Egg cells mature in the woman’s ovaries. During ovulation the egg is released from the ovaries and moves into the Fallopian tube. The egg then starts to move through the Fallopian tube towards the womb.
If sperm cells from the man reach the womb or the Fallopian tube, one of them can merge with the egg. This is known as conception, or fertilisation, and this is the start of a new human life. Genes from the man and the woman mix so a completely new person is created, someone inheriting characteristics from both the mother and the father.
Once the sperm and egg cells have merged together, the fertilised egg divides into two new, identical cells. The cells continue to divide about once every 24 hours. First there are four, then eight, then sixteen cells. After three weeks the heart starts to beat, and after four weeks the heart is pumping blood to the liver and the main arteries.
The foetus (as the baby is called before it is born) attaches itself to the inside of the womb and gets nutrition through the blood in the umbilical cord, and then continues to grow until it is ready to be born after nine months.