A client who is 15 weeks pregnant comes to the clinic for amniocentesis. Which of the following is a valid use of this test?

• A. Chromosomal defects
• B. Neural tube defects
• C. Fetal demise
• D. Sex of the fetus

Answer: (B)

Midpregnancy amniocentesis is performed to analyze the fetal components in the amniotic fluid, especially alpha-fetoprotein (AFP) and acetylcholinesterase. When the neural tube doesn’t close properly, AFP leaks into the amniotic fluid and acetylcholinesterase becomes detectable. A combination of elevated AFP and positive acetylcholinesterase in the amniotic fluid is highly indicative of an open neural tube defect, making this a direct, diagnostic use of the test at about 15 weeks. Fetal demise isn’t diagnosed by this test, and while genetic testing on amniotic cells can reveal chromosomal abnormalities, the scenario here specifically points to detecting neural tube defects rather than sex determination or demise.