Fetus Growth Stages

The journey from individual cell to an individual is a fascinating one. A normal pregnancy lasts for 39 to 40 weeks. The stages of development are fertilized egg, blastocyst, embryo and finally a fetus.

Fertilized Egg

During ovulation, the sperm enters the uterus and implants itself into the egg. Fertilization occurs when the sperm penetrates the egg.

Blastocyst

The fertilized egg develops into a ball of cells, or blastocyst. This development begins five to eight days after fertilization. During this time, the blastocyst attaches itself to the lining of the uterus.

Embryo

The blastocyst continues to develop into an embryo. By week three, internal organs begin to form. During this time, the brain and spinal cord, heart and major blood vessels develop.

Fetus

By week 10 of the pregnancy, the embryo is now considered a fetus. By week 12, the fetus fills the uterine cavity and the sex can now be determined. Fetal movement can be felt anywhere from 16 to 20 weeks.

Viability

By 23 to 24 weeks, the fetus is considered viable, or able to survive outside the womb. The lungs and other major organs are not yet fully mature at this point, and complications are common when a fetus is born so far in advance of the full gestational period of 40 weeks.

References

• PregnancyPeriod: Stage of Pregnancy Development
• BehindtheMedicalHeadlines: Insights Into Early Fetal Development
• PregnancyHealthGuru: First Trimester Pregnancy Stages

Resources

• DocShop: Week by Week Pregnancy Guide
• WhattoExpect: Week by Week Pregnancy Calendar