Solution:

Within 24 hours after fertilization, the egg begins dividing rapidly into many cells. It remains in the fallopian tube for about three days. The fertilized egg (called a blastocyte) continues to divide as it passes slowly through the fallopian tube to the uterus where its next job is to attach to the endometrium (a process called implantation). Before this happens, the blastocyst breaks out of its protective covering. When the blastocyst establishes contact with the endometrium, an exchange of hormones helps the blastocyst attach. Some women notice spotting (or slight bleeding) for one or two days around the time of implantation. The endometrium becomes thicker and the cervix is sealed by a plug of mucus.

Within three weeks, the blastocyst cells ultimately form a little ball, or an embryo, and the baby’s first nerve cells have already formed. Your developing baby is called an embryo from the moment of conception to the eighth week of pregnancy. After the eighth week and until the moment of birth, your developing baby is called a fetus.