Patient Education · Maternal-Fetal Medicine

Understanding Your
Baby's Ultrasound Findings

Your 18-week scan showed several findings. This guide explains what was seen, what it may mean, and exactly what comes next — together with your care team.

Brain findings
Abdominal wall finding
Clear next steps
What Was Found

Four findings were identified on ultrasound

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Ventriculomegaly
The fluid-filled spaces inside the brain (ventricles) appear larger than usual.
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Dilated Third Ventricle
A specific chamber deeper in the brain (third ventricle) is wider than expected.
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Absent Cavum Septum Pellucidum
A small midline brain structure (CSP) that normally appears between 18–37 weeks was not visible.
🩺
Abdominal Wall Defect
A gap in the baby's belly wall where abdominal organs may protrude (possibly omphalocele).
Brain Anatomy

What do these brain structures normally do?

CSP 3V Lateral Ventricles Corpus Callosum 3rd Ventricle Aqueduct
Lateral Ventricles Fluid-filled chambers that cushion and nourish the brain. Normally <10 mm wide at 18 weeks.
Cavum Septum Pellucidum (CSP) A small midline space between two brain membranes. Its presence confirms normal midline brain development.
Third Ventricle A deeper chamber between the two halves of the brain. Dilation may signal a blockage of the passageway below it.
Cerebral Aqueduct The narrow channel that drains fluid downward. Blockage here explains dilation above it.
Why It Matters

The absent CSP is a screening marker — not a diagnosis

Its absence prompts a deeper look. Three conditions are being considered:

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Holoprosencephaly
The brain's two halves didn't fully separate. May range from mild to severe. Often associated with facial and body midline differences.
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Absent Corpus Callosum
The bridge connecting the brain's two halves is missing or incomplete. The third ventricle may be elevated and enlarged.
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Septo-Optic Dysplasia
The CSP and optic nerves did not develop fully. Can affect vision and hormones after birth.
Additional imaging and testing will help distinguish between these possibilities. No diagnosis has been made yet.
Abdominal Wall Finding

Two types of abdominal wall defects — very different implications

Feature Omphalocele Gastroschisis
Location Midline — at the belly button To the right of the belly button
Covering membrane ✅ Organs are covered (protective sac) ❌ Organs are exposed in fluid
Associated chromosomal conditions Up to 50% Rare (<1%)
Co-occurrence with brain findings Common (especially Trisomy 13 & 18) Very uncommon
Most likely finding in your baby ✅ Based on midline location and other findings Less likely
Genetic Risk

When brain + body findings appear together,
chromosomal evaluation is essential

🧬
Trisomy 13 (Patau Syndrome)
An extra copy of chromosome 13. Frequently associated with:

• Holoprosencephaly
• Omphalocele
• Midline structural differences
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Trisomy 18 (Edwards Syndrome)
An extra copy of chromosome 18. May present with:

• Brain structural changes
• Abdominal wall defects
• Multiple organ differences
🔎
Chromosomal Microarray (CMA)
A detailed genetic test that finds changes too small for standard chromosomal testing. Done via amniocentesis. Provides the most complete picture.
Brain Fluid Scale

Ventriculomegaly is graded by measurement in millimeters

Your care team will determine the exact measurement. This scale shows what each level generally means.

Normal Below 10 mm
Mild ventriculomegaly 10 – 12 mm
Moderate ventriculomegaly 13 – 15 mm
Severe ventriculomegaly 16 mm or more
Severity of ventriculomegaly — combined with the underlying cause — guides the overall prognosis. Fetal MRI gives the clearest measurement.
What Happens Next

A step-by-step care plan is already underway

Step 1
Genetic Counseling
Meet with a specialist to review your family history and understand testing options before any decisions.
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Step 2
Amniocentesis
A small sample of amniotic fluid is taken to test the baby's chromosomes. CMA + standard karyotype.
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Step 3
Fetal MRI
Detailed brain imaging that goes beyond ultrasound to define the brain structure more precisely.
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Step 4
Detailed Ultrasound
A targeted neurosonogram to clarify brain anatomy and confirm the type of abdominal finding.
Each test adds a piece to the picture. You will not be asked to make decisions before you have answers.
Understanding the Tests

What each test looks for

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Chromosomal Microarray (CMA)
Examines all 46 chromosomes for extra, missing, or rearranged genetic material — including changes too small for standard testing. Most complete chromosomal analysis available.
📊
Standard Karyotype
Counts chromosomes and checks for large-scale rearrangements like balanced translocations. Together with CMA, provides the fullest genetic picture.
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Fetal MRI
Uses magnetic fields (no radiation). Offers superior detail for brain structure, cortical development, and posterior fossa — especially when ultrasound is limited by fetal position.
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Targeted Neurosonogram
A specialized, extended ultrasound of the brain performed by a maternal-fetal medicine specialist. Evaluates frontal horn shape, optic chiasm, and midline anatomy in greater detail.
Looking Ahead

Prognosis depends on three key factors

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Severity of ventriculomegaly
Mild cases often have very favorable neurodevelopmental outcomes. Severe cases carry greater risk.
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Underlying cause
Chromosomal conditions, structural syndromes, and isolated findings each have different implications.
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Number of findings
Multiple anomalies together increase the likelihood of a syndrome and affect planning for delivery and care.
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Specialist involvement
Early coordination with neonatology, pediatric surgery, and genetics improves preparation and outcomes.
Many families navigate complex prenatal diagnoses and find strength they didn't know they had — with the right team by their side.
Your Role as a Partner

You are an active partner in this process

❓
Ask questions
There is no such thing as a question that is too small. Write them down before each appointment. Bring a support person with you.
📋
Understand your options
Testing is a choice. Your team will explain the benefits and limitations of each test clearly before you decide.
🤝
Lean on support
Social work, genetics counselors, and support groups are available. You do not have to process this alone.
📅 Attend all follow-up appointments
📝 Keep a list of your questions
💬 Share concerns with your care team
🧘 Care for your own wellbeing too
🫶

You have a team.
You are not alone.

This is a complex situation — and it is also one where modern medicine, genetics, and compassionate care can offer meaningful answers. Every step forward brings more clarity.

🧬 Genetic Counselor
🏥 Maternal-Fetal Medicine Specialist
👶 Neonatologist
💼 Social Worker
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Key Reminder
No decisions are required today. Information comes first.