Question

Amniocentesis to detect chromosomal abnormalities can be done as early as

• A. 14th week of gestation
• B. 18th week of gestation
• C. 22nd week of gestation
• D. 26th week of gestation

Hint:

Amniocentesis needs enough fluid and cells, available from around 14 weeks.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the earliest gestational week at which amniocentesis can be done to look for chromosomal abnormalities in the fetus.

Step 2: Key Formula or Approach:
Amniocentesis needs enough amniotic fluid volume and a good number of viable fetal cells shed into that fluid, so it becomes technically possible only once the second trimester begins.

Step 3: Detailed Explanation:
By around 14 weeks of gestation, there is enough amniotic fluid and enough fetal cells in it to safely withdraw a sample and culture the cells for chromosome analysis.
Most routine genetic amniocentesis is actually performed between 15 and 20 weeks, commonly around 16 weeks, for the best balance of safety and reliable results, but the procedure can technically be attempted from 14 weeks onward.
Options (B) 18 weeks, (C) 22 weeks and (D) 26 weeks are all later than the earliest possible point, so they do not answer "as early as".

Step 4: Final Answer:
Amniocentesis for chromosomal analysis can be done as early as the 14th week of gestation.
\[ \boxed{14^{th} \text{ week of gestation}} \]