Pregnancy begins with the union of a sperm and an egg. This process, known as fertilization, occurs when a sperm successfully penetrates and fertilizes an egg, typically in the fallopian tubes. The resulting fertilized egg, called a zygote, then travels down the fallopian tube towards the uterus.
Implantation and Beyond
Pregnancy is officially established when this fertilized egg implants itself into the uterine lining. This implantation process typically takes place around 6-12 days after fertilization. Following implantation, the zygote begins to rapidly divide and develop into an embryo, then a fetus.
- Weeks 1-2: While technically the beginning of the process, these weeks don't constitute pregnancy yet.
- Week 5-6: The fetal heart begins to form and pulse. Buds that will eventually become arms and legs also appear.
- Week 8: The embryo is now considered a fetus; the lower limb buds start to shape, and fingers begin to form.
- Beyond 8 weeks: The fetus continues to grow and develop, with organs and body systems maturing throughout the pregnancy. The placenta, a vital organ that provides nutrients and oxygen to the fetus, also forms during this period.
The process is a complex interplay of hormonal changes and cellular development, culminating in the growth and development of a new human life. Note that in some species, like seahorses, pregnancy can involve the male carrying the developing offspring. However, the fundamental principle remains the union of genetic material initiating development.
