Which of these procedures has the least risk for an unborn child?

The correct option is Alpha-fetoprotein sampling.

To understand why this procedure has the least risk for an unborn child, we can evaluate and compare the nature of each option:

1. Alpha-fetoprotein (AFP) sampling:
This is a simple maternal blood test (usually performed as part of a triple or quad screen). It involves drawing blood from the pregnant mother's arm to measure the levels of alpha-fetoprotein, which is produced by the fetus. Because it is non-invasive and does not involve entering the uterine cavity or touching the fetus/placenta, it poses zero physical risk of miscarriage or injury to the unborn child.

2. Amniocentesis:
This is an invasive procedure where a needle is inserted through the mother's abdomen and uterus into the amniotic sac to retrieve a sample of amniotic fluid. Because it is invasive, it carries a small but real risk of miscarriage, infection, or direct needle injury to the fetus.

3. Chorionic Villi Sampling (CVS):
This is another invasive prenatal test where a sample of placental tissue (chorionic villi) is removed either transcervically or transabdominally. CVS is performed earlier in pregnancy than amniocentesis and carries a slightly higher risk of miscarriage and a potential risk of limb abnormalities if performed too early.

In conclusion, because Alpha-fetoprotein sampling is a routine maternal blood draw, it is entirely non-invasive for the fetus and carries the least risk (effectively no risk) compared to the invasive alternatives.