Your baby
One sperm cell, one of many millions, has managed to reach the egg. As soon as it enters the egg's outer layer, that layer changes shape so that no other sperm can get in. Egg and sperm now merge, the way two soap bubbles join.
And without your being aware of any of it, an outright miracle has taken place inside you: you are pregnant. Congratulations. Once egg and sperm have merged they begin dividing immediately and set off for the womb. It is a journey of nothing — a few centimetres — yet the fertilised egg takes several days over it.
Meanwhile the hormones progesterone and oestrogen have already set to work preparing the womb. By the time the egg arrives, the womb is ready for it.
It is hard to believe, but that tiny clump of cells less than 1 mm across, invisible to the naked eye, already determines whether you will have a boy or a girl, what colour eyes your child will have, what colour hair, what build — and even what character.
You
From the moment you are pregnant, a hormone factory starts up in your body. The hormone hCG is produced immediately after implantation, and that in turn indirectly drives the production of other hormones such as oestrogen and progesterone. Progesterone sets to work at once making the mucus in the cervix impenetrable, and it also raises your body temperature slightly — by up to half a degree.
Your temperature stays a little higher throughout your pregnancy. Do you lose a little blood towards the end of this week? That may be an implantation bleed: as the egg settles in, a small blood vessel can be damaged. You may even feel slightly different this week.
Then again, you may notice nothing at all. Or you may put the symptoms down to a period on its way — the two are, after all, very much alike. For an answer to the question of whether you are pregnant, you will have to be patient a little longer.
Only at the end of next week, when your period is due, can you do a pregnancy test. You can simply buy one at the chemist, the pharmacy or online; they are all just as reliable.
Your due date
This third week is really the first week you are actually pregnant — the first two weeks come free, as it were. To work out when your child will be born, take the first day of your last period as your starting point. Add 280 days (40 weeks) to that and you have an approximate due date.
First trimester
