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Preimplantation Period: Week 1
At the beginning of week 1, a woman's ovum is penetrated by a man's sperm during fertilization.
After the fertilization the now zygote undergoes meiosis then mitosis, also known as cleavage. -
Embryonic Period: Week 2
During week 2 of prenatal development, the implanted blastocyst grows due to increased proliferation and differentiation. This then results in alterations in the cellular morphogenesis: ridges, bumps, and recesses are prime indicators of increased levels of cellular differentiation. -
Embryonic Period: Week 3
In the beginning of week 3 in prenatal development, the primitive streak, or a furrowed rod-shaped thickening, forms within the bilaminar disc. The primitive streak is due to the increased proliferation of the cells in midline area. This results in the disc having bilaminar symmetry on either side. -
Embryonic Period: Week 4
In week 4 in prenatal development, the disc undergoes embryonic folding. This then allows for forming tissues to get into their proper positions for further embryonic development. During this week the face and neck begin to develop with the primitive eyes, ears, nose, oral cavity, and jaw. -
Embryonic Period: Weeks 5-8
In week 5 of the prenatal development, the brain, spinal cord, heart, and other organs begin to form. The umbilical cord replaces the yolk sac, and the upper lip is formed when the maxillary process fuses together as well as the nasal process and the rest of the face. -
Fetal Period: Weeks 17-20
In weeks 17-20 of the prenatal development, the soft hair called lanugo starts to form and cover the body. This hair is essential and protects the fetus's skin and keeps them warm in the womb. -
Fetal Period: Weeks 25-28
In weeks 25-28 of prenatal development, the lungs begin to make surfactant which will be needed for breathing after birth. -
Fetal Period: Weeks 33-36
In weeks 33-36 of prenatal development, the fetus's bones have hardened but the skull stays soft and flexible for birth.
Fingernails have grown fully, and fetus may turn into a head-down position for birth. -
Fetal Period: Weeks 37-40
In weeks 37-40 in the prenatal development, all systems are fully developed, and fat is continuously added to fetus to keep it warm after birth. Fetus is ready to be born!