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

• A. Gestational age
• B. Sex of the fetus
• C. Chromosomal defects
• D. Neural tube defects

Answer: (B)

Amniocentesis is done to obtain fetal cells from the amniotic fluid so the fetal karyotype can be analyzed for chromosomal abnormalities. At about 15 weeks, these cells are cultured and examined to diagnose conditions such as trisomies or sex chromosome anomalies. While you can infer fetal sex from the karyotype if needed, the primary use of this test is to detect chromosomal defects. Gestational age is determined mainly by ultrasound dating, not amniocentesis. Neural tube defects are typically screened with ultrasound and maternal serum AFP, with amniotic fluid AFP playing a secondary role only in specific cases. Therefore, the key purpose is identifying chromosomal abnormalities, with sex information being a possible secondary finding.