The fertilised egg immediately begins to divide into a growing cluster of cells. Between five and seven days after ovulation, it starts to implant into the wall of the womb. It produces root-like outgrowths that help to attach it to the lining of the uterus. These cells will eventually grow into the placenta, the tube-like organ that connects mother to baby, and feeds and protects the baby until birth.
Around week 3, when the cluster of cells is attaching to the lining of your womb, you might experience pains a bit like period pains. You might have some slight bleeding too, called implantation bleeding. Some women say they know immediately when they become pregnant. You can do a urine pregnancy test but it's not completely accurate at this stage. In some cases, a blood test at your GP's surgery may be used to detect pregnancy 6-8 days after conception. You can alternatively get a test at your family planning or GUM clinic.
If you think you might be pregnant, or are planning to get pregnant, check with your GP or pharmacist about any medicines you're taking, including herbal supplements. As a general rule, it's best to avoid any non-essential medicines while you're pregnant, but you shouldn't stop taking prescribed drugs like antidepressants suddenly - always discuss them with your doctor first. Unfortunately as many as 1 in 4 pregnancies end in miscarriage, and it is particularly likely in first pregnancies. Support and advice is available from your GP and local family planning clinic.