the Role of High-Level Ultrasound and Amniocentesis in Detecting Fetal Abnormalities

Can high-level ultrasound or amniocentesis determine the severity of fetal abnormalities?

I had abnormal alpha-fetoprotein (AFP) levels in my second serum test, so I underwent a high-level ultrasound.
Although the doctor examined for an hour and then discussed the findings with us for another hour, the conclusion was that he did not find any significant issues and did not recommend amniocentesis.
He mentioned that it could be due to other reasons, such as a small part of my placenta being dysfunctional and previous bleeding causing elevated AFP levels.
However, we are aware that the baby's position may have affected the ultrasound results, and the doctor was unable to visualize a small portion of the spine.
This has left us feeling very confused.

What is the purpose of amniocentesis? If the high-level ultrasound can detect neural tube defects (NTDs), why is amniocentesis only recommended when problems are identified? Isn't it the case that amniocentesis is suggested when high-level ultrasound cannot provide clear answers? Additionally, can high-level ultrasound or amniocentesis determine the severity of fetal abnormalities? Does the size of the spinal defect have a greater impact on severity, or is the location of the defect more significant? If there is a very small defect near the upper or cervical spine, would it still be considered severe? I am currently 21 weeks pregnant and will soon be 34 years old.
I would greatly appreciate your response so that I can make an informed decision.
Thank you very much.

Kunhuo de mama, 30~39 year old female. Ask Date: 2010/08/27

Dr. Lü Lizheng reply Obstetrics and Gynecology

There is no need to worry excessively.
Abnormal levels of alpha-fetoprotein (AFP) often result in false positives, and if a high-level ultrasound does not reveal any abnormalities, it is usually considered normal.
If there are still concerns, it is advisable to visit a medical center, such as National Taiwan University Hospital, Veterans General Hospital, Mackay Memorial Hospital, or Chang Gung Memorial Hospital, to consult with an obstetrician who specializes in high-level ultrasounds.
The primary purpose of amniocentesis is to detect chromosomal abnormalities, particularly Down syndrome, which is the most common chromosomal abnormality.
Neural tube defects (NTDs) are distinct from chromosomal abnormalities.
It is possible to have normal chromosomes but still have a neural tube defect, or vice versa—chromosomal abnormalities with a normal neural tube, or both being normal.
If the concern for a neural tube defect arises solely from elevated AFP levels, high-level ultrasound should be prioritized.
An additional benefit of amniocentesis is that it allows for the measurement of fetal protein in the amniotic fluid while conducting chromosomal testing, which is more accurate than measuring fetal protein in the mother's blood.
If the fetal protein in the amniotic fluid is normal, you can feel more reassured.
However, even if the fetal protein in the amniotic fluid is abnormal, further confirmation through high-level ultrasound is necessary.
Of course, high-level ultrasounds may not always detect very subtle abnormalities.
However, if even high-level ultrasounds cannot identify any issues, these subtle abnormalities are usually not significant, and any necessary confirmation or treatment can be addressed after delivery.
I encourage you to consult with an obstetric specialist at a medical center for further examination, which should help clarify your concerns.
Sincerely, Dr.
Lu Li-Cheng, Department of Obstetrics and Gynecology, Taoyuan Hospital.

Reply Date: 2010/08/27

More Info

Understanding the role of high-level ultrasound and amniocentesis in detecting fetal abnormalities is crucial for expectant parents, especially when faced with abnormal serum markers like elevated alpha-fetoprotein (AFP). High-level ultrasound, also known as detailed or targeted ultrasound, is a non-invasive imaging technique that provides a comprehensive assessment of the fetus's anatomy and can identify potential abnormalities, including neural tube defects (NTDs) and other congenital anomalies.

When a serum screening test indicates an abnormal AFP level, it can be concerning. However, it is important to note that elevated AFP levels can sometimes result from factors unrelated to fetal abnormalities, such as maternal conditions or placental issues. In your case, the physician's conclusion after a thorough high-level ultrasound examination—where they did not find significant abnormalities—suggests that the elevated AFP may not be indicative of a serious issue. The mention of a dysfunctional area of the placenta and previous bleeding as possible explanations for the elevated AFP is consistent with clinical understanding.

Amniocentesis is an invasive procedure that involves sampling the amniotic fluid surrounding the fetus. The primary purpose of amniocentesis is to analyze the genetic material of the fetus for chromosomal abnormalities, such as Down syndrome, and to assess the presence of certain conditions. While high-level ultrasound can detect physical anomalies, it does not provide genetic information. Therefore, if there is a suspicion of a chromosomal abnormality based on serum screening or ultrasound findings, amniocentesis may be recommended.

Regarding your confusion about the timing of amniocentesis, it is typically suggested when there are clear indications of potential abnormalities that cannot be confirmed through ultrasound alone. If the high-level ultrasound shows no significant issues, the physician may not recommend amniocentesis, as the risks associated with the procedure (such as miscarriage) may outweigh the benefits. It is also important to understand that high-level ultrasound has limitations; it may not detect very subtle abnormalities, and some conditions may only be confirmed through genetic testing.

As for the severity of abnormalities, particularly concerning neural tube defects, both the size and location of the defect can influence the prognosis. For example, a larger defect may be associated with more significant neurological impairment, while the location—whether it is in the lower or upper spine—can also affect the severity of associated complications. A small defect located near the upper spine or neck may still have serious implications, depending on the structures involved and the extent of the defect.

In your case, given that you are currently 21 weeks pregnant and approaching the age of 34, it is understandable to feel anxious about the potential outcomes. It is essential to maintain open communication with your healthcare provider, who can guide you through the decision-making process based on the most current information and your specific circumstances. If you still have concerns or uncertainties, seeking a second opinion from a maternal-fetal medicine specialist at a tertiary care center may provide additional reassurance and clarity.

Ultimately, the decision to proceed with amniocentesis or to rely on high-level ultrasound findings should be made collaboratively with your healthcare provider, considering both the potential risks and the information you hope to gain. It is crucial to weigh the benefits of obtaining more definitive answers against the risks associated with invasive procedures. Your peace of mind and the health of your baby are of utmost importance, and your healthcare team is there to support you through this journey.

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