Amniocentesis is done to detect all fetal abnormalities, except?

HPSSC - 2015

Obstetrics & Gynaecology

Medium

Appeared in: HPSSC - 2015

Explanation

Mental retardation is a diagnosis of cognitive and adaptive functioning, which cannot be measured prenatally from amniotic fluid.
It is a clinical diagnosis made after birth based on developmental milestones and standardized intelligence (IQ) testing.
While some genetic conditions identified by amniocentesis (like Down syndrome) are associated with intellectual disability, the test identifies the genetic cause, not the functional outcome of mental retardation.

Option B: Down syndrome is a primary indication for amniocentesis. The procedure allows for karyotyping of fetal cells to confirm the presence of Trisomy 21, the chromosomal abnormality that causes Down syndrome.
Option C: Amniocentesis is a key diagnostic tool for open neural tube defects (ONTDs). Elevated levels of alpha-fetoprotein (AFP) and the presence of acetylcholinesterase (AChE) in the amniotic fluid are highly indicative of an ONTD like spina bifida.
Option D: The Lecithin-sphingomyelin (L/S) ratio is a classic test performed on amniotic fluid to determine fetal lung maturity. A ratio of 2:1 or greater typically indicates that the fetal lungs are mature enough to support breathing outside the womb.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Indications and limitations of amniocentesis as background academic context rather than a clinical decision trigger.
Nurses must provide accurate pre-procedure counseling, explaining that amniocentesis diagnoses specific genetic and biochemical issues but cannot predict functional outcomes like IQ or the presence of mental retardation.
Clarifying the test's limitations is crucial for managing patient expectations and reducing anxiety about the results.
What if? If a patient has a family history of a specific metabolic disorder (e.g., Tay-Sachs disease), amniocentesis can be used to test for that specific enzyme deficiency, which is a known cause of severe neurodegeneration and intellectual disability. In this case, it indirectly predicts a condition that leads to severe mental retardation.

How to Approach the Question

First, identify the keyword "except." This signals that you need to find the one option that is NOT detected or assessed by amniocentesis.
Next, recall the purpose of amniocentesis: it is an invasive procedure to obtain a sample of amniotic fluid for analysis.
Evaluate each option by asking, "Can this condition or value be determined by analyzing fetal cells or chemicals in the amniotic fluid?"
Down syndrome: Yes, by karyotyping fetal cells.
Open neural tube defect: Yes, by measuring alpha-fetoprotein (AFP) levels in the fluid.
Lecithin-sphingomyelin ratio: Yes, it's a direct biochemical measurement of the fluid to assess lung maturity.

Concept Tested & Keywords

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