Which fluid surrounds the fetus and is collected during pregnancy for testing?

Amniotic fluid is the correct choice as it is the fluid that surrounds the fetus during pregnancy. This fluid serves multiple essential functions, including providing a cushioning environment for the developing fetus, allowing for fetal movement, and aiding in the development of the lungs and digestive system. Medical professionals might collect amniotic fluid through a procedure called amniocentesis, which is often performed to conduct tests that can detect genetic conditions, infections, and other issues related to the health of the fetus.

The other options do have specific roles in the body but are not relevant to the context of pregnancy. Serous fluid acts as a lubricant in body cavities, aqueous humor is the fluid in the eye that maintains intraocular pressure, and synovial fluid is present in joints to reduce friction. None of these fluids are involved in the protective environment of the fetus, making amniotic fluid the only appropriate option for this question.