Your 12 week scan: what happens, what they check, boy or girl guesses

The letter says 11:40 on a Tuesday, drink a pint of water an hour before, and you've been counting down to it since the second line on the test. Most people are more nervous about this one than the 20 week scan, because it's the first time anyone looks.

Here's what happens in that room, what the sonographer is checking while you stare at the screen, what the screening is for, whether your due date will move, and a straight answer on boy or girl. The picture can't tell you. We'll get to that.

• You may need a full bladder, the NHS says, because it makes the picture clearer. Ask your midwife before the day.
• Screening for Down's, Edwards' and Patau's syndromes is a blood test plus that neck measurement. It's your choice, and the results come within 2 weeks.
• Finding out the sex isn't part of NHS screening. Some hospitals will tell you at the 20 week scan, if your baby cooperates.

What happens at the 12 week scan

Your midwife or doctor books it, usually at your local hospital's ultrasound department, and the NHS 12 week scan page says most scans are done by a sonographer. You lie on your back in a dimly lit room with your tummy out, they put cold gel on it, and a probe goes over the skin. They may press a little to get a better view.

The screen is angled for the sonographer first, not you. They need the views, and for the first few minutes they're measuring, so don't panic at the silence.

The NHS says a scan usually takes around 20 to 30 minutes, and that if your baby is lying awkwardly or won't keep still it can take longer, or occasionally has to be repeated another day. You get the results there and then.

You can take someone with you. Most hospitals don't allow children at scans because there's no childcare, so ask before you bring a toddler. And check whether your hospital does pictures, because the NHS says there may be a charge, and nobody wants to find that out at the desk.

What the 12 week scan checks

Five things, and the sex isn't one of them.

That's the whole job. It's a measuring appointment, and the picture you take home is a side effect of it, which is worth remembering when the group chat starts reading the picture for clues.

The combined screening test, and whether to have it

Your midwife usually explains this at the booking appointment, and the NHS screening page is clear that it's offered to everyone and it's your choice. You can screen for all three conditions, for Down's syndrome only, for Edwards' and Patau's syndromes as a pair, or for none of them.

The combined test has two parts: a blood test from your arm at 10 to 14 weeks, and the neck fluid measured on the scan at 11 to 14 weeks. They're usually done on the same visit. The NHS says there are no known risks to you or your baby from either.

If your scan happens after 14 weeks, the combined test is off the table and you're offered the quad test instead, a blood test at 14 to 20 weeks that the NHS says isn't as accurate.

What the results look like

Within 2 weeks. A lower chance result comes by letter with a figure on it, something like 1 chance in 300, and the NHS says most people get this one and aren't offered any further tests.

A higher chance result comes by phone or in person within a week. The NHS puts it plainly: it doesn't mean your baby has the condition, and most people with a higher chance result go on to have a baby without any of the three.

You're offered an appointment to talk it through. From there you can choose a more accurate screening blood test called NIPT, a test that can tell you for certain (chorionic villus sampling or amniocentesis), or nothing more at all.

If you said no at booking and you've changed your mind, tell your midwife or GP. And if you're between 10 and 14 weeks and nobody has offered it, the NHS says to raise it yourself.

Antenatal Results and Choices run a helpline for anyone waiting on or holding a result: 020 7713 7486, Monday to Friday, 10am to 5.30pm.

Will your due date change?

Often, by a little. Your due date so far is counted from the first day of your last period, and the NHS says the scan gives a better idea of how many weeks you are, so the date may be adjusted to match the measurements. If it moves, the new one wins, for everything.

Put it into our due date calculator afterwards. It works from a scan date as well as a period date, and gives you the two numbers work will ask for later: your expected week of childbirth, and the earliest your maternity leave can start.

Boy or girl at the 12 week scan?

Not from the NHS. Finding out the sex isn't part of the screening programme, and the sonographer at the dating scan is measuring, not sexing. You may be able to ask at the 20 week scan, between 18 and 21 weeks, if your hospital's policy allows it. Tell them at the start. Even then the NHS says they can't be 100% certain, and some hospitals have a policy of not telling at all.

