Pregnancy Week 1-4
Week 2
The sperm is approaching the ovum.
Fertilization, the joining of the sperm and the egg in the fallopian tube to form a unique human being, occurs. Forty-six chromosomes provide the blueprint for the embryo’s physical characteristic
fertilized egg.
The developing embryo, called a zygote at this stage, floats down from the fallopian tube and towards the uterus.
Week 3
At this point, the blastocyst, or developing embryo, is looking for a spot to implant in the uterus. Early formation of the central nervous system, backbone, and spinal column has begun. The gastrointestinal system has also begun to develop with the kidneys, liver, and intestines forming. The heart has begun to form.
Week 4
The Embryo at 4 weeks 
Hormones produced by the embryo stop the mother’s menstrual cycle.
The fertilized egg is undergoing rapid cell division. It will implant in your uterine lining this week. Once implantation occurs, it’s called a blastocyst and is very tiny. It only measures 0.1-0.2 mm in diameter.
A yolk sak has developed and will be the nourishment for baby until the placenta is formed and takes over. The sex and other characteristics of your baby have already been decided! It’s all in the DNA code that was formed when the sperm and egg first met.
