What to expect from your 12-week pregnancy scan

The dating scan is usually done at some point between 8 weeks and 14 weeks pregnant. NICE recommends it's done between 10 weeks and 13 weeks. You will have had earlier appointments and may have had an early scan if you've had any concerns such as bleeding, but otherwise this is the first time you'll get to see your baby, so it's a real milestone in your pregnancy.

What happens during the dating scan?

Before the scan you will be asked to drink a lot of water and have a full bladder, as this puts the uterus in a better position to be scanned. This can be something of an uncomfortable challenge if your sonographer has particularly long waiting times.

I had to drink so much bloody water before my scan only to find there was a delay before my appointment – I felt like I was going to explode. I'll never forget one nurse asking me, 'Do you think you could just pop to the loo and let just a little bit out?' Errrr – NO!’

When it comes to the actual scan you'll lie on your back and then some sticky, clear gel will be rubbed over your abdomen. The sonographer will tuck some tissues under your clothes so you don't get gel all over them.

He or she will then move a hand-held transducer over your belly, which bounces high-frequency sound waves off your baby to create a picture on the monitor. You might feel a bit of pressure but it doesn't actually hurt and won't harm your baby. You should then see the black-and-white image of your baby appear on the screen.

The clarity of the picture depends on a number of things. For instance, if you have any abdominal scarring or are overweight the picture may not be as clear.

Occasionally, if they can't see what they need to, the sonographer may ask you to have a transvaginal scan, where a very thin probe is used to look at the baby from close to the cervix. This gives a much clearer picture.

You will be able to watch the monitor and see the first pictures of your baby, which is always an extraordinary moment, whether this is your first baby or your fifth.

It may not be immediately obvious which parts of your baby you're looking at, but the sonographer will be able to help you work it out. He or she may need to prod your belly a bit to “encourage” the baby into a suitable position.

After a long first trimester, when you might well have had worries, or even wondered if there can really be a baby in there, it is a great comfort and a huge relief to see your baby on the screen and have the reassurance that everything is OK in there.

What does the 12-week scan show?

The scan is primarily for dating but the sonographer will also look in on a few more things at the same time. Here are the main checks they'll be making:

Your baby will be measured and the exact stage of pregnancy will be calculated from the measurement made from crown to rump. This will give you a more precise estimated due date.

The number of babies

Are you expecting just one baby, or could it be twins or (gulp) even more?

Development and growth

The sonographer will check your baby's spine for any visible abnormalities. They will also look at the head, limbs, feet, heartbeat and check that the major organs are developing as they should.

The health of the placenta

They will look at the placenta itself and will take note of its position, which may have implications for later in the pregnancy. A low-lying placenta usually moves up later in the pregnancy but if it doesn't, it can cause problems in labour so they will want to check its movements throughout your pregnancy.

How accurate is the dating scan?

It's not completely foolproof – but the dating scan is a much more accurate way to work out how far you are into pregnancy than calculating it by the date of your last period, which is the only method the midwives will have used so far to work out your due date.

You may find at this scan your due date is altered on your notes. It's more common to be told you're less far along than you thought you were, rather than that you're actually further along in the pregnancy.

Will they do screening tests at the same as my dating scan?

You may also be offered a nuchal translucency test at this appointment. This is a measurement of the amount of fluid at the base of the baby's neck and it can indicate a higher risk of Down's syndrome. Not all areas offer this test as routine but when it is offered it is usually done at the 12-week scan.

The results of the nuchal test are put together with the results of blood tests that are usually done a bit earlier to screen for the risk of your baby having conditions such as Down's, Edwards and Patau syndrome.

The “risk” will be expressed as a number, for example, one in 450. If you're pregnant and over 40 it's worth bearing in mind that your risk factor will automatically be higher because of your age.

The pregnancy screening tests and scans you'll be offered vary slightly between different parts of the UK, so ask your midwife or GP what's available at the hospitals in your area.

What happens if the scan finds a problem?

If a problem is picked up on the dating scan you will usually be offered further tests and referred on to a more specialist department to find out more about what's going on.

If the screening tests find that your risk for any of the abnormalities tested for is high, you will be offered diagnostic tests such as CVS (chorionic villus sampling) and amniocentesis to find out for sure if there's a problem. You're under no obligation to have these, and they do usually carry a small risk of miscarriage as they are invasive.

Are there any risks connected with the 12-week scan?

These pregnancy scans pose no risk at all to either you or your baby. However, you may want to think in advance about whether you want the screening test, as it could always throw up something that then means another difficult decision such as whether to have diagnostic tests. If you know you wouldn't go down that route it's worth considering whether to have the screening in the first place.

While the vast majority of women take up all the scans they are offered, and they can offer really important information about your baby, you are not obliged to have any of them at all if you don't wish to.

Can I bring my partner or a friend to the scan?

Hospitals are usually happy for you to bring your partner or someone else to the scans. Check your hospital's policy, as some don't allow more than one person in the room with you, or don't allow children to come.

It's nice for you to have a bit of moral support but it is also a really special moment for your partner, who may have found they feel at a slight “remove” from the pregnancy so far, not being quite so “at the coalface” of things as you are.

How long does the 12-week scan take?

The scan takes around 20 minutes but the whole appointment itself might take a little longer.

Can the 12-week scan tell me if I'm having a boy or a girl?

It's probably too early to tell at this stage. Some sonographers would be able to take an educated guess but they won't usually tell you as they could easily be wrong. You should be able to find out your baby's sex at the anomaly scan at 20 weeks, but check with your hospital as some have a policy of not telling parents the sex at all.

Will I get a picture of my baby at the 12-week scan?

Most hospitals will give you a picture of your baby to take home. Some even do DVDs. You may have to pay for either or both of these so check beforehand and take along some cash on the day if you want to keep a copy of your baby's first snapshot.

How big will my baby be at my dating scan?

That depends on exactly when you have the scan done, because your baby is growing fast at this stage. At 10 weeks gestation she's around 3cm long, but by 13 weeks she's around 7cm.