Which one of the following diagnostic test is used to detect Neural tube defects?

NVS Staff Nurse - 2022

Obstetrics and Midwifery Nursing

Easy

Appeared in: NVS Staff Nurse - 2022

Explanation

Maternal Serum Alpha-Fetoprotein (MSAFP) is a key biochemical marker used as a screening test for neural tube defects (NTDs).
The test measures the level of alpha-fetoprotein (AFP), a protein produced by the fetal liver, which has leaked into the maternal bloodstream.
In pregnancies with an open NTD (e.g., spina bifida, anencephaly), the fetus's AFP leaks into the amniotic fluid and then enters the mother's circulation, leading to elevated MSAFP levels.
It is a non-invasive blood test typically performed between 15 and 20 weeks of gestation.
While not diagnostic, an elevated MSAFP result is the primary indicator that triggers further, more definitive diagnostic testing like ultrasonography.

Option B: Ultrasonography (USG) is a diagnostic tool, not the initial screening test for the general population. It is typically used to confirm a suspected NTD after an abnormal MSAFP screening result by providing a direct visual of the fetal anatomy.
Option C: The Contraction Stress Test (CST) is used to evaluate fetal well-being by monitoring the fetal heart rate's response to uterine contractions. It assesses uteroplacental function, typically in the third trimester, and has no role in detecting structural birth defects like NTDs.
Option D: Percutaneous Umbilical Cord Blood Sampling (PUBS), or cordocentesis, is an invasive procedure to obtain a fetal blood sample from the umbilical cord. It is used for rapid karyotyping, or to diagnose fetal anemia, infections, or certain genetic disorders.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Prenatal screening for neural tube defects as background academic context rather than a clinical decision trigger.
Early screening for NTDs with MSAFP is a crucial part of antenatal care. It allows for timely counseling, further diagnostic workup, and preparation for the birth of a child with special needs, including planning for delivery at a tertiary care center.
A positive screening test can cause significant parental anxiety. Nurses play a vital role in explaining that it is a screening test, not a diagnosis, and providing support while arranging for follow-up diagnostic tests.
What if? If a patient has a twin pregnancy, the interpretation of MSAFP levels is different. AFP levels are naturally higher in multiple gestations, so specific reference values for twins must be used to avoid a high false-positive rate.

How to Approach the Question

First, identify the key concept in the question: the detection of Neural Tube Defects (NTDs).
Next, analyze the options provided and categorize them based on their purpose in prenatal care (e.g., screening, diagnosis, fetal well-being).
Recall that MSAFP is a specific biochemical screening test for NTDs performed on maternal blood.
Recognize that Ultrasonography (USG) is a diagnostic imaging tool, often used to confirm findings from a screening test.
Eliminate Contraction Stress Test (CST) and Percutaneous Umbilical Cord Blood Sampling (PUBS) as they are used for different purposes (fetal well-being and fetal blood analysis, respectively) and are not primary methods for detecting NTDs.
Conclude that MSAFP is the most appropriate answer as it is the standard initial screening test used to 'detect' the risk of NTDs in the pregnant population.

Concept Tested & Keywords

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E6 Anatomy Applied Ashalatha 4e p. 473-475

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