Fusion of ova (egg female gamete)and sperm (male gamete) is called fertilisation.Fertilisation results in the formation of zygote which begins to develop into an embryo.Implantation is the early stage of pregnancy.The cells begin to form groups that develop into different tissues and organs of body.This developed structure is termed as an embryo.The embryo gets embedded in the wall of uterus for further development. The embryo continues to develop in the uterus.It gradually develops the body parts.The stage of embryo in which all the parts of body can be identified is called a foetus.When the development of foetus is complete then the mother gives birth to a baby.That's all.The process of fertilisation to foetus and the changes.