Human Growth and Development

Prenatal Development-Embryonic Period

Significant Changes in the First Two Weeks of Prenatal Development

Several significant changes occur during the first two weeks of prenatal development, as shown in the accompanying table.

Time Period Developmental Stage
12–24 hours following ovulation Fertilized ovum
30 hours to third day Cleavage
Third to fourth day Morula (solid ball of cells is formed)
Fifth day through second week Blastocyst
End of second week Gastrula (germ layers form)