12 Week Scan: What to Expect, Week by Week

The 12 week scan is, for many parents, the first proper look at their baby, and it does a lot of quiet work behind that exciting screen image. Also called the dating scan, it confirms how far along you are, checks how many babies there are, and can form part of early screening. This guide walks through what the scan checks, when it happens, how to prepare, and why the person to explain your results is always your own midwife or doctor.

What the 12 week scan is

The 12 week scan is an ultrasound examination, meaning it uses high-frequency sound waves and a handheld probe to build a live image of your baby on a screen. Its main job is dating: measuring your baby to estimate how many weeks pregnant you are and to calculate a due date, which is often more accurate than dates based on your last period. According to the NHS guide to the 12 week scan, this dating scan is usually offered at around 10 to 14 weeks and takes about 20 minutes. If you would like a deeper look at the measurements involved, our companion piece on the 12 week ultrasound and what results mean goes further into the detail.

When the scan happens, week by week

Timing matters, because the scan works best within a particular window.

• Before about 10 weeks: the baby is very small, so dating is usually done a little later unless there is a specific reason to scan early.
• 10 to 14 weeks: the usual window for the dating scan, when measurements are reliable for estimating your due date.
• 11 to 14 weeks: the window in which combined screening, including the nuchal translucency measurement, can be offered if you choose it.
• After 14 weeks: if dating was not done earlier, your team will use other measurements, and screening options change.

These are general patterns. Your own schedule depends on your care provider and when your pregnancy is confirmed, so follow the appointments your maternity team arranges.

What the scan checks

Although parents often think of it simply as the first photo, the dating scan is doing several practical checks at once. The NHS notes that it estimates gestational age and the due date, confirms whether you are carrying one baby or more, checks that the pregnancy is developing in the right place, and looks at early development, including some conditions such as spina bifida. It is a reassuring milestone, but it is a check, not a guarantee, and any findings are followed up by your clinical team rather than settled on the day.

Screening and the nuchal translucency

Between about 11 and 14 weeks, the dating scan can also be part of combined screening for Down's syndrome and, in some programmes, Edwards' and Patau's syndromes. This uses a measurement of the fluid at the back of your baby's neck, called the nuchal translucency, together with a blood test, to estimate a chance, not a diagnosis. Screening is your choice, and you can accept or decline it. If you want to understand this part in more depth before your appointment, our guide to the nuchal scan week by week explains how the measurement is taken and what a screening result does and does not mean.

How to prepare

Preparation for a dating scan is simple, but a couple of steps help the sonographer get a clear picture:

• Arrive with a full bladder: the NHS notes you may be asked to have a full bladder for this scan, as it makes the ultrasound image clearer. Follow the instructions in your appointment letter.
• Wear a two-piece outfit: only your lower tummy needs to be exposed, so separates are more comfortable than a dress.
• Bring your notes and any questions: it is easy to forget things in the moment, so a short list helps.
• Consider who comes with you: policies on guests vary, so check with the department beforehand.

What happens during the scan

The scan itself is straightforward and painless. You lie back, the sonographer applies a little gel to your tummy, and moves a probe across the skin to bring your baby into view on the screen. Most dating scans are done this way, across the abdomen. Occasionally, if the view is unclear or it is very early, a transvaginal scan gives a better image; our overview of how a transvaginal ultrasound works explains what that involves. The sonographer concentrates on measurements during the scan, so there may be quiet stretches while they work, which is completely normal.

Is the 12 week scan safe?

Ultrasound is considered very safe. The NHS guide to ultrasound scans states that the sound waves used in ultrasound scans are safe and that scans do not use any radiation, unlike X-rays or CT scans. RadiologyInfo.org adds that ultrasound has been used to evaluate pregnancy for nearly four decades with no evidence of harm to the patient, embryo or fetus. That safety is one reason ultrasound is the workhorse of pregnancy care. For the bigger picture of appointments ahead, our overview of scans during pregnancy and the general pregnancy sonogram guide map out what comes next, including the detailed anatomy scan later on.

Frequently asked questions

When is the 12 week scan done?

The dating scan is usually offered at around 10 to 14 weeks of pregnancy and typically takes about 20 minutes. If combined screening is part of your care, the relevant measurement is taken between about 11 and 14 weeks. Your exact appointment depends on your maternity team and when your pregnancy is confirmed.

What does the 12 week scan check?

It estimates how many weeks pregnant you are and calculates your due date, confirms whether you are expecting one baby or more, checks that the pregnancy is in the right place, and looks at early development, including some conditions such as spina bifida. It is a check rather than a guarantee, and findings are followed up by your clinical team.

Do I need a full bladder for the dating scan?

Often yes. The NHS notes you may be asked to have a full bladder for this scan, because it makes the ultrasound image clearer. Always follow the specific instructions in your appointment letter, as guidance can vary between departments.

Is the 12 week scan safe for my baby?

Yes. Ultrasound uses sound waves, not radiation, and the NHS states the sound waves used in scans are safe. Obstetric ultrasound has been used for decades with no evidence of harm to the patient, embryo or fetus. If you have any concern, your midwife or doctor can talk it through with you.

Can the 12 week scan tell me my baby's sex?

The dating scan is focused on measurements and early checks, not sex determination, and it is generally too early to tell reliably. Sex is more commonly discussed at the later anatomy scan, and even then it is not the purpose of the exam. Ask your maternity team about their policy.