 is a chromosomal condition associated with multiple structural abnormalities.

Limb findings are among the most characteristic and recognizable ultrasound clues.

Recognizing these patterns helps guide further evaluation and counseling.

1️⃣ Clenched Hands with Overlapping Fingers

🔎 Classic Finding

The most well-known limb sign of Trisomy 18 is:

• Persistent clenched hands
• Index finger overlapping the 3rd finger
• 5th finger overlapping the 4th finger

📌 Key Ultrasound Clues

• Fingers remain flexed across multiple scans
• Fixed position
• Limited spontaneous movement

👉 Transient hand flexion is common.

👉 Persistent, fixed overlapping is concerning.

2️⃣ Rocker-Bottom Foot

🔎 Appearance

• Prominent convex sole
• Vertical talus
• Abnormal foot contour

Often associated with severe chromosomal or structural abnormalities.

3️⃣ Overlapping Toes

Different from simple curly toes.

Concerning Features:

• Clear crossing pattern
• Fixed position
• Often bilateral
• Associated with other anomalies

Overlapping toes alone are not diagnostic,

but in combination with other findings → suspicion increases.

4️⃣ Shortened Long Bones

May be present but usually mild.

Important distinction:

• Trisomy 21 → isolated short femur can be common
• Trisomy 18 → shortening often accompanies multiple structural anomalies

5️⃣ Radial Ray Abnormalities (Less Common)

• Absent or hypoplastic radius
• Limited forearm movement

Not universal, but can be seen.

🧠 Pattern Recognition Matters

Trisomy 18 is rarely diagnosed by a single limb finding.

Instead, look for a constellation:

✔ Growth restriction

✔ Cardiac defects (VSD common)

✔ Choroid plexus cyst

✔ Clenched hands

✔ Rocker-bottom feet

✔ Omphalocele

✔ Polyhydramnios

The combination raises suspicion.

🚨 What Makes It Concerning?

Not just the position — but:

• Persistence
• Fixation
• Symmetry
• Association with systemic anomalies

One soft marker ≠ diagnosis.

Pattern = risk.

📌 Clinical Takeaway

Classic limb findings in Trisomy 18 include:

• Persistent clenched hands
• Overlapping fingers
• Rocker-bottom feet
• Overlapping toes

But interpretation must always consider the entire fetal anatomy and growth pattern.

Ultrasound is about patterns, not isolated images.

Related Articles

NIPT vs Ultrasound

Down Syndrome (Trisomy 21)

Understanding the Limits of Early Scans

Many parents feel surprised — or even disappointed —

when a predicted gender later turns out to be incorrect.

They often ask:

“How could this happen?”

“Isn’t ultrasound supposed to be accurate?”

The answer lies in timing, angle, and development.

1️⃣ Too Early in Pregnancy

Before 14 weeks:

• External genitalia are still developing
• Male and female structures look very similar
• The genital tubercle (nub) can change orientation

At this stage, prediction is not confirmation.

Even experienced sonographers can be limited by biology.

2️⃣ Fetal Position Matters

Ultrasound depends on:

• Baby’s position
• Leg placement
• Umbilical cord location
• Imaging angle

For example:

• Umbilical cord between the legs can mimic male anatomy
• Labial folds can be mistaken for scrotum
• A partially hidden penis may not be visible

Angle and movement can mislead interpretation.

3️⃣ Imaging Plane Is Critical

Gender identification requires:

• A clear sagittal or transverse view
• Proper alignment
• Adequate resolution

If the imaging plane is slightly off,

structures may appear different than they truly are.

4️⃣ Developmental Variation

Not all fetuses develop at the same pace.

Some structures:

• Are less prominent early
• Become clearer with gestational age

A structure that looks ambiguous at 13 weeks

may be obvious at 20 weeks.

5️⃣ Technical Factors

Image quality depends on:

• Maternal body habitus
• Machine settings
• Operator experience
• Amniotic fluid amount

These factors affect clarity and confidence.

When Is Gender Most Reliable?

• Before 14 weeks → Higher uncertainty
• 14–16 weeks → Improving reliability
• 18–22 weeks → Most accurate period

Accuracy improves with maturity and better visualization.

Important Perspective

Ultrasound is designed primarily to:

• Assess fetal anatomy
• Evaluate growth and well-being

Gender determination is secondary.

When prediction is wrong,

it usually reflects normal limitations — not error.

Key Takeaways

Accuracy improves after 18 weeks

Early gestational age increases uncertainty

Fetal position can mislead interpretation

Imaging angle matters

Anatomy develops over time