The embryonic stages between conception and birth include the zygote, morula, blastocyst, embryo and fetus, states the American Pregnancy Association. The stage between conception and growth is the zygote, and upon cell division, it becomes a morula. The morula becomes a blastocyst and attaches to the uterus, and six to 12 days after conception, the blastocyst transitions into an embryo. At 10 weeks, the fetal period begins, and the embryo is now termed a fetus.
The zygote is a fertilized egg, while the morula comes following the first cell division. It becomes a blastocyst once it has separated into two sections, states Mayo Clinic. The inner blastocyst becomes the embryo, with the outer group of cells protecting it. Once the blastocyst reaches the uterus, it attaches to the uterine wall, which is known as implantation.
The third week after conception is the start of the embryonic period. The embryo begins to grow its brain, spinal cord, heart and other organs, notes the American Pregnancy Association. The ninth week of embryonic development marks the beginning of the fetal period, at which point the head is half of the size of the fetus, and the eyelids close to protect the eyes. The fetal period lasts until birth and is marked by continued growth of all bodily systems and increased weight and size of the fetus.