Final answer:
The developing baby is in the fetal period of prenatal development from the ninth week through birth, marked by significant growth and organ development over approximately 30 weeks.
Step-by-step explanation:
From the ninth week through birth, a developing baby is in the fetal period of prenatal development. This stage includes the final stages of growth and differentiation for many of the body's organ systems.
During the fetal period, the organism is called a fetus, and this phase lasts roughly 30 weeks. It is a time marked by significant growth in length and weight of the fetus, and it concludes with a developed newborn capable of survival outside the womb.