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Day 1
Fertilization of zygote and beginning of secretory phase. The fusion of haploid gametes, egg and sperm, to form the diploid zygote starts to take place. Uterine tissue regrowth is completed and preparation for pregnancy and implantation. -
Day 4
The blastocyst has reached the uterine body still enclosed in the zone pellucida and "hatches" from this surrounding extracellular matrix. It is only after hatching that the blastocyst can attach to the uterine wall and implant. -
Day 7/8
Attachment and invasion of the uterus endometrium by the blastocyst. The first phase requires the newly hatched blastocyst to loosely adhere to the endometrial epithelium "rolling" to the eventual site of implantation where it is firmly attached. This process requires both the blastocyst adhesion interaction with the endometrium. development of the placenta allows maternal support of embryonic and fetal development. -
Day 16
Gastrulation starts to form the embryo. The epiblast layer makes all 3 embryo layers: ectoderm, mesoderm and endoderm. The primitive streak is the visible feature which represents the site of cell migration to form the additional layers. -
Day 28
At the ectoderm, the neural tube continues to close, the caudal neuropore closes, and the forebrain starts to form. In the mesoderm, there is continued segmentation of paraxial mesoderm (21 - 29 somite pairs), and more of a heart prominence. -
Day 37
Ectoderm: sensory placodes, lens pit, otocyst,nasal pits moved ventrally, fourth ventricle of brain
Mesoderm: heart prominence
Eye showing retinal pigment, nasolacrimal groove, nasal pit, fourth ventricle of brain, umbilical cord, 1st and 2nd pharyngeal arches, cervical sinus, heart, developing arm with hand plate, foot plate. -
Day 56
This is the final Carnegie stage of embryonic development in Week 8. After this development is considered fetal for the remainder of the pregnancy. Mesoderm: ossification continues
Head: eyelids, external ears, rounded head
Body: straightening of trunk, intestines herniated at umbilicus
Limbs: hands and feet turned inward.
