How can you tell if you're expecting a boy or a girl?  The shape of your bump, or dangling a wedding ring over your tummy are just two of the many old wives tales around predicting a baby's sex. 

But although they are fun to try none are proven to be accurate, and the best chance for most women is at the anomaly scan at 20 weeks pregnant.

So how is it done?

Ultrasound scans are usually carried out at certain points of your pregnancy to check your baby’s development. The second routine scan is generally done at around 18-22 weeks, and if you do want to know the sex of your baby it can usually be determined during this scan.

It is important to remember though that the sonographer (the person that does the scan) can never be 100% sure. Sometimes it may not be possible to tell at all, if your baby is facing the wrong way, or is in a position where the sonographer cannot get a good enough view.

It is best to tell the sonographer you would like to find out the gender at the beginning of the scan, so that they know they need to check. In the same way, it is also advisable to let them know from the start if you don’t want to be told so they don’t give it away!

You can also find out baby’s gender through Amniocentesis or Chorionic Villus Sampling (CVS) but these are not used specifically to determine the sex of the baby. You won’t usually be offered these tests unless you are at a higher risk of carrying certain genetic abnormalities.

Why might you want to know?

Some people think that knowing the gender will help them to feel better prepared for baby’s arrival. It can help you to narrow down your choice of names, for example, or help you decide how to decorate the baby’s room. You might want to pick out clothes more suitable for a boy or a girl beforehand.

Some feel it can help them to bond with their baby and ‘get to know’ it before it is born. Those that have a strong preference either way sometimes feel that finding out will help them to prepare themselves emotionally, and get used to the idea if their baby is not the gender they had hoped for.

Others like to keep it as a complete surprise until the birth. Many parents feel that not knowing adds to the excitement and gives them something extra to look forward to. It can also be upsetting, not to mention inconvenient, to be told the sex during pregnancy, only to find out later that it was wrong!

Why won’t some hospitals tell you?

Some hospitals have a policy of not telling parents their baby’s gender. Sometimes this is to avoid disappointment as there is no guarantee that the results will always be accurate.

There can also be concerns that in some cases telling parents may lead to unnecessary terminations of pregnancy if parents have a very strong preference. This could even lead to an imbalance in the numbers of boys or girls being born.

If your hospital won’t tell you, you may be able to pay privately to find out. Ask your sonographer or midwife for more information.