First Trimester Scan Guidelines (11-14 Weeks Anomaly Scan)

1. Grasping the Significance of the First Trimester Scan.
2. Screening for Chromosomal Abnormalities – Decoding Genetics.
3. Identifying Structural Anomalies – Catching Major Issues Early.
4. Twin Pregnancies – Double Joy, Double Risk
5. Placental Concerns – Stay Alert for These.
6. Predicting Preterm Labor – A Work in Progress.
Mon Sep 1, 2025

First Trimester Scan Guidelines (11-14 Weeks Anomaly Scan)

1. Grasping the Significance of the First Trimester Scan
Why is this scan essential?
Think of it as the preview of your pregnancy journey—it offers an early glimpse into potential issues, enabling you to address con
✅ Early identification leads to improved outcomes
✅ Detects chromosomal abnormalities, structural issues, and maternal health risks
✅ Enhances management of pregnancy before they escalate into major problems.
2. Screening for Chromosomal Abnormalities
Decoding Genetics.Aneuploidy refers to an irregular number of chromosomes, much like ordering a pizza and receiving either too many or too few slices.
Key Aneuploidies to Keep in Mind.

Aneuploidy	Important Features	Outlook
Trisomy 21 (Down Syndrome)	Elevated NT, absent nasal bone, heart defects	Can survive into adulthood with cognitive challenges
Trisomy 18 (Edwards Syndrome)	Growth restriction, clenched fists, omphalocele	Severe, typically fatal in infancy
Trisomy 13 (Patau Syndrome)	Holoprosencephaly, midline facial deformities, extra digits	Severe, often leads to fatality
Monosomy X (Turner Syndrome)	Cystic hygroma, hydrops, aorta coarctation	Survival hinges on severity

Main Idea:
The NT measurement (Nuchal Translucency) is the cornerstone of first-trimester evaluations.
For enhanced accuracy, combine NT, nasal bone visibility, ductus venosus flow, tricuspid regurgitation, and serum markers (β-hCG & PAPP-A)!

How to Conduct Aneuploidy Screening?

Screening Approach	Metrics Assessed	Detection Rate
NT Scan + Biochemistry	NT, nasal bone, β-hCG, PAPP-A	85-90%
NIPT (Non-Invasive Prenatal Testing)	Cell-free fetal DNA	>99% for Trisomy 21
CVS/Amniocentesis	Direct genetic analysis	100% but invasive

Key Takeaway:
✔ NT > 3.5mm? → High risk! Further investigation needed!
✔ Isolated thick NT doesn’t equal Down Syndrome → Could indicate heart or skeletal issues too!
✔ NIPT is effective but not reliable for twins!
3. Identifying Structural Anomalies – Catching Major Issues Early.
(The first trimester is crucial for detecting potential problems.
1. Neural Tube Defects (NTDs) – Checking the Brain & Spine.

Condition	First Trimester Indicators	Implications
Anencephaly	Missing skull bones, frog-like face appearance	Fatal
Spina Bifida	Lack of intracranial translucency	Open defect requiring surgery
Iniencephaly	Severe neck hyperextension	Fatal

Simple Tip:
NTDs = Focus on Brain & Spine!
If Intracranial Translucency is absent → Spina Bifida Alert!
2. Abdominal Wall Defects – Issues with Baby’s Abdomen

Condition

Ultrasound Findings

Key Distinction

Omphalocele

Bowel covered by membrane, central defect

Linked to aneuploidy

Gastroschisis

Bowel floating freely in amniotic fluid

Isolated, generally better outlook

3. Congenital Heart Defects – The Heart Detective’s Task! ❤️

(Early heart problems can be like an ex—spotting warning signs is crucial! 🚩😆)

Top Screening Techniques in the First Trimester:

✔ 4-chamber view (Ensures all heart chambers are present!)

✔ Three-vessel tracheal view (3VT) (Alignment of major vessels)

✔ Ductus Venosus Flow (Abnormal A-wave? Possible CHD!)

Defect	Ultrasound Clue	First Trimester Indicator
Tetralogy of Fallot (TOF)	Overriding aorta, reduced pulmonary artery size	Elevated NT, abnormal DV flow
Hypoplastic Left Heart Syndrome (HLHS)	Small left ventricle size	Single AV stripe present
AVSD (Atrioventricular Septal Defect)	Common AV valve with large septal defect	Strongly associated with Down Syndrome

💡 Golden Rule: Cardiac issues are more frequent in babies with high NT!

4. Twin Pregnancies – Double Joy, Double Risk! 👶👶

(Twins can mean double trouble, especially when sharing a placenta! 😅)

Understanding Chronicity (Not all twins are created equal!)

Twin Category

Ultrasound Significance

Risk Level

Dichorionic Diamniotic (DCDA)

Lambda (Twin Peak) Sign

Lower risk factor

Monochorionic Diamniotic (MCDA)

T-sign indication

Higher risk of TTTS (Twin-to-Twin Transfusion Syndrome)

Monochorionic Monoamniotic (MCMA)

Absence of membrane

Highest risk due to cord entanglement

💡 Note: Monochorionic twins face increased risk of TTTS!

2. Recognizing Twin-to-Twin Transfusion Syndrome (TTTS) – Key Signs to Monitor?

✔ NT Discordance > 20%

✔ Differences in amniotic sac sizes

✔ Abnormal ductus venosus flow

5. Placental Concerns – Stay Alert for These!

(A problematic placenta can hinder your pregnancy journey! 🚧)

1. Vasa Previa – The Quiet Threat! 🚨

Velamentous cord insertion → Cord vessels cross the cervix

High risk of fetal loss if not detected before labor

Identify early with a Transvaginal Scan (TVS)!

2. Placenta Accreta Spectrum (PAS) – The Sticky Placenta Dilemma!

✔ Previous C-section + Anterior placenta = Elevated risk!

✔ Signs to observe:

Placental lakes (Swiss cheese pattern 🧀)

Thinning myometrium

Loss of bladder wall interface

💡 Why It Matters?

PAS poses a significant hemorrhage risk during delivery!

6. Predicting Preterm Labor – A Work in Progress!

(Is it possible to forecast early labor at 12 weeks? Not quite… yet! 😅)

✔ A shortened cervix is linked to preterm birth

✔ Measuring cervical length in the first trimester is not reliably accurate

✔ Ongoing research aims to integrate biochemical markers and patient.

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First Trimester Scan Guidelines (11-14 Weeks Anomaly Scan)

First Trimester Scan Guidelines (11-14 Weeks Anomaly Scan)

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