| From 7 to 16 days postconception, the yolk sac develops and early development of the primary chorionic villi takes place. |
| Amniotic fluid, chorionic villi, or fetal serum can be tested for evidence of West Nile virus infection. |
| Women at higher risk of carrying a baby with such conditions may opt for testing procedures like amniocentesis or chorionic villus sampling. |
| Another prenatal test, called chorionic villus sampling, can diagnose most, but not all, of the same birth defects as amniocentesis. |
| Prenatal tests called amniocentesis and chorionic villus sampling can diagnose Tay-Sachs before birth. |
| Chorioallantoic or chorionic placentas represent specializations in a chorionic sac surrounding the embryo. |
