Definition - What does Embryo mean?

An embryo is a result of a mature egg being fertilized by sperm in the woman’s reproductive system, or in a lab-based environment during assisted reproductive treatments (ART). An embryo is one of the earliest stages of development and comprises the period between the 5th and 8th week of gestation.

During in vitro fertilization (IVF), embryos are created in a lab with collected or donor sperm and eggs, then transferred to a uterus with hopes of implantation and growth.

FertilitySmarts explains Embryo

Sperm and egg typically meet in the fallopian tube. If fertilization occurs, the newly joined unit travels through the remainder of the tube en route to the uterus. During this time in the fallopian tube, the fertilized egg is called a zygote. It contains 46 chromosomes, half from the mother, half from the father, which determine the baby’s sex and characteristics.

While the zygote moves through the fallopian tube it is developing rapidly, dividing and forming new cells, growing together in a small mass. As the cells continue to divide, and the mass continues to grow, it becomes known as a blastocyst.

The blastocyst has two distinct sections, an inner group of cells that will become the fetus, and a second, outer group of cells that will be the placenta and other supportive features. At this stage, the blastocyst implants into the uterine wall, where it will continue to grow while being protected and receiving nourishment from the rich uterine lining. The placenta, formed from the cells in the outer layer of the blastocyst, also begins to grow.

The third week after conception is the beginning of the embryonic period when the mass of cells is officially considered an embryo. It is during this time that the heart, brain, spinal cord, and organs begin to develop.

During in vitro fertilization (IVF), the embryo develops in an identical fashion, except it occurs in a lab-based environment instead of the fallopian tubes. By the time the embryo has begun to develop, it is being prepared for transfer to a uterus.

During the embryonic phase, the presence of genetic issues poses the highest risk to the fetus’ development. If the zygote inherited an abnormal number of chromosomes, the development system may struggle to overcome the complication. As a result, the embryo would be unable to grow properly, which could cause a miscarriage.

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