Your guide to the second week of pregnancy
Oestrogen also thins the mucus in your cervix (the entrance to your womb), to allow your partner’s sperm to swim through into your womb and up the fallopian tubes to meet your egg. Sperm is usually prevented from doing this by the thickness of the cervical mucus which creates a barrier.
One of your eggs will be growing faster than the rest and at the end of this week it will become too big for its sac. Your body will produce a surge of luteinising hormone (LH) which triggers the sac to split and release your egg into your fallopian tube, where it moves slowly towards your womb.
En route it will be met and fertilised by just one sperm. There are a staggering 300 million sperm in the race to your egg. That’s how much your partner produces when he ejaculates. But most never make it off the starting blocks! Around 300 will reach your egg but only one manages to wriggle through and fertilise it.
Experts don’t fully understand what singles out the successful sperm. But scientists at Bath University recently identified hundreds of proteins which make up each sperm, and they believe these proteins hold the key to how sperm manages to swim so far and sabotage the efforts of rival sperm in the race to the egg.