During Week 4 of pregnancy, the single cell zygote divides many times to form a ball of cells, with an inner group and an outer shell, known as a blastocyst. The blastocyst reaches the uterus and within a couple of days, implants itself in the wall.
Did you know?
The uterus consists of a body and a cervix (neck), which has opposing functions during pregnancy. During pregnancy the body of the uterus must remain relaxed and stretch in order to accommodate the foetus and placenta, while the cervix must remain firm in order to maintain the pregnancy. In labour the body of the uterus must contract and retract while the cervix must relax, stretch and open to allow the baby to pass through.