During this period, the structure of the fetus is completed to the extent that major abnormalities--or good health-- can be determined.
Weeks 15-16: Amniocentesis can be performed to check for birth defects
Weeks 16-18: Substantial cardiac defects can be determined. The fetus is fully formed, about 5 inches long. Fetal heart beats twice as fast as mother's.
Weeks 18-20: Stem cells begin to occupy the fetal bone marrow. Fetus begins to move. Has hair on its head, and teeth are beginning to form.
Weeks 24-28: The fetus tries out leg and arm muscles, kicking, punching, etc. It's 10 inches long and weighs about 2 pounds and can cough, hiccup and respond to sudden noises
SECOND TRIMESTER GLOSSARY:
Amniocentesis: A procedure in which a small amount of amniotic fluid is removed from the uterus by needle. The fluid is tested for chromosomal or genetic abnormalities in the fetus.
Stem cells: The youngest cells in the body, some of which evolve into red blood cells and others into white blood cells.
Bone marrow: Soft material found inside bone cavities that is the site of the formation of blood cells. Sources: Reproductive Health, American Heart Assn., March of Dimes, Anatomy and Physiology the Easy Way. Researched by THOMAS H. MAUGH II/Los Angeles Times
Drawings not actual size