Which is why the 12 week photo gets so much attention. Two theories claim to read it.

Skull theory looks at the head: a boy is supposed to be big and blocky with a sloping forehead and a square chin, a girl rounder and tapering at the top. Nub theory looks lower down, at the angle of the little bump between the legs against the line of the spine, with 30 degrees as the line between boy and girl.

Both guides walk you through your own picture, and both say the same thing at the end: it's a bit of fun, a coin gets it right half the time too, and nobody can tell sex from a 12 week scan.

Keep the profile shot, though. It's the one both theories need.

How to get ready for it

Ask your midwife whether your hospital wants a full bladder, and if so drink before you leave the house, not in the car park. Bring your maternity notes.

Write your questions on your phone. You'll forget every one of them the moment the screen comes on.

If the appointment is in work time, gov.uk says you get paid time off for antenatal care at your normal rate, but only once your employer knows you're pregnant. A lot of people haven't told work by the 12 week scan, which means a day's holiday for this one. Your partner can take unpaid time off for two appointments.

If you'd rather nobody guessed before you're ready, the first trimester to do list has the telling people section, and when do you start showing explains why it's bloat, not bump, at this point.

What to wear to your 12 week scan

Two pieces. The gel goes on your lower tummy, so you want a top that lifts and bottoms that pull down a few inches without a fight. A dress means lying there in your pants with it bunched under your chin.

By 12 weeks a lot of people have hit the stage where the jeans do up but you'd rather they didn't. Soft leggings with a panel that comes up over the tummy pull down for the scan, go back up without digging in, and don't look like maternity wear to anyone in the waiting room.

One reviewer bought hers at exactly this point: "I'm only 13 weeks pregnant at the moment but my jeans have already started to be too tight. Not that they don't fit just at that uncomfortable stage." She went on: "even at my tiny bump state they fit like a glove and have room for the bump to grow".

If the scan finds something

The NHS says most scans show the baby developing normally, because most babies are healthy. If the sonographer sees something that makes a condition more likely, they may ask a colleague for a second opinion in the room, and you might be offered another test to find out for certain.

Nothing happens without you choosing it. The NHS says you'll be given more information about any further test so you can decide, with your midwife or a consultant, and you may be referred to a specialist, sometimes at another hospital. The NHS page on what happens if screening finds something is the one to read that evening, not the forums.

Questions we get asked

Do you need a full bladder for the 12 week scan?

You may. The NHS says a full bladder can make the ultrasound image clearer, and to ask your midwife or doctor before the scan whether your hospital wants one.

How long does the 12 week scan take?

The NHS says the dating scan usually takes about 20 minutes. It can run longer if your baby is lying in an awkward position or moving about, and occasionally the scan has to be repeated on another day to get a clear picture.

Can you find out the sex at the 12 week scan?

No. Finding out the sex isn't offered as part of the NHS screening programme at any scan. You may be able to at the 20 week scan, depending on your hospital's policy, and even then the sonographer can't be 100% certain.

What if my 12 week scan is after 14 weeks?

You still have the dating scan, but the NHS says you won't be offered the combined screening test. Instead you're offered the quad test, a blood test between 14 and 20 weeks that checks for Down's syndrome and isn't as accurate as the combined test. Edwards' and Patau's syndromes are also checked for at the 20 week scan if you choose to have it.

Can I bring my partner or my other children?

You can bring someone with you, and most people do. Most hospitals don't allow children at scans because there's no childcare, so check with yours before the day.

Is the 12 week scan safe?

The NHS says there are no known risks to you or your baby from an ultrasound scan, and that it's your choice whether to have it. If you decide not to, your antenatal care carries on as normal.

Scan date in the diary, notes in your bag, water in the car. Then enjoy the 20 minutes, because this is the first time you'll see them, and the picture goes straight on the fridge whatever anyone thinks it says.