The 12 week dating scan is your first routine ultrasound on the NHS, usually performed between weeks 11 and 14. It confirms your due date, checks the baby's heartbeat and development, screens for chromosomal conditions through the combined test, and determines whether you are carrying multiples. The scan is free, takes 10 to 20 minutes, and is performed by a trained sonographer.
The 12 week scan, also called the dating scan or first trimester scan, is a routine ultrasound offered to all pregnant people on the NHS. It is usually carried out between 11 weeks and 13 weeks plus 6 days of pregnancy. This scan is a key part of your antenatal care and provides important information about your pregnancy.
The scan is performed by a trained sonographer using an abdominal ultrasound probe. A small amount of gel is applied to your tummy, and the probe is moved across your skin to produce real-time images of your baby on a screen.
Due date. The baby is measured from crown to rump (CRL measurement) to calculate your estimated due date. This is the most accurate way to date a pregnancy and may change the date calculated from your last menstrual period. According to NICE, ultrasound dating in the first trimester is accurate to within plus or minus 5 days.
Heartbeat. The sonographer will confirm that the baby''s heart is beating. By 12 weeks, the heart rate is typically between 120 and 180 beats per minute.
Development. The scan checks that your baby is developing normally. The sonographer will look at the head, brain, spine, limbs, abdominal wall, and stomach. By 12 weeks, all major organs have formed and the baby is around 5 to 6 centimetres long.
Multiples. The scan will reveal whether you are carrying one baby, twins, or more. If multiples are detected, the sonographer will determine the type of twin pregnancy.
Placenta position. The location of the placenta is noted. If it is positioned low, this will be monitored at your 20 week anomaly scan.
If you choose to have screening for chromosomal conditions, the combined test is usually performed at the same appointment. This is entirely optional and you will be asked for your consent.
Nuchal translucency (NT) measurement. The sonographer measures the fluid at the back of the baby''s neck. A larger than average NT measurement may indicate a higher chance of conditions such as Down''s syndrome (trisomy 21), Edwards'' syndrome (trisomy 18), or Patau''s syndrome (trisomy 13).
Blood test. A sample of your blood is taken to measure levels of free beta-hCG and PAPP-A. These hormone levels, combined with the NT measurement and your age, are used to calculate your individual risk.
Results are given as a probability. A result of 1 in 150 or higher is considered ''higher chance'' and you will be offered further diagnostic testing, such as NIPT, amniocentesis, or CVS. The combined test detects approximately 85% of pregnancies with Down''s syndrome, according to NHS Screening.
Drink water. You may be asked to arrive with a full bladder. Drinking around 500ml of water an hour before your appointment can help. Check your appointment letter for specific instructions.
Wear comfortable clothing. You will need to expose your tummy area, so a loose top that can be easily lifted is practical.
Bring your notes. Have your maternity notes or NHS number with you.
Your partner or support person. Most NHS trusts allow one person to accompany you. Check with your hospital in advance.
You will lie on a bed, slightly reclined, and the sonographer will apply warm ultrasound gel to your tummy. The probe is moved across your skin to capture images. The scan is painless, though the pressure of the probe and a full bladder can feel slightly uncomfortable.
In some cases, a transvaginal scan may be needed for a clearer view. You will always be asked for consent first. The whole appointment typically takes 10 to 20 minutes.
The sonographer will share the key findings during or immediately after the scan. Your estimated due date will be updated if it differs from the date based on your last period. If you had combined screening, blood test results usually take 1 to 2 weeks.
If anything unexpected is found, you may be referred to a specialist for further assessment. This does not automatically mean something is wrong.
Your next routine scan will be the 20 week anomaly scan.
The 12 week scan is generally too early to determine the baby''s sex with certainty. Most NHS trusts offer sex determination at the 20 week anomaly scan, though some trusts have a policy of not disclosing sex at all.
The appointment usually takes 10 to 20 minutes, though you may spend longer in the waiting room.
Often yes. Most NHS trusts recommend drinking around 500ml of water an hour before your appointment.
Yes, the dating scan is a routine part of NHS antenatal care and is completely free. Printed photos may carry a small charge.
The sonographer may ask you to move position, walk around, or return for another scan. A transvaginal scan may be offered.
No, the combined screening for chromosomal conditions is entirely optional.
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