Physiology of Making Babies

From birth a woman’s ovaries are packed with up to 2 million eggs. Many of these eggs will die off immediately leaving around 400 to be released during a woman’s fertile years. After every period at least one egg will start to mature in your ovaries – some women will mature up to 3 eggs at one time. During ovulation the ripest of these eggs will be released (in some cases more than one egg). The egg is then taken up by one of your two fallopian tubes which are a pathway from your ovaries to your uterus.

When ovulation occurs, which for a 28 day cycle is usually between 12-14 days before your next period, the ripe egg is released. This egg will live around 24 hours and if it is not fertilised by a sperm within this time it will disintegrate. If the egg is fertilised by a sperm then the process of new life begins.

If you are not pregnant the ovary hormone levels reduce in oestrogen and progesterone which signals the thickened lining of the uterus to shed resulting in your period.

Men - Men continuously produce millions of sperm whose sole purpose is to swim towards a woman’s egg and penetrate the wall of the egg. Sperm cells only live several weeks inside a man’s body so the cycle of the sperm being produced and dying off is continuous.

Sperm is produced in the testicles which are on average 4 degrees cooler than the rest of the body in order to keep the sperm healthy. This is why studies into things such as frequent cycling, use of a laptop, tight underwear, hot baths and proved to reduce the number of healthy sperm in men.

Prior to ejaculation sperm is mixed with semen, the sperm will then carry out its one mission in life to find the egg and penetrate the wall. Despite millions of sperm completing during this journey only one sperm can penetrate the egg wall. If the winning sperm contains a Y chromosome then your baby will be a boy and if the sperm has an X chromosome your baby will be a girl.

Sperm can reach the egg as fast as 45 minutes however sperm can survive in a woman’s body for up to 3 days so if the woman’s egg has not yet been released the sperm will hang around and wait for that to happen.