Here’s everything you need to know about how it happens, how to avoid it and what to do if you think you are pregnant.
How does pregnancy happen?
Women can get pregnant any time after their period has started and they have had unprotected sex with a man.
You can also get pregnant if sperm gets onto hands, sex toys or anything else that comes into contact with your vagina.
Sperm can be released at any time during sex, not just when he climaxes or 'comes' and so the ‘pull-out’ method is not an effective way to avoid pregnancy.
How can I avoid getting pregnant?
The only 100% guaranteed way of not getting pregnant is not to have sex with a man.
However, if you are having sex there are many different types of contraceptives which can help to stop pregnancy.
Find out more about the different types of contraception that are available to figure out which might be best for you.
And the only 100% foolproof way to avoid sexually transmitted infections is not to have sex!
What if I have an 'accident' during sex?
Maybe a condom burst, came off, or you got carried away and forgot to use one.
In this case, see your doctor or local chemist straight away. Some supermarkets have pharmacies inside, and there's lots of high street chemists you can go to as well. They may be able to give you emergency contraception that will stop you getting pregnant.
Emergency contraception can work up to 72 hours after you have had sex, but the sooner you get it the more likely it is to work.
They can also arrange tests to make sure you haven't caught a sexually transmitted infection.
What if I’m planning a pregnancy?
If you are in a healthy relationship and you and your partner want to have a baby, it’s important to consider all your options before you have unprotected sex.
I think I'm pregnant - what should I do?
Speak to your school nurse, midwife or doctor.
They can give you a free pregnancy test and will help you work out what to do next.
Pregnancy test kits can also be bought from chemists and most supermarkets. Read the instructions carefully.
If your period is late, it might not be because you're pregnant.
What if the pregnancy test is positive?
It's important you speak with someone about what's going on as soon as possible.
It's your choice whether or not to have the baby, but it's a big decision either way and there's a lot to think about.
Your doctor or school nurse is the best choice or you can visit a sexual health clinic.
They will be able to reassure you and help you decide what to do next.
It's also really important that you're not alone with this. Get extra support from your family or carers if you feel able, or from trusted friends.
If you don't want to speak to people you know just yet, you can call Childline free at any time on 0800 1111.
Remember: in the UK the legal age of consent is 16. This means that according to the law, only those who are aged 16 or over are able to freely agree to any sexual activity.
Find out more about Pregnancy & Parenthood by checking out the PING Campaign