Hearing that your prenatal screening shows a high risk for a neural tube defect (NTD) can be frightening. Many expectant parents worry that something is wrong with their baby.
Fortunately, a screening test is not a diagnosis. It only estimates the chance of a condition. A detailed fetal ultrasound provides much more information about your baby’s brain and spine.
What Is a Neural Tube Defect?
The neural tube is an early embryonic structure that develops into the baby’s brain and spinal cord. If it does not close completely during early pregnancy, a neural tube defect may occur.
Common neural tube defects include:
- Spina bifida
- Anencephaly
- Encephalocele
Why Was My Screening Test High Risk?
One of the most common reasons is an elevated maternal serum alpha-fetoprotein (AFP) level.
However, AFP can also be higher than expected for reasons unrelated to neural tube defects, such as:
- Incorrect pregnancy dating
- Twin or multiple pregnancy
- Placental conditions
- Individual biological variation
- A completely healthy pregnancy
This is why a high-risk screening result does not automatically mean your baby has a neural tube defect.
What Does the Detailed Ultrasound Evaluate?
1. The Baby’s Spine
The sonographer carefully examines the entire spine from the neck to the lower back.
They look for:
- Proper alignment of the vertebrae
- Intact skin covering the spine
- Any openings or abnormalities
2. The Baby’s Head Shape
Certain brain and skull changes can suggest spina bifida.
During the examination, the sonographer checks for classic ultrasound findings such as:
- Lemon sign
- Banana sign
These are indirect markers that may indicate an underlying spinal defect.
3. The Brain Ventricles
The lateral ventricles are measured carefully because some babies with spina bifida develop enlarged ventricles (ventriculomegaly).
4. The Cerebellum and Posterior Fossa
The cerebellum and surrounding structures are evaluated to identify any changes associated with neural tube defects.
5. Fetal Movement
The baby’s leg movements, foot position, and overall activity are also observed.
Normal movement provides reassuring information about fetal neurological function.
What If the Ultrasound Is Normal?
In many cases, the detailed ultrasound shows no evidence of a neural tube defect.
A normal examination significantly reduces the likelihood of major open neural tube defects. Occasionally, your healthcare provider may recommend a follow-up ultrasound depending on the pregnancy stage or fetal position.
Final Thoughts
A high-risk screening result is not the same as a diagnosis.
Many parents who are referred for a detailed ultrasound receive reassuring news after the examination.
The purpose of the detailed ultrasound is to carefully assess the baby’s brain, spine, and overall development, helping provide the most accurate information possible for you and your healthcare team.
