Final answer:
During the first trimester, limb buds form and the heart develops. In the second trimester, the fetus grows to 30 cm and begins moving. The third trimester is marked by rapid growth and increased body fat.
Step-by-step explanation:
During the first trimester, the period brackets the laying down of the fundamental structures of the body, such as limb buds, heart formation, and the development of eyes and the liver. In the second trimester, the fetus experiences significant growth, reaching about 30 cm (12 inches). The mother begins to feel fetal movements, and all organs and structures continue their development, including the fetal activation of the thyroid, liver, pancreas, and kidneys. Notably, the placenta takes over roles in nutrition and waste management as well as hormone production. The third trimester is characterized by rapid fetal growth, increases in body fat, further skeletal development, and the darkening of head hair. The protective lanugo is shed, and the eyes develop to detect light.
Two important developments for each trimester are:
-
- First trimester: Formation of limb buds and the heart.
-
- Second trimester: The fetus grows to about 30 cm and begins moving.
-
- Third trimester: Rapid body growth and increased body fat.