What are the three periods of fetal development?

The three periods of fetal development are classified as pre-embryonic, embryonic, and fetal. The pre-embryonic period occurs from fertilization until the end of the second week, where the fertilized egg develops into a blastocyst and implants itself into the uterine lining. This stage is crucial for the initial cellular divisions and preparation for further development.

The embryonic period spans from the third week to the end of the eighth week of gestation. During this time, the basic structures of the body begin to form, including the major organs and systems. This period is characterized by rapid growth and differentiation of tissues, making it a vital time for the development of the embryo.

The fetal period extends from the ninth week of gestation until birth. It is marked by the continued growth and maturation of the already developed organs and systems. This period allows the fetus to gain weight and refine its functional abilities in preparation for life outside the womb.

Understanding these three distinct periods provides insight into the progressive stages of development before birth, highlighting critical phases that influence the health and development of the fetus. The other options reference terms that may not accurately represent the specific stages of developmental biology recognized in obstetrics.