Final answer:
Amniocentesis and chorionic villus sampling are procedures used to collect fetal cells for genetic testing; amniocentesis involves amniotic fluid and is done later in pregnancy, while CVS samples chorionic villi earlier on. The placenta and its villi facilitate the exchange of materials between maternal and fetal blood but also allow potentially harmful substances to pass.
Step-by-step explanation:
The main difference between amniocentesis and chorionic villus sampling (CVS) lies in the timing and method of sampling, as well as the type of cells that are collected. Amniocentesis usually happens later in pregnancy, around the 15th to 20th week. During this procedure, amniotic fluid is extracted from the amnion around the fetus. This fluid contains fetal cells that can be analyzed for genetic conditions. On the other hand, CVS is performed earlier, usually between the 10th and 13th weeks of pregnancy. CVS involves taking a sample of the chorionic villi, which are projections of the chorionic membrane that help form the fetal portion of the placenta. Both procedures provide important genetic information, but they carry different risks and offer results at different stages of pregnancy.
The placenta plays a crucial role in supporting fetal development. It serves as an interface between mother and developing fetus, allowing the exchange of nutrients, waste, and gases, while at the same time keeping the maternal and fetal blood supplies separate. The chorionic villi are essential for this exchange. As they contact the maternal blood, they allow for the exchange of substances without the two blood supplies intermixing. It's important for expectant mothers to avoid fetotoxic substances, since the placenta is permeable to several of them, which can harm the developing fetus and lead to conditions like fetal alcohol spectrum disorders (FASD).